International RILEM Conference on Synergising Expertise towards Sustainability and Robustness of Cement-based Materials and Concrete Structures

Pozzolans were used selectively in combination with lime to produce mortars used in structures where watertightness was required such as aqueducts, baths and pipes many centuries ago. The appreciated properties of mortars containing pozzolans were the increased durability and strength and the dense structure in relation to pure lime mortars. Ancient engineers managed to produce composites which proved their durability and their study provides significant information to modern materials technology. Today, natural pozzolans are used as binders for the production of mortars in order to produce repair materials compatible to old authentic mortars and also in cement industry. Thus, the reserves of natural pozzolans are not sufficient for the explosive development of the construction sector. Additional sources of pozzolanic materials were sought, such as industrial by-products used as supplementary materials. In the case of their use, the purpose is not only the safe and massive disposal of large quantities of materials that would otherwise burden the environment, but also the utilization of their special characteristics to produce different types of composites. Recent studies have documented that waste perlite, may present induced pozzolanic reactivity and could be used as an alternative pozzolanic material. Additionally, the substitution of natural pozzolan with waste perlite in lime-based mortars and grouts, has proved to be beneficial for their overall performance.

Several slag-blended cement hydration models widely used in the cement research field are benchmarked in this work, with a focus on their hypothesis, assets and drawbacks. The effect of slag on the hydrating mixture and the hydration products composition and quantities is considered. Different cement hydration models are presented in this study: analytical models such as Chen & Brouwers’ and Kolani's models and generic numerical hydration models as CEMGEMS and VCCTL. Powers’ and Tennis & Jennings’ models are also used for comparison for compositions without slag-substitution. Computed results obtained with these models such as the degree of hydration and the hydration products composition and quantities are compared with experimental results found in the literature.

High-level replacement of clinker by supplementary cementitious materials (SCMs) offers a well-tried solution to reducing CO2 emissions of cement production. To sustain further clinker reductions, new sources and combinations of SCMs will need to step in and their impact on cement hydration will need to be understood as, for instance, in comprehensive hydration models. A key input for cement hydration models, whether based on thermodynamic, microstructural, or simple mass balance principles, are time-dependent data on reaction degrees of all cement constituents. These kinetic data are usually introduced either directly from experiments or from empirical models fitted to experimental data. While reliable reaction degree data are relatively straightforward to obtain for the well-known, crystalline clinker phases in cement, advanced analysis techniques are required to estimate reaction kinetics of amorphous phases, present in most SCMs. Generic kinetic models for SCM reaction are therefore of interest to explore and predict the impact of SCM reactions on the cement hydrate assemblage, and eventually, performance.This contribution proposes a new approach to refine kinetic models for SCM reaction by derivation of model parameters from reactivity screening tests, such as the R3 test, reported in the published literature and case studies. It is discussed how this approach can be used to model reactivity of SCMs and how it can be used and extended to investigate and parameterize kinetic interactions in hydration of SCMs.

The major concern of the modern cement industry is to minimize the CO2 footprint. Thus cement based on belite, an impure clinker mineral (CaO)2SiO2 (C2S in cement chemistry notation), which forms at lower temperatures, is a promising solution to develop eco-efficient and sustainable cement-based materials, used in enormous quantities. However, the slow reactivity of belite limits its application. To understand the reasons behind, dissolution mechanisms and kinetic rates at the atomistic scale provide fundamental insights. This work aims to understand the dissolution behaviour of different surfaces of β-C2S providing missing input data and an upscaling modeling approach to connect the atomistic scale to sub-micro scale. First, a combined ReaxFF and metadynamics-based molecular dynamic approach are applied to compute the atomistic forward reaction rates (RD) of calcium (Ca) and silicate species of (100) surface of β-C2S considering the influence of crystal surfaces and crystal defects. To minimize the enormous number of atomistic events possibilities, a generalized approach is proposed, based on the systematic removal of the nearest neighbour's crystal sites. This enables tabulation of data on the forward reaction rates of the most important atomistic scenarios, needed as input parameters to implement the Kinetic Monte Carlo (KMC) computational upscaling approach, presented in Part-2 paper of this proceedings.

Water transport is critical for the durability and confinement performance of cement-based materials. C-S-H, the primary phase in hydrated cement-based materials, is nanoporous, contributing therefore to water transport. To understand water transport in C-S-H, it is necessary to deploy well-suited techniques and theoretical framework to deal with the nanoscale. Einstein linked the dynamics of a diffusing particulate system described by the mean-squared displacement (MSD) to the (self)-diffusion. The self-diffusion is, in turn, related to viscosity via the Stoke-Einstein relation. Using (equilibrium) molecular simulations, the self-diffusion of water in C-S-H is computed via the Einstein MSD equation. Using non-equilibrium molecular simulations of pressure-gradient-driven flows in C-S-H, it is shown that the Stokes-Einstein equation captures viscosity changes with the pore size expected in nanoporous materials. These results suggest that a fundamental link between diffusion and permeability can be established for C-S-H. Further, mean-field homogenization is deployed to get the effective diffusion and permeability of C-S-H at the gel scale. The results obtained are in good agreement with the available experimental data. In particular, it is finally possible to explain why the water permeability of the C-S-H gel (7 × 10−23 m2), as early calculated by Powers based on experiments, is so low. The strategy deployed here can be extended in future work to understand ion transport and unsaturated transport in C-S-H.

Upon heating, thermal pressurization of the fluid in a porous media may occur according to the poromechanical boundary conditions. This pressure build-up may exceed material strength leading to explosive spalling. Thermal pressurization is a mechanism evoked to explain fire spalling of concrete and is also relevant to applications such as well cement lining in petroleum engineering and nuclear waste disposal structures in which the material is subject to significant temperature changes. The contribution of water in C-S-H gel and interlayer pores to thermal pressurization is yet poorly understood. In this work, we study the evolution of the pressure in C-S-H for different pore sizes (micro-and mesopores) as a function of temperature in undrained and drained conditions using molecular simulations. For the drained case, we consider two different poro-mechanical conditions, the first one at 100% relative humidity (liquid saturated system), and the second one at a constant vapor pressure equal to 0.1 MPa. By analyzing the confining pressure, we show how confinement affects the pressure buildup in the three different poromechanical conditions. We also study water desorption in C-S-H interlayer pores and how confinement affects the liquid-gas water phase transition. We finally compare our model with other available data in the literature. Our collected data shows the importance of nanoscale processes to predict and understand thermal pressurization in cement-based materials.

The interpretation of dielectric measurements in cement-based materials, as well as multiscale modeling strategies, requires the knowledge of the intrinsic permittivity of their various constituent phases. Calcium silicate hydrates (C-S-H) is the major hydrated phase in concrete (when clinker is the main cement compound), but to date, its frequency-dependent complex dielectric response remains unknown. Direct experimental measurements of C-S-H intrinsic dielectric behavior are challenging due to the scales to be probed and the difficulties in isolating this component in cement systems. Molecular simulations arise as a helpful tool to provide reliable estimates of properties bottom-up. This study adopts a multiscale approach to estimate the complex dielectric response of C-S-H over a frequency range of [0; 100 GHz]. We perform molecular dynamics simulations to compute the frequency-dependent dielectric response of water in C-S-H using theoretical framework of Statistical Physics, which enables us to associate the microscopic decay in water polarization correlations to the dielectric response. Several configurations are considered by varying the interlayer distance, covering the range of pore sizes associated with interlayer pores and gel pores in C-S-H. The dielectric response is anisotropic and pore size dependent, as expected in layered materials. The results at the molecular scale are then used as inputs in a homogenization model to estimate the dielectric permittivity of C-S-H gel, which we compare with estimations obtained from inverse analysis based on Micromechanics. Our results are a valuable input for multiscale modeling of non-destructive testing and evaluation in cement-based materials.

Hydrogen embrittlement is one of the main causes of catastrophic failure of structural components made of carbon steel. Among the underlying physical mechanisms associated with this complex phenomenon, hydrogen diffusion as an atomic interstitial in the body - centered cubic (BCC) lattice of pure iron plays a fundamental role. The main goal of this study is to characterize the fundamental events that controls the diffusion of hydrogen: the atomic jumps among stable or metastable lattice points (tetrahedral and octahedral sites). To this end, the best technique available is density functional theory (DFT), which is able to determine from first principles the atomic configuration and the energy landscape associated to the presence of hydrogen in the lattice. In this work, the strategies employed so far to obtain the jump parameters are reviewed, and a recently developed technique (Linear synchronous transient and Quadratic synchronous transient method) has been applied in order to improve the accuracy of previous results.

Concrete structures can go through cycles of drying and saturation during their lifetime. In special cases, such as tunnels, dams, and piles, this phenomenon may occur frequently. Drying and saturation cycles should be considered because they adversely affect the short-term and long-term behavior of the structure. In this paper, a water transfer model is proposed to predict the moisture migration and water content field within the studied porous material. The switching between saturated and unsaturated states is done continuously, without resorting to a classical three state variables model, but using liquid pressure as a single state variable in the governing water transport equation. First, the hydric transfer model is presented. The underground structure subjected to drying and resaturation is then simulated in order to demonstrate the capacity and performance of the hydric model to consider simultaneously negative and positive liquid water pressure, which was not previously the case, for instance, in the classical Richards formulation. This example demonstrates the potential of the model to describe water transfer by smoothly transitioning from a drying condition to a saturated condition.

On Feb. 4th, 2022, a 9-m-high pre-fabricated concrete segment of the Israeli separation wall collapsed near the town of El Ram, north of Jerusalem. The failure occurred due to excavated soil wrongfully deposited against the back of the wall. The wall segments were not designed to carry lateral earth loading. As a result, they collapsed due to flexural failure. We back-analysed the failure event based on technical data and observations to obtain the wall loading. This analysis suggests that the internal moment at the time of failure was considerably greater than the capacity of the wall according to accepted standards. We then conduct numerical analysis using the Lattice Discrete Particle Model (LDPM), capable of capturing fracturing processes and complex failure mechanisms to replicate the actual collapse mechanism. This analysis accounts for the post-peak behaviour of the reinforced concrete up to the point of the wall's collapse. Identifying the failure in advance was crucial and prevented catastrophic outcomes by allowing time to react. However, the reinforced concrete residual state is far from being fully understood. While engineers cannot rely on structural elements’ residual state during design, a better understanding of this state is crucial for proper response and mitigation measures following the onset of failure.

The need for rehabilitation of existing structures is currently increasing and will continue to do so in the future. Reinforced concrete facings are considered an effective rehabilitation measure for damaged surfaces of massive concrete structures. The installation of the reinforcement for concrete facings, necessary for crack width control in the structure, is however time-consuming and expensive. The required reinforcement depends mainly on the development of the hydration heat and the resulting restrained deformations at an early age. This contribution presents a numerical model of the concrete facing and the existing structure for the simulation of the stress development due to the hardening of the concrete and the resulting crack formation. The results of the simulation should provide the basis for a future reinforcement optimization. For this purpose, the effect of different cements as well as the influence of the interaction with the existing structure are examined in this contribution.

The CO2 emissions due to the production of cement is a partly reversible phenomenon known as carbonation. The CO2 uptake occurs at each step of the life cycle of a structure, from the cradle to the grave as soon as concrete surfaces are in contact with atmospheric CO2. After concrete crushing, this carbon sink is amplified by the increase of material surface. However, the study of the carbonation of recycled aggregates is difficult to carry out in the laboratory or in situ. Physico-chemical modelling is therefore a powerful tool which should make it easier to explore the CO2 uptake. We propose here results from numerical simulations of carbonation at both the grain and the stockpile scales obtained during the French Project “Fastcarb”. Our purpose is to evaluate the efficiency of a process on recycled aggregates, and the influence of parameters assumed to control the CO2 uptake rate, such as ambient CO2 concentration, grain size and water content. Experimental data, gas diffusion tests and CO2 binding capacity and rate tests, give order of magnitude of time and length scales of interest through dimensionless numbers and are input to the full numerical model. The used model is formulated in terms of mass conservation equations for both water and CO2. Both dimensionless numbers and numerical results confirm that an accelerated process using industrial gases with high concentration (pCO2~20%) should be preferred to an atmospheric carbonation (pCO2~0.04%) to take full advantage of the CO2 uptake by recycled aggregates on short time scale.

As the owner of an extensive fleet of power plants, EDF is committed to the safe and sustainable long-term operation of massive civil engineering facilities. This involves inspection and auscultation of the current state of the structure, and structural computations to anticipate durability and to test mitigation strategies. Both require relevant material properties for the concretes at stake, which often cannot be measured directly, for either practical or economical reasons. The design of next-generation plants involves concrete mixes not yet existing, but whose behavior is required by structural engineers, to ensure that each facility correctly fulfills its function.Investigating the properties and behavior of cement based materials is thus of paramount importance. In addition to classical lab experiments, EDF is currently developing a “virtual lab” dedicated to concretes. It is based on a multidisciplinary platform, built taking advantage of recent advances in cement based materials modeling. A multiscale and multiphysics approach is adopted: materials are morphologically described down to the scale where the physical processes can be uncoupled, and where elementary constituents whose properties are mix independent can be identified. Then, upscaling techniques are used to estimate properties and behaviors at the engineering scale.The platform, named Vi(CA)2T, includes toolboxes to upscale mechanical behavior (stiffness, creep) and transport properties (dielectric permittivity). It adheres to an open design: new physics are straightforward to add. After discussing the platform design and the challenges raised by such an approach, examples of applications at EDF are presented.

Hardened cement paste is susceptible to frost damage. The use of an air entrainment agent makes concrete frost durable. This is explained by the presence of the protected paste volume in the vicinity of entrained air voids. In this study, a model using Dirichlet tessellation is proposed to estimate the protected paste volume associated with a random system of real air voids. The characteristic distance for the protection is defined by the ratio of the cumulative polygon tile areas to the entire cement paste. A critical distance is statistically determined by simulating random point patterns. To protect 95% of the paste area, the proposed model suggested that the average distance of about 0.22 mm should be protected at the maximum in a local region where air voids were sparsely present due to random fluctuation. This estimation was almost equivalent to the spacing factor recommended for the moderate exposure condition. This fact explains why the spacing factor has been useful as a safe characteristic distance parameter in determining air contents. The distance equivalent to the spacing factor reflects the most disadvantageous condition that can occur locally in the actual distribution of air voids against frost attack.

The long-term performance of new cementitious materials is uncertain. To help predict durability and manage uncertainty, the models must capture the fundamental mechanisms driving degradation in new binders. Such mechanisms evolve slowly and are strongly chemo-mechanically coupled, all of which challenges the existing simulations. This article presents MASKE: a simulator of microstructural evolution based on interacting particles, which represent multi-phase solid domains in an implicit ionic solution. Chemical reactions, sampled through Kinetic Monte Carlo to reach long time scales, determine precipitation/dissolution processes whose rates depend on solution chemical potentials and on particle interaction energy. Published results from MASKE have already addressed aggregation-driven precipitation of C-S-H nanoparticles, stress-driven dissolution of C3S crystals at screw dislocations, and carbonation of calcium hydroxide in a C-S-H matrix. Here new results are presented, focussing on a nanocrystal of calcium hydroxide and discussing: (i) its chemical equilibrium and dissolution/growth kinetics in stress-free conditions, and (ii) the emergence of pressure-solution and crystallization pressure when the crystal is compressed between platens. Similar chemo-mechanical processes contribute to important degradation modes of concrete, such as creep, sulphate attack, and alkali-silica reaction.

The elastic compliance of cementitious materials increases slightly, and their time-dependent “creep” compliance increases significantly with increasing temperature. The present contribution provides quantitative insight into this topic. Thereby, the focus rests on mature cement paste made from Ordinary Portland cement and distilled water. Macroscopic creep experiments were performed, in order to quantify both elastic and creep moduli in the range of temperatures from 20 ℃ to 45 ℃. The experimental results regarding temperature-dependent values of the modulus of elasticity are validated herein using original results from ultrasonics testing. Finally, a multiscale model was used to establish a link to well-known stiffness constants of unhydrated cement clinker, as well as to temperature-dependent elastic and creep stiffness properties of nanoscopic hydrate-gel needles.

Multiscale modeling is a powerful tool to understand and predict the overall mechanical and durability performance of concrete. However, considering properties at the microscale is challenging because of the highly heterogenous character of the cement paste microstructure, which includes porosity and several intermixed phases. The current work suggests a new experimental-modeling approach to model the 3D microstructure of cement paste, destined to multiscale modeling applications. Quantitative phase assemblage from X-ray diffraction (QXRD) conduced at different hydration ages combined with Gibbs Energy Minimization (GEMS) thermodynamic modeling serve to define microstructure phases to be modeled by µic model. Phase map from Electron Dispersive Energy Spectroscopy (EDS) mapping clustering is used to distribute microstructure phases into particles, hydrate layers or porosity. The µic microstructure model is then calibrated following an iterative process and using quantitative phase assemblages from thermodynamic modeling and QXRD analyses. The approach is applied to an Ordinary Portland Cement (OPC) system, for which the µic model is validated at the long-term hydration age. The results show that the calibrated µic model agrees with thermodynamics modeling results. This allows a more realistic representation of the cement paste microstructure. Therefore, a more accurate prediction of the mechanical behavior of concrete when the model is used as input for multiscale modeling of concrete.

Long-term abrasion has been a significant durability problem for hydraulic concrete structures. This work proposes combined experimental and numerical approaches in investigating concrete abrasion behaviors. A laboratory setup has been built to simulate the abrasion process of concrete subject to sediment particles transported by water similar to natural conditions. Three-dimensional (3D) scanning analyses of the abraded concrete samples are then conducted to investigate the abrasion surface morphology and quantify the abrasion depth. Based on the obtained experimental results, numerical calculation studies are performed, aiming to develop a model that can account for important mesoscale factors for concrete abrasion and predict the abrasion damage behaviors of concrete structures. Mesoscale concrete is modeled as a heterogeneous 3-phase material composed of coarse aggregate particles, cement mortar matrix, and interfacial transitional zones (ITZs). Numerical calculations based on the generated mesoscale model are carried out to further study the effects of the interfacial bond and aggregate distribution on the abrasion resistance of concrete. The preliminary results show that mesoscale properties of concrete are very relevant in understanding the abrasion mechanisms and behaviors.

Concrete durability plays an important role in the serviceability of reinforced concrete structures. Deformation induced by shrinkage and thermal strains can lead to the initiation of cracks which in turn may develop into structural damage during several decades of service life. It is time-consuming and impractical to experimentally investigate the long-term mechanical behavior considering environmental influence factors. Hence, a state-of-the-art numerical simulation framework combining the Lattice Discrete Particle Modelling (LDPM) with a multi-physics framework is applied, coupling the mechanical behavior and chemical mechanisms of concrete at an early age and beyond. Based on an equivalent rheological model, the overall age-dependent deformations of concrete can be split into contributions from different physical phenomena assuming the additivity of strain and strain rate in the sense of one-way coupling. The hygro-thermal-chemical model describing the moisture transport, heat transfer and curing reaction drives the development of mechanical properties due to ongoing curing but also thermal and hygral eigenstrains. LDPM reflects the inherently heterogeneous nature of the material concrete at the mesoscale consisting of aggregates and mortar. The effect of aggregate volume and stiffness on concrete shrinkage is investigated by a newly proposed formulation for drying shrinkage of concrete. The results give robust predictions of macroscopic shrinkage for concretes with different mix proportions. A well-established experimental test campaign is selected to calibrate and validate the numerical model, which shows a good agreement and offers promising new insights into the cracking behavior of heterogeneous materials with acceptable computational cost.

Conventional structural design in building construction is commonly based on the static analysis of the load flow using 2D submodels. Hence, the deformation compatibility and stress redistribution between the structural members of the building are not adequately regarded. In addition, the structural and the subsoil responses are usually assessed based on isolated analyses which use the subgrade reaction modulus as a coupling interface. Many researchers have shown that using the subgrade reaction method can lead to an uneconomic foundation design. Furthermore, the subsoil response generally affects the submodel of the foundation slab or basement, respectively. This leads to a strong simplification of the total stiffness of the building, and results either in conservative or unsafe results depending on the members under consideration. In contrast, the static analysis with a holistic 3D model allows for a more realistic load flow within the building. However, this requires not only an accurate representation of the stiffnesses of the structural members and their connections in the respective limit states, but also an accurate representation of the ground deformation in the calculation model. This contribution aims to enhance the interoperability between geotechnical and structural engineering for 3D building models. The contribution begins with a critical assessment of the subgrade reaction method. The core of this contribution proposes an alternative approach to account for soil-structure-interaction effects for 3D building models by exchanging nodal displacements, instead of using the subgrade reaction modulus.

The construction industry faces the challenge of building sustainable and ever faster. The modular construction method with serial precast concrete modules is suitable to achieve this. Here, entire load-bearing structures are segmented into identical or similar modules, which are prefabricated and merely assembled on the construction site. However, the production of precast concrete components has so far by no means been an automated process, as there are hardly any repetition rates. Therefore, Industry 4.0 (I4.0) methods are to be transferred to the prefabrication process, targeted here in line with serial production. The aim is to mass-produce precast concrete modules with high precision and quality assurance in modern production systems based on the I4.0 concept. I4.0 refers to automation through continuous digitalization and networking of production. In the sense of I4.0, smart products seek an optimal path through production systems that interact with machines and processes self-controlled and self-managed. Thereby, the digital twin as a virtual representation for capturing and providing all relevant data is a key component. As a first step towards a holistic digital representation, a high-performance precast concrete module is presented in this work as both a digital twin and a real demonstrator. This Y-shaped module is part of a wall-like honeycomb structure. It is produced using rapid heat treatment and monitored by geometrical and thermal sensors during production and afterwards. The Asset Administration Shell (AAS) as the technical implementation of the digital twin in I4.0 is used to provide suitable methods for communication and interaction.

The focus of the contribution is the integral design of buildings by means of interdisciplinary cooperation between architecture and structural engineering. This interdisciplinary cooperation is enabled through a BIM-based platform, where all technical departments, beginning from architecture and structural design but also house technic and electrical engineering participate in the process and work as a single central work team. In particular, the opportunities of a BIM-based planning for an early planning stage involvement of structural engineers in the practice are analysed. The aim is hereby a better load flow representation and more precise regard of soil structure interaction in early planning stages by using a preliminary 3D analysis model derived from the existing BIM model at that time. In addition, the contribution discusses the opportunity of a quality increase of the BIM model itself due to involvement of structural engineers at the early planning stages, which results in neater and simpler planning and construction stages. Based on an actual project, some examples are presented to illustrate how early coordinated structural planning minimizes considerably the effort in further construction stages, for instance, the elaboration of formwork and reinforcement plans as well as position plans, reducing in consequence the risk of making typical mistakes during the design. Finally, the possibility of applying new sustainable concepts in the early stages of the project is presented as an advantage for the structural optimization and reduction of construction costs.

Technology, innovation, and data-driven business models are now transforming many areas of human activity to meet the challenges of a sustainable future, and the AEC sector is no exception since its material processes cause enormous resource depletion and waste generation. Even though a major part of construction and demolition waste is composed of materials with re-use/recycling potential (e.g., brick and concrete) which could contribute towards a circular economy, the industry’s performance in circularity is considered insufficient. According to the EU, the circular economy agenda should be in line with the digital agenda. Yet, the former is considered unachievable without advancement in digital technologies, which remain poorly deployed in the sector. Bearing this in mind, this paper reveals the approach of the RecycleBIM project, which intends to make an effort towards the creation of an integrated framework for the circularity of raw materials in construction with the use of progressive methodologies, such as Building Information Modelling (BIM) and information management. The article provides a description of the project’s proposed workflow and developments that enable intelligent applications of digital technologies in deconstruction activities. The paper includes the prerequisites to the use of BIM as well as descriptions of the key enablers of the proposed approach: the established information requirements, the data collection and processing techniques, open data formats, and open-source development with web-services integration. The case study with the validation of the proposed workflow is briefly described, and prospective opportunities are outlined in the closing sections.

The Architecture, Engineering, Construction, and Operation (AECO) industry is shifting toward the digitalization of its processes, with Building Information Modelling (BIM) methodologies. The use of BIM in AECO industry requires the definition of data requirements for the information exchanges between stakeholders. Data definition and management present a relevant challenge for implementers and can be hindering the spread of BIM in the industry. Product Data Templates (PDTs) are essential contributions to solving this matter through standardization and digitalization of construction product data. However, there seems to be a slow uptake of initiatives that provide open PDTs for the industry to adhere to the latest PDT standards, like EN ISO 23386 and EN ISO 23387. The lack of open PDTs for concrete-based materials/products is an illustrative example of the limitation reported. In such concern, and to contribute to the discussion of PDTs in the concrete industry, this paper proposes a PDT for pre-cast concrete beams. The PDT considers several sources of information such as Construction Product Regulations (CPR), Environmental Product Declarations (EPD), Industry Foundation Classes (IFC), and in-situ and laboratory tests, among others. This PDT will help push towards the digitalization and standardisation of data for concrete elements in BIM models and facilitate their use in BIM processes, including sustainability analyses.

Assessing fluid leakage rates through cracks in concrete structures is essential in many fields (nuclear safety, fluid storage, durability of structures). In previous works, the authors proposed experimental setups and procedures to study water and air leakage through cracked concrete specimens under Brazilian loading conditions. In the present contribution, the previous setup for air leakage is adapted to measure fluid pressure inside a so-called “realistic” crack representative of an actual crack surface geometry. The specimen is made by precisely casting a concrete crack surface. The procedure allows to realize it in two blocks (upper and lower) separable along this reproduced surface. The lower block is drilled with four thin cylindrical holes opening into the crack and which, once the specimen is installed on the press, are connected to pressure sensors. The specimen is inserted into an airflow circuit, and particular attention is paid to avoiding parasite leaks. Different inlet/outlet pressure conditions combined with different crack openings are imposed. Two different crack surface geometries are tested: plane and realistic. The results show non-linear air pressure distributions inside the realistic crack and non-negligible head losses at the inlet and outlet sections of the flow. Consequently, additional non-linear effects appear in the relationship between mass flow rate and squared pressure gradient due to the geometry of the realistic crack. These results demonstrate that measuring only the pressures in the upstream and downstream reservoirs, as classically done in standard protocols from the literature, can lead to a misinterpretation of the experimental results.

Owing to their high surface-to-volume ratio, concrete pavements and slabs are more prone to shrinkage, leading to premature cracking and, as a result, loss of serviceability. Capillary pressure in concrete, identified as the main contributor to shrinkage, needs to be frequently monitored to evaluate the shrinkage behaviour of concrete. However, capillary pressure measurement is currently limited to 100 kPa, covering only the initial few hours of age due to the low capacity of existing capillary pressure sensors. This results in very limited record of capillary pressure during the processes occurring within concrete after casting and has prevented a better understanding of the influence of capillary pressure on concrete durability. In this study, high capacity tensiometers (HCTs) were used for the first time to investigate the evolution of capillary pressure in early age concrete over longer periods and at higher capillary pressure values. The results showed that HCTs can quantify the evolution of capillary pressure up to 2000 kPa, a twenty fold increase in comparison to existing methods. This new transformative technology is a major step forward in concrete research and can provide new insights into the shrinkage behaviour of early age concrete. Furthermore, this novel technique can be used in situ in construction projects to monitor the real-time development of capillary pressure of concrete at an early age, aiding practitioners in the decision-making for the employment of effective mitigation strategies to reduce shrinkage and, in turn, increase the durability of infrastructures.

Crack width of concrete governs the penetration of external agents and thus the reinforcement corrosion rate. Self-sensing concrete, which often contains minor conductive ingredients like carbon fibers, should alert engineers of the crack widening by continually monitoring the change of electrical properties. In such fiber-reinforced cementitious composites (FRCCs), the crack widening is fundamentally controlled by fiber pullout (from matrix) behavior. In this study, single-carbon-fiber pullout tests were conducted simultaneously with electrical resistance measurement under direct current (DC), to couple the microstructure and electrical properties of the fiber-to-matrix interface. Both electrically non-conductive (w/o short carbon fiber) and conductive (w/short carbon fiber) cement matrices were tested. The results show that polarization resistance, which is an electrochemical effect that must be eliminated when quantifying the microstructure-related interfacial resistance, only existed in the non-conductive group. In the conductive specimen, the interfacial resistance monotonically changed with the fiber displacement during the debonding stage and the slippage stage; however, there was a drastic change of the resistance at the end of debonding (or the beginning of slippage), which for the first time reveals that the re-touching of the fiber and matrix is a transient process.

Building materials with piezoresistive properties are used in smart structures for the self-sensing and self-monitoring applications. The electrical properties of such composites are influenced by their composition, amount and type of conductive admixture, but there is also an effect of external conditions such as temperature and moisture. This study presents an investigation of the effect of water saturation degree and moisture content on the self-sensing properties of cement-based and alkali-activated slag composites with graphite conductive filler in compression. The results show that alkali-activated slag exhibits better piezoresistive response compared to cement-based composite. The moisture content has a slightly negative influence on the self-sensing properties tested composites as the gage factor decreased with increasing amount of moisture content.

The objective of this study is to reproduce, with large size laboratory concrete specimen, the non-uniform heating that is naturally observed in some civil engineering structures. The aim is to obtain a reliable predictive model, making it possible to evaluate the risk of developing certain pathologies such as Delayed Ettringite Formation (DEF) due to the temperatures reached and their distribution in the concrete.To this end, the dimensions and characteristics of the formwork were first determined from numerical simulations. Then, the formwork was supplemented with sensors to record the temperatures in the three spatial directions over time. The results showed that the sensors recorded a high temperature in the core of the specimens, exceeding 80 ℃, and that there were large temperature variations between the surface and the core of the concrete.

The determination of durability-relevant material resistances of concrete is of great importance. They serve as input to engineering models to predict the durability of structures under real environmental conditions. The natural resistances have to be determined in time-consuming experiments, since the processes in nature are very slow. This is particularly important for new materials where long-term experience is not yet available. Thus, accelerated testing is required. Only that way new materials can be evaluated regarding their durability and subsequently be used in practical applications. For carbonation, a new R3 accelerated test method is presented in this contribution. An automated carbonation pressure chamber was developed. It consists of a pressure vessel, automated in such a way that it can apply gas overpressure of various intensities up to 8 bar to mortar and concrete samples. Simultaneously, it can control and regulate the ambient CO2 concentration from 0 to 99.5% in a fully automated and continuously variable procedure. Experiments were carried out with varying combinations of gas overpressure at CO2 concentrations of 3 vol.-% to achieve the most time-efficient carbonation of mortars and concretes. Mortars with different material compositions were used to evaluate the general suitability of the test procedure with the developed equipment. The automated carbonation pressure chamber enables reliable carbonation testing with a total duration under accelerated conditions of only 7 days.

The permeability of hardened cement plays a crucial role in determining the durability of cement-based materials. In this contribution, we explore a novel approach to the study of small-scale porosity in cement pastes, and how its modification can affect the overall permeability. Experiments based on neutron dark-field imaging (BOA beamline – Paul Scherrer Institut) were designed with the aim of achieving a detailed and quantitative description of the pore structure in cement pastes. Paste and mortar samples were prepared with a water-to-cement ratio of 0.45. After curing in wet conditions, all samples were cut in slices of different thickness (2, 4, 6, 8 and 10 mm) to evaluate optimal neutron transmission conditions. Correlation length plots obtained from the dark field imaging signals are aimed to provide quantitative information on the pore network topology, which in turn controls the permeability of cement-based materials. This technique was preliminary implemented to the characterization of changes occurring within the pore network, in the presence of admixtures based on Cu-doped C-S-H nanocomposites, which were shown to induce a modification in the mechanism of C-S-H nucleation, promoting both an acceleration of early hydration kinetics and a reduction in permeability.

This paper describes the main features of the experimental in situ setups used to estimate the concrete deformability from six large Portuguese dams, all of which were built in the last 25 years. These experimental setups are commonly referred to as creep cells and aim at determining the modulus of elasticity for different ages and estimating the creep curve, under the same thermo-hygrometric conditions as the dam.Creep cells are composed of specimens of concrete with embedded strainmeters, placed in the body of a concrete dam during its construction, with a hydraulic flat-jack underneath. During the elastic modulus and the creep tests, while the jack introduces a given compressive stress in the specimen, the embedded strainmeters measure the subsequent strains, instantly or over time, for the modulus of elasticity or creep assessment, respectively.In recent years, there have been several developments in the design and in the installation methodology of this type of experimental setup, namely in Alqueva, Baixo Sabor, Ribeiradio, Foz Tua, Daivões and Alto Tâmega dams.The article also presents a brief compilation of the most important creep cells results for these dams, which are being used as an input to numerically evaluate the structure’s behaviour over time.

In the last decades major advances have been made in the development of self-healing concrete which is able to heal its own cracks without the need for traditional repair interventions, thereby increasing its durability and service life. Recently, more and more self-healing technologies have been applied in demonstrator projects. These demonstrator projects have made it evident that we need to develop new testing methodologies to evaluate the self-healing performance, as many laboratory test methods cannot be applied on structural elements on the construction site. In the current study different non-destructive test methods have been used to analyse the self-healing performance of concrete beams. These beams were cracked in a three-point bending setup. Part of the beams had a cast-in vascular network allowing the crack to be healed via the injection of polyurethane. The healed beams were compared to the reference beams without the vascular network by applying different test methods: microscopy, concrete moisture content, resistivity, air permeability, water permeability, and ultrasound. Based on the results of these methods which were obtained under laboratory conditions, it was found that the concrete moisture content and the resistivity only provided limited value in terms of conclusions for self-healing. All test methods were also applied to concrete walls on site. Based on this last measuring campaign, recommendations are provided for quantification of the self-healing efficiency on the construction site.

The EMM-ARM (Elastic Modulus Measurement through Ambient Response Method) allows the continuous monitoring of the elastic modulus of cementitious materials from early ages. The idea is to subject a beam, made of the specimen in its mould, to an excitation and monitor its response via an accelerometer. The excitation can either rely on naturally occurring vibrations, or on a controlled excitation system creating a signal with the necessary characteristics. The resonant frequency of the tested beam can be assessed with modal identification techniques, whereas the E-modulus of the tested material can be directly calculated with the dynamic equations of motion of the system.The original implementation of EMM-ARM uses specialized devices for the acquisition and excitation systems, which results in a relatively high price, as well as limited options for customization. The software used is based on proprietary systems (LabView), which further brings limitations on sharing for other institutions to use. On the other hand, one should bear into account that cyber-physical systems have shown significant evolutions in the last decade. Open-source platforms are increasingly popular and low-cost single-board computers are becoming widespread (e.g. Raspberry Pi). Electronic components have evolved parallel to these platforms, offering decent performances for low prices nowadays. The work hereby presented took inspiration from these cyber-physical systems to develop an open-source and cost-effective system able to conduct EMM-ARM tests independently from any other computing device. The system will be integrally presented as well as results obtained in comparison with the original implementation of the system.

Regulations on wastewater treatment (UWWTD-1991; WFD 2000) have evolved considerably over the past 25 years with the development of increasingly efficient bioprocesses that limit environmental risks. High-performance bio-physico-chemical wastewater treatment technologies were implemented for the plants of the main urban areas i.e. biofiltration, membrane bioreactors. Thus, over the last ten years, new types of degradation of concrete structures were observed in wastewater treatment plants, mainly in nitrification basins treating nitrogen compounds (ammonium) in effluents. The exact origins of these degradations are not yet determined.In order to understand the degradation mechanisms of concrete in nitrogen compound treatment basins, mortar specimens based on CEM V and CAC cements were exposed (i) in situ of one nitrogen treatment basin and (ii) in reactor for biological lab test. The design and implementation of the biological test were developed to reproduce were developed to reproduce nitrogen biological treatment and evaluate the degradation of mortars in a more controlled environment than the full-scale process. This laboratory test allows the evaluation of the biotic aspect of nitrification and in particular, the influence of acid production during biotic reactions and the influence of carbonates on mortar specimens.These two approaches allow highlighting the significant impact of the biomass and the modification of the environmental conditions at the biofilm/material interface.

The EMM-ARM (Elasticity Modulus Measurement through Ambient Response Method) methodology consists in using ambient vibration tests to monitor the E-modulus evolution of cement-based materials during hydration, right after casting. The dissemination of this methodology may have been hindered by the costs and proprietary platforms associated to the original test system. This work reports the development of a cost-effective and open-source test system to perform EMM-ARM tests, comprised of a data-acquisition system, accelerometer, and post-processing software. The development was supported by the Arduino prototyping platform and the Python program languages, both open-source resources. Being conceived to be an open-source hardware (OSH), full details are given on how to fully replicate the system. Validation was performed by comparing E-modulus estimates obtained from the proposed system and an original system used in previous works. The proposed system is shown to have a satisfactory performance to execute EMM-ARM tests, while being easily replicable, at a considerably lower cost, and offering high potential for further developments and customization due to its open-source nature.

During their service life, concrete structures are submitted to various types of boundary conditions among which thermal and mechanical loads are the most common. Thermal variations can be non-negligible in case of specific service conditions of the structures such as the storage of exothermic nuclear waste, or during some accidental conditions. Mechanical loading or moderate temperature can, independently from each other, induce high concrete deformations and cracking leading to a loss of serviceability of the structure. In the case of a simultaneous mechanical loading and heating or a heating of a previously loaded concrete structure, an additional deformation, called Transient Thermal Deformation (TTD), occurs. This phenomenon should be monitored because its kinetics and amplitude are significant. Since many concrete structures may be affected by TTD, investigations are needed to assess the coupled effects of different levels of mechanical loadings and heating on this additional deformation. This study presents a part of a wide experimental program dealing with the containment vessel behaviour of a nuclear power plant in case of a severe accident characterized by an increase in internal pressure and temperature. Concrete specimens were submitted to two levels of sustained stress, 30% and 60% of the compressive strength, using uniaxial compressive creep devices, and heated to various temperatures, 20, 40 and 70 ℃ under autogenous conditions representative of the core of the structure. TTD and the thermo-mechanical effects were analyzed through the strain evolutions of loaded and unloaded specimens.

The known tests to evaluate the post-cracking behaviour of fibre reinforced concretes (FRC) have some disadvantages. The most representative test of tensile behaviour, the direct tensile test (DT), is difficult to perform. Therefore, the use of indirect tests to evaluate the post cracking behaviour of FRC is common. Some of these tests are carried out in such a way that the samples are molded separately to the structure in prismatic shapes. This geometry makes it difficult to extract samples from the real structure to evaluate the behaviour of the FRC in the structure. Especially for the fibre reinforced self-compacting concretes, the fibre distribution and directions are strongly influenced by the shape of the structure and casting procedures, being important to use structural specimens, representative of the actual structure that the FRC is intended to be applied. This work proposes the use of a semi-circular bending (SCB) test for the characterization of post cracking behaviour of FRC. An experimental program was performed to demonstrate the use of the SCB test to characterize steel fibre reinforced self-compacting concretes (SFRSCC). Samples with small dimensions were extracted by means of a concrete core cutting machine. The results of the SCB tests were presented, and an inverse analysis was performed to obtain the tension behaviour of the SFRSCC. The results, obtained in terms of stress versus crack opening relationship, were compared with results obtained by DT tests. The results showed the potential of SCB test to evaluate the post-cracking behaviour of FRC, and the evaluated test seems to be particularly suitable for structural test specimens, extracted directly from the structure.

The current context of the climate change, exhaustion of natural resources and impetus towards circular economy is leading to an increase in the use of recycled aggregate concrete (RAC) in the construction industry. The French National Project RECYBETON investigated the feasibility of using recycled concrete aggregate (RCA) in concrete through studies of concrete’s properties, including microstructure and durability of RAC. This kind of project, transposed in the standards, allows to promote the advantages of the RCA use and an appropriate substitution rate in the concrete. Based on the previous knowledge, some characteristics of recycled concrete still require further investigation such as fatigue response.In that respect, an experimental protocol for compressive fatigue test has been developed in controlled laboratory conditions. This protocol was designed in order to monitor damage in the experimental samples during the fatigue compression test using various non-destructive methods (Ground-Penetrating Radar, modal analysis and Stiffness Damage Test). As a feasibility study, this protocol has been applied to standard concrete specimens first. The corresponding results obtained for standard concrete specimen submitted to a fatigue test are elaborated in this paper, including a comparative study of the considered non-destructive methods. This methodology not only allows to study mechanical characteristics of recycled concrete but also to monitor damage evolution over various cycles.

One of the most important tasks in the investigation of hydrated cement paste is the determination of the amorphous phase content, which is mostly cementitious gel. The determination of the cementitious gel content is important for the evaluation of the hydration process. However, this task is not trivial and it is hard to achieve high accuracy. The major approach for determining the content of the amorphous phase is by the use of an internal or external standard in the x-ray diffraction (XRD) analysis. This study compared two external standards, as well as two procedures of internal standard intermixing on amorphous phase determination accuracy. In addition, a novel method of calibrating the HKL phase for the Partial Or Not Known Crystal Structure method of evaluation of the amorphous phase using an internal standard was applied and evaluated. For this purpose, cement pastes with water to cement ratios of 0.30, 0.35, and 0.40 were prepared, and hydration was stopped using the solvent exchange at the ages of 7 and 28 days. The hydrated cement paste samples were examined using XRD and the hydrates assemblage and amorphous phase content were analyzed using Rietveld refinement. The bound water in hydrated cement paste was studied using thermal analysis. For comparison, the degree of hydration was determined by XRD, thermal analysis, and isothermal calorimetry. The experimentally determined amorphous phase content was compared with theoretical calculations based on the degree of hydration and the recommendations for the best amorphous phase quantification procedure were given.

Falling Weight Deflectometer (FWD) testing is a non-destructive method used to assess the condition of pavement structures. During FWD tests, a weight is let to freely fall upon the top surface of a slab, while a set of geophones located along the driving direction measure the deflections caused by the impact of the falling weight. These deflections serve as input for the back-calculation of subgrade properties. An unprecedented density of deflection data is obtained by means of multi-directional testing [1]. The present contribution refers to two original contributions. The first one refers to the presentation of experimental data from multidirectional FWD testing of one old and one new slab. The second original contribution refers to a structural analysis of the new slab, using a single slab model. In order to best-fit the measured deflections, a spatially uniform modulus of subgrade reaction and a spatially uniform eigendeflection are introduced as optimization variables. This strategy allows for reproducing the measured deflections very accurately, as quantified by a root mean squared error which is as small as 9.6 μm. This underlines that it is indeed possible to introduce a uniform modulus of subgrade reaction in the context of reliably explaining FWD deflection data, even when resorting to a single slab model, provided that a spatially uniform eigendeflection is accounted for.

In service conditions, reinforced concrete structures are multi-cracked due to the loads they are submitted to. It enables aggressive agents, such as chlorides, to penetrate the concrete cover and could initiate steel rebar corrosion leading to more structural damage. Some experimental programs focusing on chloride penetration were conducted on plain or cracked concrete, but mainly unloaded and unreinforced concrete specimens were used for the measurement. These tests highlight the linear dependence of chloride diffusivity to crack opening. However, they do not take into account the presence of rebar, and cracks are partially or totally closed up during the test, which is different from service conditions. This research project aims to understand the influence of micro- and macro-cracks on chloride diffusivity in conditions close to the service ones. To achieve this objective, three steady-state accelerated migration tests under electrical field are to be carried out on a same reinforced concrete specimen kept under a tensile load representative of a structural one. This non-standard chloride penetration test requires the adaptation of the experimental protocol. This paper presents preliminary adaptation work using numerical simulations developed with Comsol Multiphysics®. The impact of testing configuration and parameters, as well as cracking was investigated. Comparison of simulations and preliminary experimental results are also given.

The construction sector is one of the most energy-intensive and raw-material demanding human activities and hence contributes a significant share of greenhouse gas emissions. Therefore, making the construction sector greener is one of the main challenges for policy makers, private companies and the scientific community. To this aim, one of the most promising actions is based on recycling Construction and Demolition Waste (CDW) and converting them into secondary raw materials for the construction sector itself. On the other hand, the reduction of the environmental impact can be further amplified through the optimization of the production, assembly and deconstruction/reuse procedures as well as through the maximization of the service life.In this context, the present paper presents the main results of a research project aimed at exploring the possibility to define a concept for deconstructable buildings made by prefabricated modular Recycled Aggregate Concrete (RAC) elements. The concept is based on assembling duly sized and designed prefabricated blocks by means of a prestressing system based on an innovative memory®-steel technique. The target building typology is that of highly modular structures, which generally demand high construction speed and the possibility of reconversion of internal spaces. Several issues are targeted to achieve within the project activities: proper design of mixtures leading to durable RAC members, the most appropriate structural configuration, and assembling technique are considered for achieving deconstruction capabilities. A proof of concept is then designed, produced and tested.

Today, the application of various bio-based low carbon mortars leads to the use of complex multicomponent binding systems. Even if the hydration processes of the binders are known, the presence of organic particles and substances can alter the hydration kinetics and hydration rate of the mineral binder. Understanding and improving the hydration mechanisms of mineral binders in the presence of organic particles has the potential to improve the mechanical properties, hygrothermal performance and durability of bio-based building materials. Currently, there is a lack of knowledge about the effect of organic particles on the hydration of mineral binders, especially in the case of modern multicomponent binder systems. This work is devoted to the study of the effect of hemp particles and their derivatives on the hydration process of mineral binders. In this regard, two parts of experimental studies were conducted. First, the kinetics of hydration of lime-based mineral binder with hydraulic additives was investigated by microcalorimetric analysis. Secondly, a semi-quantitative X-ray diffraction tracking method was used to study the difference in hydration mechanisms of the studied multicomponent binder. The results highlighted the complexity of the influence of organic compounds on the hydration mechanisms of multicomponent binders. The results of the semi-quantitative hydration tracking method demonstrated the difference in the evolution of hydrates and allowed a better understanding of the hydration process.

Demolition and reconstruction of degrading structures alongside with the repetitive repair, maintenance, and renovation applications create significant amounts of construction and demolition waste (CDW), which needs proper tackling. The main emphasis of this study has therefore been placed on the development of concrete mixtures with components (i.e., aggregates and binder) coming entirely from CDW. As the binding phase, powdered CDW-based masonry units, concrete and glass were used collectively as precursors to obtain geopolymer binders, which were then incorporated with CDW-based fine and coarse concrete aggregates. Together with the entirely CDW-based concretes, designs were also proposed for companion mixtures with mainstream precursors (e.g., fly ash and slag) occupying some part of the CDW-based precursor combination. Sodium hydroxide (NaOH), sodium silicate (Na2SiO3) and calcium hydroxide (Ca[OH]2) were used at various concentrations and combinations as the alkaline activators. Several factors that have impact on the compressive strength results of concrete mixtures, such as mainstream precursor replacement rate, alkaline molar concentrations, aggregate-to-binder ratios and curing conditions, were considered and these were also backed by the microstructural analyses. Our results showed that through proper optimization of the design factors, it is possible to manufacture concrete mixtures entirely out of CDW with compressive strength results able to reach up to 40 MPa under ambient curing. Current research is believed to be very likely to promote more innovative and up-to-date techniques to upcycle CDW, which are mostly downcycled through basic practices of road base/sub-base filling, encouraging further research and increasing the awareness in CDW issue.

There has been an increase in the use of single-use plastic-based personal protective equipment (PPE) since the commencement of the COVID-19 epidemic in late 2019. As a result, clinical waste generation has increased significantly this as well as various environmental strains from excess waste ending up in landfill. Various recycling solutions are needed to reduce the environmental impact of disposal and incineration. This experimental study aims to examine the utilisation of single-use waste PPE generated from the coronavirus pandemic in structural concrete to aid in scaling back the volume of single-use waste ending up in a landfill. Single-use nitrile gloves, isolation gowns and face masks were separately added to aggregates at varying percentages of the volume of concrete. For the purpose of determining the effects of varying concentrations and materials on the mechanical properties and quality of concrete as well as the specific materials bonding performance within the cement matrix, concrete samples were subjected to compression strength and microstructural analysis. Results demonstrate steady trendy development across compressive strength results, with increases of 17%, 20% and 15%, respectively, across varying applications of waste PPE. At the same time, the results of the SEM-EDS analysis present an excellent bond formation amongst the materials utilised and the cement matrix. To the best of the authors’ knowledge there is a lack of existing studies that examine the feasibility of incorporating waste PPE into civil and construction applications, therefore, this study aims to highlight the novelty surrounding the topic for further research.

A novel treatment method for the improvement of recycled aggregates is MICP (microbial induced calcium carbonate precipitation), which is already used successfully in soil improvement. Recycled mixed aggregates (RMA), in particular, have limited use as they influence the performance of the concrete. The precipitation can be used as a surface treatment for the reduction of the porosity and water absorption of recycled aggregates. This study aims to compare three different MICP treatment methods to investigate their potential for the reduction of water absorption properties of RMA. MICP treatments such as spraying, immersion and an alternative MICP treatment using a Büchner funnel were tested and compared. The results show that all methods used were able to reduce the water absorption of the RMA. It was also found that multiple MICP treatments enhance this effect. In the process, the water absorption of the RMA could be reduced up to 42.8% (from 21% to 12%) after the third MICP treatment when using the immersion method with 24 h intervals. It was found, that due to the MICP treatments, the RMA requires less pre-wetting water for mortar production than untreated RMA. Also, layers of microbial precipitated CaCO3 could be detected on the surface of RMA grains.

The construction industry is the most resource-intensive sector. With a demand of 4.4 billion tonnes annually, concrete consumes, as the most used material in the world, a huge amount of resources. For the year 2050, an increase in demand of a further 25% is already forecast. The main components of concrete are materials whose resources are limited.With the use of textile-reinforced concrete, resources for concrete production can be saved compared to steel-reinforced concrete. The textiles used do not corrode and therefore, in contrast to steel reinforcements, do not have to be protected from external environmental influences with a minimum concrete cover. Thus, a low concrete cover is already sufficient, whereby up to 80% concrete can be saved.A high amount of energy is required to produce the new carbon fibres, so it is desirable to use these already existing fibre materials for as long as possible. It is already technically possible to separate carbon fibres from plastics. Studies show that recycled carbon fibres from carbon fibre reinforced plastic waste still have 80% of the original mechanical properties. A possible field of application for reuse of the recycled material could be in the construction industry. However, the production of inseparable material composites should be avoided. Therefore, the use of recycled fibre materials as textile reinforcement is being investigated in order to enable a separation of the composite components again at the end of the second life cycle of the carbon fibres.

Mine tailings are significant environmental liabilities worldwide. This adds up to the increasing depletion of non-renewable resources for use as construction materials. Valorization of such wastes as secondary raw materials is an effective environmental-friendly strategy. This paper presents an investigation on the valorization of low-grade sulphidic mining waste in the shape of cold-granulated artificial aggregates. The study was carried out in the framework of the NEMO project (EU Framework Programme Horizon 2020, Grant Agreement No 776846). Results reveal the efficient immobilization of heavy metals in addition to the possibility of partial replacement of aggregates in mortar mixes. The optimized granulation process, based on intensive mixing with minimal contents of cement as binder, was demonstrated in pilot production, and the artificial aggregate in sizes 0–4 mm and 0–10 mm was afterwards implemented in mortar mixes at replacement ratios of 17 and 32% of natural aggregate. Limited affectation of compressive strength and workability by the substitution with secondary aggregate was resolved through optimization of the superplasticizer dosage. The hydrated cement contained in the granules demonstrated no perceptible interference with the fluidifying action of the superplasticizer. The results reveal that despite their porous nature the granules are feasible to be used in non-structural or low-grade cement-based mixes. A notable contribution is therefore made for the valorization of the mine tailings as artificial granules with a comparable cement consumption to that required in landfilling.

Recycled concrete aggregates (RCA) heterogeneity, leads to different properties compared to the natural aggregates (NA), especially in terms of their water absorption (WA24). Moreover, the variability of these RCA properties is larger than the NA one. This is mainly due to the compositions of original concrete. These disparities in properties and their high variation range limit the reuse of RCA in concrete. In the construction industry, concrete production has a significant environmental impact. Indeed, the cement production induces high greenhouse gas emissions. Accelerated carbonation of RCA can combine the advantages of a capture of CO2 issued from plant and a reduction of water absorption of aggregates. Indeed, the carbonation reaction clogs the capillary networks of aggregates and then reduces the accessible porosity that directly influences the water absorption. To reduce global carbon dioxide emissions and to enhance the recycling of RCA, the French national project FastCarb aims to optimize an accelerated carbonation process at an industrial scale. This work is to study the evolution of RCA properties, issued from several batches, following treatment in a carbonation chamber with defined parameters. This paper analyzes the influence of accelerated carbonation and its efficiency on the evolution of the RCA absorption and its variability. In order to identify the influence of the composition of original concrete, RCA with various original concrete compositions were crushed then tested. It was shown that accelerated carbonation decreases RCA absorption but not its variability. Carbonation (evaluated by mass gain) and absorption reduction efficiencies are not directly correlated.

The performance of mould release agent (MRA) has direct effect on the surface properties of concrete, and this eventually affects long-term durability. Currently, the most utilized MRA are from petroleum origin. But they are not eco-friendly and causes health hazard during application. Thus, eco-friendly bio-based wax emulsions are required. They have the potential to mimic the properties of petroleum-based releasing agents and thus could apply as mould-release agent that meets market requirements which has a low health risk and low climate impact. This work examined two bio-wax based MRA (F1 and F2) and compared their performance with commercial bio-based and petroleum-based MRA. The interfacial properties between MRA and formwork (steel, sawn wood and plywood) surfaces were evaluated using contact angle and surface tension measurements. Similarly, capacity of MRA to demould the concrete from formwork (steel and plywood) was measured using controlled tensile pull-off experiments. In addition, influence of MRA on surface appearance of concrete was analysed using image analysis and visual inspection of colour uniformity.The results indicated that for plywood and steel, F2 MRA showed higher adhesion energy compared to F1 MRA suggesting F2 could have good applicability for vertical and horizontal formwork surfaces. Furthermore, F1 MRA and F2 MRA reduced adhesion for low alkaline cement concrete at steel and plywood surfaces, whereas for regular alkaline cement concrete, they effectively reduced adhesion at plywood surface compared to steel surfaces.

To limit the environmental impact of the construction sector, including the need for natural resources, new materials using co-products from other industries need to be investigated. At the same time, the aquaculture industry produces a large number of seashell co-products that need to be reused or discarded. Some researches were carried out on using seashell co-products as aggregate replacement in concrete but mainly focused on the workability and mechanical properties of seashell concrete. Thus, interrogations remain on their durability properties. This paper investigates the durability properties of concrete with a high substitution rate of aggregates by seashell co-products. Concrete with the same mechanical resistance and workability was developed with a replacement ratio of aggregates by oyster shell up to 50%. Two different types of cement were investigated: a reference Portland cement (CEM I 52.5 N) and another cement with a high blast furnace slag content (CEM III 32.5N). Over six months, the evolution of concrete's chloride resistance was studied using durability indicators such as porosity accessible to water, resistivity and apparent chloride diffusion coefficient. At the same time, the gas permeability of concrete after six months of curing was investigated under different degrees of saturation. The first results show better durability properties for concrete, including oyster shell aggregates and higher gas permeability linked with a higher porosity accessible to water. This durability improvement is increased with cement including blast furnace slag.

The considerable development of the textile industry contributes to the fact that the production waste generated in the manufacture of yarns and fabrics is constantly increasing. These are so-called “pure wastes”, that, as a rule, never reach the consumer. Examples of such waste are weaving machine waste, products with a manufacturing defect, etc. Surveys in the technical textile industry have shown that only a few manufacturers use these wastes in their production, while they mostly end up in landfills. In Croatia alone, 300 tons of these wastes are generated annually, which indicates that the available quantities are sufficient for use in the construction sector and thus represent a valuable resource for the production of construction materials.High-quality fibres can be obtained from these wastes, which can be used as reinforcement in cementitious composites. However, it is critical to analyse the potential waste fibre streams, characterize the available production waste fibres to determine any initial flaws, the surface treatment processes used in relation to their original purpose, and finally the resistance to the alkaline environment. This paper provides an overview of available production waste fibres, their properties, and challenges for future use in cementitious composites.

With the increasing awareness of global warming, largely due to the emission of large amounts of CO2, some attempts have been made to develop strategies to help combat the growing trend of global warming. To reduce the harmful effects of concrete production, efforts are being made to reduce the amount of cement used by replacing the cement with mineral additives to maintain or improve the properties of the concrete. In addition, the use of waste materials as substitutes for cement and other concrete constituents is being promoted and investigated. This paper presents an experimental study on the influence of ash from wood biomass (used as a cement substitute up to 30%) and the addition of recycled polymer fibers from waste rubber in an amount of 2 kg/m2 (used as a substitute for industrial polypropylene fibers) on the residual mechanical and durability properties of concrete exposed to high temperatures up to 600 °C. In addition, reference concretes were prepared using only cement and industrial polypropylene fibers for the comparison purposes. A total of 5 different mixes were tested. The following tests were performed on the concrete specimens before and after thermal treatment: compressive strength, static modulus of elasticity, ultrasonic pulse velocity and gas permeability. These properties represent the input parameters for the evaluation of the condition of reinforced concrete elements after exposure to fire. The obtained results show that the use of the investigated waste materials in concrete leads to comparable or slightly better properties after fire exposure compared to the reference concrete.

The reduction of fly ash deposits due to the near-future shut down of lignite consumption power plants orients the Engineered Cementitious Composites (ECCs) research to partially replace this by-product by other fine-grained wastes. Lime powder from marble industry has been studied in high modulus of Elasticity PVA-ECCs by acting as binder and/or sand replacement. The present research investigates the mechanical behaviour of a strain resilient CC made by low modulus of Elasticity PP micro-fibers (12mm in length) where the fly ash is replaced by the lime powder (LP), using as reference mix the C1FA2S1.1 (C denotes cement, FA fly ash, S sand and the subscripts the per weight contributions in the mix). Examining several scenarios on trials where LP totally replaced the fly ash (C1LP2S1.1) or both the fly ash and the sand (C1LP3.1) or the fly ash and the latter the cement (FA1LP2S1.1) led to the optimum mix C1LP2S1.1 in respect to adequate mechanical properties. This mix is mechanically investigated by conducting a series of simple tests (compression, bending, splitting). The difficult direct tension test is elaborated in the compression machine by interpolating a specially designed metal strut apparatus where the embodied dogbone specimen acts as the tie. The experimental results are analysed aiming to correlate the mechanical properties obtained from different test setups and discussed aiming to answer whether this novel material is appropriate for structural use.

The main problem of the sulfate attack topic is the understanding of the so-called physical sulfate attack. However, the current existing testing methods are not suitable for sulfate attacks under arid conditions. A new uniaxial approach is established to investigate sulfate attack by combining these two aspects into one single sample. The different behaviours after sulfate exposure with this uniaxial penetration approach are compared with various cement materials. Portland Cement (PC), Sulfate-Resisting Cement (HS), and Limestone Calcined Clay Cement (LC3) show different levels of sulfate resistance: PC is quite susceptible to ettringite-type attack and causes expansion and cracking LC3 cement show negligible expansion and cracking but accordingly potential to salt crystallization attack due to the sulfate ingress from the capillary rise and crystallization from drying. The damage of spalling due to Na2SO4 salt crystallization is dependent on the exposure conditions (constant RH and temperature). Results show that expansive force is from the ettringite crystallization pressure in the confined space (radius < 50 nm) within C-S-H gel with a supersaturation, damage from salt crystallization pressure only happens potentially once the water evaporation rate is faster than the capillary rise.

Chloride ions (Cl−) are deleterious to reinforced concrete structures because they promote rebar localized corrosion. This may have detrimental effects on the rebar section and on the static behavior of the entire structure. Accelerated tests to simulate the entrance of chlorides may give some indications on the durability of cement-based infrastructures. A possible test consists of applying an electric field with a voltage of 20 V for 24 h on both side of cylindrical concrete specimens. A chloride migration coefficient is measured out of five samples. This is largely related to the porosity of the materials, although the interactions among the chemical species within the cementitious matrix may significantly influence the test results. In this work, several cement pastes were prepared by using different type of cements, partially added with supplementary cementitious materials. The samples were exposed to the electric field. The penetration depth was detected by spraying a Silver nitrate solution on the broken specimen surfaces by means of a visual and a SEM inspection. The chloride migration coefficients and the porosity of the samples were also determined. In this manner, it was possible to observe that the porosity of the cement pastes was not always correlated with the chloride penetration depth. The chemistry of the cementitious material and their binding capacity with respect to chlorides also play a significant role in the forced penetration under an electric field. The pore interconnectivity and the conductivity of the pore solution also play an important role.

Higher availability of grand granulated blast furnace slag compared to coal fly ash has attributed lots of attention to this supplementary cementitious material in recent years, especially with respect to applications in infrastructure. Therefore, further research on long term performance of slag containing binders in chloride containing environments is promoted.In this article chloride binding in a high slag containing composite binder (70% substitution) with respect to the changes in structure of CSH gel prior and after exposure to chlorides and its effect on chemical and physical chloride binding is accounted for. The changes in the structure of CSH are accounted by NMR analysis and the effect of these changes on chloride binding is addressed through adsorption tests. The results are compared with a ternary binder of cement-silica fume-metakaolin, given the relatively similar chemical composition between these two composite binders, as well as a reference Portland cement binder.The results infer that the slag containing binder exhibits higher chloride binding capacity compared to the metakaolin-silica fume containing. Moreover, a higher share of chemically bound chloride (meaning a lower physical binding) in SCM containing binders is foreseen compared to pure Portland cement system, due to the increased C(-A)-S-H chain length and Al/Si molar ratio in these binders. Furthermore, it is shown that exposure to NaCl causes a higher share of chemically bound chlorides compared to the CaCl2 exposure while the total bound chloride content increases upon exposure to CaCl2.

Chloride bulk diffusion is generally analysed with apparent diffusion coefficients fitted on full chloride penetration profiles, which are resource intensive to obtain with the grinding and titration method. As part of a comprehensive project on chloride ingress in blended cement pastes, this paper employs a dataset including a wide range of systems with 6 different types of binders and 3 different water-to-binder ratios. More specifically, bulk diffusion experiments were performed on cement paste specimens exposed to a 0.5M NaCl solution. Chloride profiles were then obtained on cross-sections by micro-X-ray fluorescence after 6 months, 1 year and 4 years of exposure. Results indicate that, for the classification of chloride penetration resistance using bulk diffusion results, the apparent diffusion coefficient Dapp fitted over the whole profile could be replaced by XCr/√t (the penetration depth for a specific reference chloride content divided by the square root of time). For reference chloride contents (Cr) in the lower half of the measured profiles, √Dapp was highly correlated with XCr/√t (R2 = 0.93–0.99). Thus, measuring chloride penetration depths (e.g., using a silver nitrate spray) after different times of exposure to chloride concentration typical of seawater may be a simpler classification indicator than the conventional profile fitting of bulk diffusion results (which needs grinding and titration).

In this paper the Tang’s model (Cem. Concr. Res. 1999), updated by introducing the pore geometry factor, was calibrated on through diffusion (steady-state) test results obtained from literature. This enabled to propose a new improved approach for estimating the intrinsic friction parameter ψ, that accounts for concentration dependent ionic interactions in cementitious materials pore solution. Uncertainties in multi-parameter estimation from the bulk diffusion (transient) tests are discussed. In the steady state diffusion test, the chloride binding effects can be eliminated, enabling to estimate the instantaneous (Fick 1st law) diffusion coefficient (DFick1). The measured dependency of DFick1 as a function of (upstream) concentration, enabled first to calibrate the pore geometry factor (comprising apparent tortuosity and open porosity) at infinitive dilution extrapolation. Finally, the calibrated friction parameter ψ was found to be 1.9 times higher than for NaCl pure solution, in contrast to previously reported values that were factor 21 to 32 (calibrated on bulk diffusion test) or even 100 to 1000 times higher, which are related to uncontrolled interferences with the other parameters. The contribution of individual factors that affect the DFick1 dependency on chloride concentration is quantitatively discussed.

A self-sufficient multi-species and multi-mechanism reactive-transport modelling framework for concrete is presented. The modelling framework is “self-sufficient” as its input data only include the chemical composition of the cementitious materials (e.g., cement, supplementary cementitious materials, etc.) and mixture proportions of the analysed concrete (e.g., water-binder ratio, aggregate content). The approach allows the calculation of transport properties of concrete using the formation factor of concrete, which can be calculated using the recently developed pore partitioning approach for concrete. This approach extends the Powers-Brownyard model to include concrete incorporating supplementary cementitious material and combines it with thermodynamic calculations to obtain electrical properties of concrete. These thermodynamic calculations predict pore solution composition, pore solution resistivity, pore volumes, and reactions between the solid and ionic components of the cementitious matrix such as pozzolanic processes, hydration, and chloride binding. The framework allows the solution of reactive-transport equations with minimal input data that is easily accessible to assess key transport questions related to service life such as ionic movement, chloride ingress, and time to corrosion. The approach eliminates the costly need to determine the transport properties of concrete experimentally, which are, in most cases, inaccurate because they do not represent the actual transport mechanisms that are intended to be simulated. This modelling framework has the potential to be used in conjunction with performance specifications currently being developed in the United States.

The prediction of chloride ingression in cement-based material has gained a great deal of interest among researchers as it causes long-term structural damage in buildings by chloride-induced reinforcement corrosion. The Cl− diffusion in mortar is influenced by internal factors including pore-structure and hydrates which are determined by clinker properties, mixture recipe, and curing conditions and exposure conditions. The Cl− penetration in mortar leads to the modification of the microstructure and pore-solution due to the disequilibrium of the hydrates-pore solution system. Considering the complexity of the process by incorporating all aforementioned factors and interaction of Cl− with hydrates, a new model is herein proposed for predicting the microstructure of the mortar during the Cl− diffusion. In this work, the microstructure of mortar is considered as a three-phase material: aggregates, interfacial transition zone (ITZ) and bulk paste, and ITZ is realistically considered as high W/C paste compared to the initial W/C. The developed COMSOL-IPHREEQC model involves hydration model for calculating the dissolution of clinker in bulk paste and ITZ, thermodynamic model including the surface complexation model to predict the hydrates and the Cl− adsorption by hydrates, homogenization approach to compute the average hydrates, porosity, pore solution composition and diffusion parameters of the mortar and COMSOL Multiphysics to perform the transportation calculation. The predicted results are validated with experimental results available in the literatures to verify the reliability of the proposed model. The effect of ITZ on the penetration of Cl− is also assessed in this work.

Salt crystallization belongs to the main decay processes in historic masonry mortars in which lime-pozzolan binders were often used. In this paper, the resistance to salts crystallization, their accumulation, and the microstructural changes of lime mortars with five different natural pozzolans are thoroughly investigated. Natural, fine ground, thermally untreated pozzolans (chalcedonite, pumice, zeolite, spongilite, and lava) were used as a partial replacement for lime in the amount of 10%, 20%, and 40%. The salt crystallization resistance of mortars were determined using Na2SO4, NaCl, and NH4NO3 solutions. The microstructure of the mortars after the testing was monitored with a scanning electron microscope, the accumulation of anions in the mortars was determined by chemical analyses and mass increases, and the formation of new minerals was confirmed using X-ray diffraction analysis. Nitrates were most accumulated in mortars with lava, sulfates in spongilite mortars, and chlorides in mortars with chalcedonite. Both crystalline and amorphous neoplasms were observed in the microstructures of mortars, the most common being nitrocalcite, cesanite, gypsum, ettringite, and hydrocalumite. The results showed that different natural pozzolans are a bit more suited to different saline environments and it should be considered when using them.

The coastal areas contain high concentrations of chlorides and other corrosive agents which frequently extend far from the shoreline. Together with wetting-drying cycles caused by wind, rain, tides, etc., these concentrations lead to severe degradation and loss of durability of marine structures. The current study focuses on durability of the parapet beam made of reinforced concrete as a part of the wave breaking structures in the Haifa Bay Port, Israel, and includes durability-related observations and measurements conducted both in situ and in the laboratory. To determine the corrosion potential of reinforced concrete, the study followed the guidelines of the ASTM G-109 and ASTM C-876 standards. A part of the samples cast in the laboratory contained artificially made cracks of different depth (½ and one cover thickness), while another part of the samples was crack-free. The accelerated durability tests in the lab included exposure to the saltwater combined with wetting-drying cycles. It was concluded, that on the one hand, in the presence of small cracks which even did not reach the rebars, using migrating corrosion inhibitor did not show satisfactory results in terms of steel protection and even increased the corrosion risk. On the other hand, in both non-cracked parts of the parapet beam and laboratory samples, migrating corrosion inhibitor did provide effective corrosion protection. This result is significant for assessment of durability of cracked reinforced elements made of concrete containing migrating corrosion inhibitors, because cracking in concrete occurs frequently, and its existence is confirmed and considered by the building codes.

To boost the usage of non-ferrous metallurgy slag (NFS) into alkali activating material (AAM), durability analysis of NFS-based AAM is needed. For this purpose, the dissolution behaviour of NFS-based AAM in sulphuric acid was investigated. In order to answer the question whether unreacted slag in the NFS-AAM structure is the weak part during acid exposure, dissolution experiments were conducted both on raw NFS and NFS-based AAM paste sample. The results suggested that both NFS and reacted binder dissolve in sulfuric acid. The dissolution of the raw NFS was, however, significantly faster and to a greater extent than that of the AAM paste. For the raw slag, almost all Si and Ca were detected in the solution, while about 80% Fe and Al were dissolved after exposure to sulphuric acid. The lower values, compared to Ca and Si, could be due to the undissolved crystal phases or precipitation. For pastes, 88% Ca, 79% Fe and 75% Al ended up in sulphuric acid solution, while only 60% of Si was dissolved. This corresponds approximately to 100% minus the reaction extent of the slag, suggesting low Si dissolution from the AAM binder. This can be explained by the presence of a highly polymerized silicate network with high acid resistance. The results confirm the importance of the slag structure and reacted amount of slag on the sulphuric acid resistance of NFS-AAM. The findings here are instrumental in providing solutions to improve sulphuric acid resistance of NFS-AAM.

Monitoring early-age elastic properties of concrete is critically important for accurately determining the crack risk. This paper focuses on evaluating the dynamic elastic moduli in high-performance concrete at early age. Firstly, a comprehensive set of reliable test data for dynamic elastic moduli was presented. Then, a comparative experimental investigation for assessing the static and dynamic elastic moduli values was put forward. Thirdly, the influence of curing temperature on static and dynamic elastic moduli was investigated in depth. The temperature sensitivity of static elastic moduli values seems lower than that of dynamic elastic moduli values. Importantly, the influence of sustained tensile stress on static and dynamic elastic moduli was examined. It was observed that the static elastic moduli values were more sensitive to sustained load when compared to the dynamic elastic moduli evolution at early age. Based on the newly measured test data, the possible underlying mechanisms behind such evolutions were explored.

The requirements to fill and solidify boulder ground such as rubble mounds for the purpose of seismic retrofitting of an existing revetment structure and deepening of existing gravity-type quay wall is necessarily needed. In our pervious study, we had developed the optimum grout material to solidify the rubble mound foundation. However, a challenge appears when the foundation structures are in underwater. When the grout material is extruded downward during filling, the grout material is detached by gravitational force. A recent study investigates the suitability of grout material called plastic grout, which has anti-washout under water and corresponds to Bingham plastic as a rheological property, for filling and solidifying boulder ground in underwater with higher quality. Moreover, this study also investigates the optimum mix proportion of plastic grout material as a filling material for boulder ground in water. This study shows that it is desirable to use a mix proportion that suppresses the phenomenon (a mix proportion with high tensile strength in water). Moreover, this study confirms that the tensile strength increases by substituting a part of cement with silica fume and mixing with bentonite. Furthermore, it was shown in the study that the developed formulation can be appropriately evaluated by vane shear strength, pressurized bleeding rate, and cylinder flow value (static, dynamic).

Terrorist attacks increased manifold in recent times leading to the loss of lives of military personnel and civilians. Blast and Ballistic attacks can cause failure of structural components or structures. On the other hand, Electromagnetic pulse (EMP) could disrupt electronic and communication systems creating a threat to the nation’s defense. In this regard, an innovative concrete (Multi-Faceted Engineered Concrete (MFEC)) was developed through rational selection and proportioning of materials to mitigate Blast, Ballistic and EMP attacks. The developed concrete was tested for mentioned forms of attacks at laboratory scale using a shock tube for blast, a single-stage gas gun for ballistic and an EMP concrete test chamber for EMP resistance. The developed concrete exhibited excellent mechanical properties, energy absorption capabilities along with conductive and absorptive properties. The engineered concrete can be used in the construction of civil and military infrastructure to impart better protection against a multitude of disasters rather than protection against one type of disaster, leaving the infrastructure vulnerable to others.

The durability of a concrete structure ultimately depends on the quality of the cast concrete, whereby especially the edge zone of the manufactured concrete segments is crucial for environmental exposures. In order to ensure that the concrete provides sufficient resistance to these exposures, the corresponding material properties must be quantified according to the so-called performance-based durability design. However, the quantification of these properties is carried out using mainly standardized concrete test specimens, cast and cured under optimized laboratory conditions. On the other hand, the real structure is built under different in situ and curing conditions. This may lead to a deviation of the concrete properties achieved at the construction site in contrast to those determined in the laboratory.In this context, systematic investigations were conducted to assess this deviation. To accomplish the studies, separately manufactured test specimens, as well as dummy walls (4 m2), were cast at different construction sites. The separately manufactured test specimens were cured in the laboratory following current standards. The wall was cured in its formwork for a defined number of days (mostly 7 days). Subsequently, drill cores were taken and compared to the laboratory samples in terms of the corresponding material properties (compressive strength, chloride migration and carbonation rate of the concrete). As a result, the core drill samples underperformed the laboratory-cured samples, indicating that the performance achieved at the construction site tends to be lower than that of laboratory specimens.

Currently, we expect a wider development of modern concrete mixes in the construction industry, such as concretes with alternative cement types and binders, recycled aggregates but also concretes with dispersed fibre reinforcement, in order to accelerate our efforts to reduce greenhouse gas emissions and to increase the service lives of built assets. In fact, steel fibre reinforced concrete is now gaining in applications such as industrial floors, slabs, and tunnels and it is being introduced to the next generation of Eurocode 2. A well-established fastening method is direct fastening by use of powder actuated fasteners (PAF), which bring along several benefits in terms of speed and ease of site work. However, due to the significant variability in the installation and load-bearing performance of such fasteners, particular focus needs to be diverted to the reliability characteristics and a redundancy-based design approach. The objective of the presented study is to provide fundamental engineering concepts for direct fastenings and to share and discuss the first worldwide experimental results on the performance of PAF in steel fibre reinforced concrete. The conclusions enable a comparative assessment for different fastener types and fibre types and content allowing for useful conclusions for the design and they provide a substantial reference for future research and applications.

In France, buildings’ heating systems represent 45% of the total energy consumption and are responsible for 27% of greenhouse gas emissions. Thermal insulation, including the External Thermal Insulation Composite System (ETICS), has a big impact on energy consumption and CO2 emissions, increasing, at the same time, the thermal comfort of the residents and decreasing their energy bills. The fiberglass mesh-reinforced rendering mortar is used as the external protective layer of ETICS. Many defects may attain the ETICS, including the cracking of the rendering mortar. The cement-based mortar undergoes chemical, thermal, and hygral strains, which, when restrained, cause stress that may attain the material’s tensile strength and cause the mortar to crack. The fiberglass mesh is proposed as a reinforcing solution for cracking. Here, we focus on the cracking development in the reinforced mortar layer using experimental techniques. To understand the crack initiation and propagation in the reinforced mortar layer and the role of the fiberglass mesh as reinforcement inside the mortar, a new mechanical inclined 4-point bending set-up is developed and performed using in-situ X-ray tomography. The latter allows observing the cracks inside the mortar sample, shedding light on the reinforcement mechanisms of the fiberglass mesh and its impact on the initiation and propagation of the cracks.

Reinforced Concrete (RC) structures behaviour depends strongly on the variability of materials properties. This variability can be considered at different scales as concrete is a heterogeneous material constituted of several phases including different shapes, sizes and types of aggregates. In addition, at the structural level, the properties of concrete are highly dependent on the pouring process and exposure conditions. Thus, in order to evaluate the mechanical behaviour of RC structures in a reliable manner, the consideration of the spatial variability is important. The objective of this work is to study the effect of this spatial variability on the failure behaviour of a RC wall subjected to shear loading. A constant vertical and uniformly distributed compressive load is applied on the upper part of the wall and the shear loading is imposed by a horizontal displacement. A numerical approach based on Monte-Carlo simulations and Fichant’s damage model is considered. Several simulations were thus carried out in 2D to study the effect of the correlation length and standard deviation of Young’s modulus (E) and tensile strength (ft) on the failure behaviour. The spatial variability of concrete properties was generated using the Circulant Embedding spatial discretization method. The results show that the coefficient of variation of the peak load and the corresponding displacement increase with the increase of the considered correlation length and standard deviation for E and ft. In addition, the spatial variability affects the damage fields and cracks openings and plays a major role in the localization of shear damage.

The utilization of cementitious materials in deep sea areas has been planned to construct the platforms for diastrophism monitoring, geoneutrino observation and offshore wind power generation. The authors have studied the behavior of the hardened cementitious materials at deep sea such as damages by chemical degradation, hydraulic pressure, and their combination. However, casting of fresh cementitious materials at deep sea floor could also be required to joint precast members in-situ. In this study, the first-ever casting test under deep sea with depths of approximately 1000–2000 m by using a deep-submergence research vehicle and remotely operated vehicle was shown. A unique cement injection kit was developed for the deep-sea test, whose binder contained a specific calcium aluminate cement and retarder. Moreover, the hardened specimens of the specific binder were exposed to deep sea conditions for one year. The corresponding changes in technological properties of the exposed specimens such as strength and dimensional stability could be explained through our previous studies and the results of thermodynamic calculation.

In the top-down construction method, structural columns are embedded in concrete piles. Axial force is transmitted to the concrete pile through the following: bond resistance between steel column and concrete pile, shear resistance of stud-connectors, and bearing resistance at the bottom of the embedded area.The steel column embedded concrete pile head design contributes not only to the construction axial force but also in some cases to the concrete pile compressive strength. Adopting an open-section steel column, such as an H-shaped cross section, results in a small defect cross-section of the concrete pile with relation to the column within the embedded area, whereas adopting a closed-section steel column (CFT; concrete filled steel tube, etc.), the defect cross-section becomes large. Therefore, with closed-section steel column, the embedded area reaches the limit of its concrete pile compressive strength before the not-embedded area, resulting in risk of fracture.The concrete pile head is usually arranged with reinforcing bars to prevent splitting near the bottom of the embedded area for the purpose of ensuring strength. However, there are few studies verified experiment and analysis of the previous research for calculating the amount of reinforcing bar both domestically and internationally.For CFT column, using the amount of reinforcing bar and the pile diameter as parameters clarifies the relationship between the amount of reinforcing bar and axial strength in structural experiments. The resulting data is used here to propose an evaluation formula for the amount of reinforcing bar necessary to ensure the concrete pile axial strength.

Bridges play a vital role in highway transportation systems and damage to bridges may cause impaired emergency response and economic loss and interrupt the functionality of the systems. Damage to bridge during the last earthquakes shows that considering the effects of the vertical component of earthquakes in seismic damage assessment of reinforced concrete (RC) piers is of great importance. This paper aims to assess the probability of damage to RC columns under the simultaneous effect of three earthquake components. For this purpose, two damage indices including strain and curvature ductility have been used and the fragility curves of RC columns have been developed with Probabilistic Seismic Demand Models (PSDM) under a series of ground motion records. Moreover, the variation of axial force, bending moment, and shear force have been investigated. The results show that considering the vertical excitation may increase the probability of different damage states of RC columns, particularly in higher damage states.

Pumped storage hydropower (PSH) plants are storage energy systems that represents one of the most sustainable, economical, and efficient solutions for energy storage, being an excellent alternative to store energy from intermittent sources such as wind and solar. This paper presents an early application of numerical modelling as a tool to verify new conceptions and constructive methods for PSHs checking the possibilities of using 3D printing. The use of such technology for concrete has gained rapid development in recent years due to the advantages in structural optimization and economy with formwork in conventional construction. Practical engineering applications have proven the applicability of 3D printing in large-scale construction of building components and massive structures, and compared to conventional manufacturing methods, this advanced technique has several advantages and offers almost unlimited potential for geometric complexities. We explore new design conceptions with the help of numerical modelling in two ways: (i) during the early ages considering the phenomena of hydration; (ii) after hardening of concrete verifying the integrity of the structure. The results indicated that numerical modelling can point to new solutions that will help address the challenges posed by greater sustainability in energy generation and storage in the 21st century.

The article presents a study of the interface performance of precast prestressed composite beams. The main objective of the research program is to determine the influence of the interface's shape on the composite element's behaviour. The rib-shaped precast prestressed beams with full bond, broken adhesion and broken contact were tested. DIC measurements with force-displacement relations analysis showed a crucial impact of cracking length on element performance. The formation of the local slip of the interface was related to the propagation of bending and shear cracks. The crack reaching the support zone should be considered the moment of debonding of the composite element. Based on numerical and analytical studies, it can be concluded that the adopted friction coefficient correctly represents the behaviour of the interface. The presented numerical analyses will be extended and correlated with the following parameters: cohesion, friction, the soft-hard function of the interface and the strand bond slip.

Civil infrastructure is crucial for economic growth and prosperity. It is important to emphasize that a crisis situation exists in civil infrastructure, specifically public transportation infrastructure. As a result of aging, severe environmental conditions and deferred maintenance decisions, assets continuously deteriorate. Decisions related to infrastructure maintenance and rehabilitation depend not only on an asset’s current condition, but on their predicted performance behavior with time as well. Infrastructure systems management plans consist of assessing the performance of the different components, predicting future performance of the components, then integrating the performance of the components into one performance of the system. Previous research has developed structural performance curves using reliability-based cumulative Weibull function for individual components of reinforced concrete infrastructure. This paper focuses on developing series and parallel system modeling techniques in order to construct structural performance or service life curves for the whole infrastructure system. The model is applied to subway stations and tunnels. Data are collected from the Société de Transport de Montréal (STM) inspection reports. The developed model is applied to a network segment of the STM subway network. Results show that system deterioration rates are between 2% and 3% per year. The remaining useful service life is predicted to be the year 2076 for renovated stations. This research is relevant to industry practitioners and researchers since it develops service life curves for subway stations and tunnels as typical infrastructure systems.

Durability is one of the main uncertainties of reinforced concrete structures. Moreover, one of the main causes of the reduction of this durability is the corrosion of reinforcement. In the literature, several authors provide mechanisms and models that allow predicting the behaviour of structures. However, due to the very heterogeneity of the structures and the dispersion of the parameters taken into account in the models, it is necessary to calibrate or validate these models with direct measurements on the structures or, more precisely, the monitoring of durability-related parameters. Additionally, monitoring structures allow decisions to be taken at early stages and even before any pathology occurs.Since 1995, a mockup has been monitored at El Cabril, Cordoba (Spain), where sensors for temperature, deformation, corrosion potential, resistivity, oxygen availability and corrosion rate have been installed. The data have been analyzed and filtered using machine learning algorithms.The analysis of the data obtained during these years allows us to appreciate the evolution of the different parameters and their daily and seasonal variation. The sensors that were successfully installed are still active. To date, no corrosion problems have been reported in the structure.

Due to the increasing difficulty of bridge maintenance, bridge monitoring is used increasingly to detect damages at an early stage.This paper deals with the development of a low-budget monitoring system for expansion joints. The aim of this paper is to select the hardware of a low-budget monitoring system, create an artificial neural network model, that can distinguish between a good and a broken expansion joint and finally transmit the data set to a dashboard in a web application.The idea is to record audio data directly under the expansion joints using a microcontroller. For the selection of the right hardware, two microcontrollers were tested, on the one hand Arduino Nano 33 BLE Sense and on the other hand Arduino Portenta H7 with Vision Shield. Then the audio samples are uploaded to Edge Impulse and the data set is assigned to two classes: good and damaged. An artificial neural network is then created in several steps, starting with the creation of a so-called impulse, testing the model and loading the model onto the Arduino device. The results of the monitoring system are transmitted to a dashboard in a web application in real-time.

Corrosion is one of the main deterioration phenomena in reinforced concrete structures. This paper investigates the correlations between localized pitting corrosion and measured performance indicators in reinforced concrete beams subjected to sustained relative deflection and accelerated corrosion through impressed current. Strain measurements from distributed optical fibre sensors were used to calculate the deflection, crack distribution and crack widths over time and thus to quantify changes in performance indicators with corrosion. Once the accelerated corrosion test was concluded, the steel reinforcement bars in the region affected by corrosion were carefully extracted and 3D laser scanning was carried out for the assessment of the reinforcement corrosion. More specifically, laser scanning results were used to identify the localized pitting regions in the vicinity of transversal cracks and consequently the total amount of steel corroded in the same. By assuming the following three hypotheses: (i) an effective pit length at the cracks, (ii) at the beginning of the corrosion process all the applied current and consequently all the corrosion was localized at the pits, (iii) any variation observed in the deflection is attributed to corrosion, therefore proportionality between deflections and loss of steel exists. The total corroded volume of steel was calculated and later compared to the 3D scanning. The results revealed that the volume loss in the pits calculated using Faraday’s law and the proposed method was in very good agreement to the direct volume measured by means of the 3D scanning. Consequently, a direct relation between corrosion and deflection could be established.

In the way towards a carbon neutral construction industry, the partial substitution of cement clinker by alternative binders is becoming increasingly popular in the design of low-carbon concrete mixes. However, as new concrete mixes are developed, the parameters governing the risk of early-age cracking arising from restraint forces due to thermal and shrinkage deformations need to be investigated for each mix. This paper reports the results of a field test in which distributed optical fiber sensors (DOFS) were used to monitor strain and temperature in two large-scale prisms cast against the ground. One of the specimens was cast with a reference concrete mix with CEM I whereas in the other mix cement was partly replaced by fly ash. After casting, mineral wool was used to insulate the specimens in order to reproduce realistic conditions in large mass concrete elements. Temperature measurements enabled a direct comparison of the heat generated by each mix as well as the estimation of the strength development. Strain measurements, on the other hand, gave an indication of the variation of the degree of restraint along the height of the specimens. Using available models for concrete creep, the tensile stresses along the specimens were calculated at different heights and compared to the expected tensile strength in order to assess the crack risk. After removing the insulation, measured strains exhibited a strong dependence on external temperature variations. The test results proved useful to analyse the early-age behaviour of concrete.

Fibre-reinforced shotcrete (FRS) tunnel linings in hard rock are structurally intricate due to the complexity of rock mechanics and the interaction between shotcrete and rock. As the consequences of tunnel failure can be severe, maintaining the structural safety is vital in an operating tunnel. However, to satisfy safety demands, design- and maintenance measures can be conservative, as empirical methods and worst-case scenarios are commonly used in design and repair to account for the complexity of the system. A novel method for verification of tunnel linings, combining experiments, state-of-the-art distributed optical fibre sensing systems embedded in the shotcrete, advanced finite element modelling, and machine learning algorithms is in development. For the experiments, the characterisation of bond strength between rock and FRS are crucial to simulate trustworthy data.In this paper, a literature review and experiments are presented aiming to characterise a high and a low, non-zero, interfacial bond strength between two layers of concrete. The properties of the substrate surface in terms of roughness, microcracks, cleanliness and free water are investigated before casting. The experiments study four different surface treatments, including jackhammering, grinding, grinding and adding a layer of sand to the surface, and grinding and adding free water to the surface. The literature review showed hydrodemolition as a surface treatment method to have a consistently high bond strength, while the experiments showed a lower bond strength for ground surfaces than for jackhammered specimens. The inclusion of sand did not significantly decrease the bond strength, while the addition of water slightly increased the strength.

Real-time monitoring of structural health is a key issue for structural safety. Monitoring systems have evolved from external devices into intrinsic self-detection systems (SDS) becoming diagnostic and monitoring tools useful to maintain and increase structural durability. Furthermore, SDS are an economical and efficient solution for using human and technical resources towards sustainability. Self-sensing materials are considered a promising SDS technology to replace integrated connected or embedded systems, which have many limitations.Self-compacting concrete (SCC) is an advanced material that can become a self-sensing concrete by the incorporation of carbon-based materials, which provide the concrete matrix with piezoresistivity properties, transforming the material into a sensor by itself. The advantage of using SCC lies in its larger paste content which allows the use of hybrid systems of carbon-based additions, such as carbon nanofibres (CNF) and carbon fibres (CF). This combination can produce a synergistic response, improving the properties that can be achieved by incorporating each of them separately. Through the integration of electrical and piezoresistive properties, Piezoresistivity-SSC (PSCC) can collect real-time state variation information relating mechanical responses to piezoresistivity.The aim of this study was to identify the threshold of the effective admixtures content maintaining acceptable workability and achieving PSSC self-sensitivity.

Traditional methods for estimating structural deterioration are generally costly and inefficient, especially for non-accessible structural members. However, recent research has demonstrated that electro-mechanical impedance (EMI) or its inverse electro-mechanical admittance (EMA) measurements can be used to continuously monitor the structural integrity of reinforced concrete (RC) civil infrastructures in real-time. In this work, three lead piezoelectric zirconate titanate (PZT) transducers were epoxy-bonded on the external surface of a real-scale RC beam-column joint (BCJ) specimen. An integrated wireless impedance/admittance monitoring system (WiAMS) excites and simultaneously measures the voltage signal response of the PZT transducers in various imminent damage states. Furthermore, a scalar statistical index is employed to quantify the structural damage based on the variation of the PZT output voltage signals between their response at different damage levels and a pristine, undamaged state (initial healthy). The results of this study indicate that through the EMI technique, external epoxy-bonded PZT transducers can reliably evaluate the structural integrity of BCJs.

Recently, the usage of piezoelectric transducers for structural health monitoring (SHM) and damage diagnosis has received increasing attention. However, the effectiveness and accuracy of SHM methods are achieved to the greatest extent, not only by quantifying the level of the potential damage but also by the damage localization. In this work, a developed wireless impedance/admittance monitoring system (WiAMS) utilizes the frequency response measurements of an array of external epoxy-bonded small-sized lead piezoelectric zirconate titanate (PZT) patches to the surface of the tested specimens to identify and localize the flexural crack. The tested beams made of fiber reinforced concrete (FRC) were subjected to a four-point bending test under repeatable flexural loading (loading, unloading, reloading). Quantification and evaluation of the flexural damage were achieved using the frequency signal measurements of the PZT transducers installed in predefined locations of the specimen and statistical damage indices. Overall, the results indicated that the proposed methodology, using the proposed SHM system and an array of carefully placed PZT transducers, could effectively detect and localize potential flexural cracking of FRC structural members with high reliability.

EDF operates 56 nuclear reactors, 24 of which have a double wall structure as a concrete containment building. The inner wall is prestressed and has no metallic liner. Every ten years, an integrated leak rate test is carried out. The aim is to ensure that the leakage rate of the inner wall is below a threshold criterion. The forecast of the leakage rate during each test is an industrial challenge for EDF.To meet this challenge, a tool called the digital twin has been developed. This tool must be fed by material behaviour laws, which are themselves calibrated. To calibrate these models, two problems arise: on the one hand, the models are complex with a large number of parameters, and, on the other hand, the structures are not always thoroughly instrumented or the materials used sufficiently characterized. It is therefore necessary to find a strategy to calibrate the models as well as possible in order to have the most reliable predictions of both the long-term behaviour and the leakage rate. The proposed work attempts to develop a calibration methodology based on the VeRCoRs mock-up (1/3 scale mock-up of a double wall concrete containment building). Three calibration cases of varying richness are investigated: a reference approach with all the sensors available on the VeRCoRs structure, a degraded approach with the only data available on the operating reactors, and finally a hybrid approach with the data available on the operating reactors combined with information obtained from homogenization techniques (in particular, basic creep). These different approaches are compared to the reference case to conclude on the interest of the mixed approach.

In recent years, a main research focus has been set on the development of performance-based design concepts for the durability of concrete structures. These concepts are based on three general principles: (1) the use of validated material laws (models); (2) the adequate quantification of the material resistance and the environmental loads; and (3) a safety concept on a probabilistic basis. The latter sets a maximum allowed probability of occurrence of an undesired limit state. Therefore, we analysed numerous well-documented inspections of underground parking garages that underwent rehabilitation works. The focus was set on chloride-induced corrosion since it was the main reason for the rehabilitations. Due to limitations in the available information, we estimated the reliability index using approximate methods. We estimated the reliability index at which both the columns and the walls of the different projects were rehabilitated separately. We afterwards compared the estimated reliability indices to values recommended in the literature and to the used rehabilitation method. The estimated reliability index seems to agree with the recommendations for the target reliability index found in the literature. We did not find a significant difference between the reliability index values for which the two different rehabilitation methods were applied, suggesting that other factors should be considered.

Avoiding or limiting crack widths in massive concrete elements can be a challenging problem owing to the physical phenomena inherent to hardening processes occurring at early ages. In restrained elements, the increase of temperature at an early stage, due to the heat of hydration of cement, and the consequent cooldown at a stiffer stage, results in tensile stresses, which may lead to cracking or reduce the tensile capacity to sustain additional loading in the long-term. A recurrent set of questions, made by designers and scientists, is: do the concrete stresses due to hydration heat relax in the long-term? or do they need to be superposed to the stresses owing to long-term effects and applied loading? and, do the hydration heat effects influence the long-term crack widths? An extensive experimental campaign was recently conducted at TU Graz, to help answer these questions. But a different set of questions persists: how accurate are finite-element analysis methodologies (simulating the viscoelastic, time-dependent, concrete behaviour, cracking and bond-slip effects, at the macro-scale), to predict the developed concrete stresses and crack widths, since the early ages until the long term? The present papers intents to contribute to answering the latter, by performing the finite-element analysis of the beforementioned experimental campaign made at TU Graz, and by discussing the comparison between experiments and numerical analyses.

The blast furnace slag cement has been widely used for not only massive concrete but also general civil infrastructures in Japan from a viewpoint of by-product application and CO2 emission reduction. The thermal cracking and the dry shrinkage cracking issues, however, in the structures with the blast furnace slag cement have been reported in practice more frequently than those with ordinary Portland cement (OPC). It has been often explained that the cracking is likely to occur due to large autogenous shrinkage, small tensile creep and gradual strength development of concrete with the blast furnace slag cement but the dominant mechanism has not yet clearly found. The authors previously reported that drying shrinkage of concrete with the blast furnace slag cement B type was increased when high temperature is given at early ages while the high temperature could decrease drying shrinkage of concrete with OPC. It is plausible that the increase of drying shrinkage would be main cause to the cracking issues in the structures with the blast furnace slag cement, especially in the case of summer construction. In this paper, the effect of high temperature on drying shrinkage of mortar with the blast furnace slag cement is studied changing replacement ratio and temperature at early age to find the practical possibility to cause cracking in structures with the blast furnace slag cement. In addition, it was found that the effective addition of gypsum and limestone powder may inhibit the drying shrinkage of mortar with blast furnace slag cement even when the specimens are exposed to high temperature.

The scientific models for the calculation of the width of early age imposed strains cracks are based on various concepts and are constantly evolving. Due to the complexity of the matter considerable simplifying assumptions are employed. These include the member restraint factor (specified prior to its cracking) used not only for the determination of the risk of the primary crack formation, but also for the determination of subsequent cracks and the calculation of their width. Although such an assumption may lead to an approximation of the expected results, it is by no means compatible with the mechanical bases of member behavior after its primary cracking. In an attempt to address this problem, in the present paper the application of a new model for the calculation of the modification factor (Rσcr) for the degree of restraint before cracking, which takes account of the effect of various scales of cracking is proposed. The model enables a more accurate assessment of the risk of subsequent cracks formation together with the calculation of cracks width both immediately after their formation, i.e. taking account of the effect of member relaxation, and immediately prior to subsequent cracking. A parametric analysis was performed which indicated a significant impact of member geometry (i.e. cross-section and length of the member) on the change of the modification factor after cracking. Depending on the member geometry the limit values of imposed strains to the level of which reinforcement effectively restricts cracks width are also specified.

Nowadays Serviceability Limit State (SLS) of Reinforced Concrete (RC) structures is becoming a more and more important object of research among scientists and engineers. One of the most relevant topics of SLS is cracking due to its significant impact on the longevity and durability as well as aesthetic appearance of the structure. However, up until this day all theoretical models, dedicated to determining the most important characteristic of cracking behavior – crack width, are still highly debatable due to the high variation in the correspondence of the theoretical to experimental results. In this paper a new simple analytical approach for calculating average crack width of reinforced concrete members subjected to external short–term loading is presented. The new model is based on the concept of sole shear displacement occurring in the cover thickness of concrete due to the tangential stresses resulted by bonding. Theoretical crack width results obtained using the new approach are compared to the experimental results of tensile and bending members tested by different authors and the theoretical results of Eurocode 2 and Model Code 2010.

In times of climate change, responsible use of our natural resources is of great importance. For the optimization of concrete structures, the interdisciplinary cooperation of all parties involved is crucial already in the planning process. Through this cooperation, it is also possible to provide evidence of crack prevention as a result of hardening-induced restraint stressing, which enables significant savings in the minimum reinforcement for crack control. There are different existing verification formats, such as the cracking index, cracking probability or macrocrack index. The latter was developed primarily for the targeted assessment of the risk of macrocracks that cover the entire tensile zone, whereby only those restraint stresses that cause restraint forces are considered. The eigenstresses generated in the hydration process are not further assessed in the macrocrack index as they are assumed in engineering terms to reduce the risk of macrocracking. This paper questions this engineering assumption with special attention to the correct combination in time between restraint stresses due to restraint forces with the corresponding eigenstress profile using nonlinear thermomechanical FE investigations. The result of the research is a proposal for the consideration of eigenstresses for the assessment of the risk of cracking depending on the member type and thickness.

An accurate calculation of steel stresses is essential for assessing reinforced concrete structures’ serviceability limit state, e.g., assessing crack widths. The steel stresses in elements loaded in bending are not known but are estimated by steel stress calculations. To get a more accurate crack width prediction, the calculated steel stress should approximately represent the actual steel stress at the location of the crack after the crack has been formed. Existing methods for calculating steel stresses are frequently based on numerous assumptions; e.g., the tensile stresses or tension softening effects in the cross-section are neglected, and a linear stress-strain distribution is assumed for the concrete in compression. This paper presents a method to calculate steel stresses based on existing constitutive theoretical relations that consider concrete's non-linear behaviour in compression and tension. They are compared with strain measurements of the reinforcement bars using distributed optical fiber sensors obtained from experiments described in the literature. Results showed that existing methods frequently overestimated the steel stress, especially when the first cracks were formed. Therefore, a method was developed for an improved calculation of steel stresses in elements loaded in bending with a rectangular cross-section. The paper demonstrated that the developed method could estimate steel stresses more accurately from the first to the final crack. The presented method applies to rectangular cross-sections with a single reinforcement layer but can be straightforwardly extended to other shapes in a similar procedure and can be used to assess the accuracy of crack width formulations based on experimental results.

Cement-based materials are known for shrinkage strain on drying, causing easily crack initiation under internal or external restraint. Higher crack resistance can be achieved by slowing down the strength gain with slower chemical shrinkage evolution. The ring shrinkage test provides an accelerated method how to quantify cracking resistance on drying, supported with long-term experiments for concrete surface cracking. The experiments presented in this paper use ring shrinkage tests for 25 mortars, which cover 10 commercial cements and 15 on-demand cements, spanning Portland cements and blended cements for 30% slag substitution at maximum. The results proved that the ring cracking time increases while lowering the Blaine fineness or increasing slag substitution. A crack-resistant cements have upper limits for 2-day compressive strength and Blaine fineness which are for Portland cements as 27.7 MPa and 312 m2/kg, respectively. The results show that only two out of ten commercial cements can be considered as crack-resistant, while cements on-demand increase this ratio to 10 out of 15.

The article summarises the recent examples in distributed fibre optic sensing (DFOS) as a non-destructive approach for crack detection, especially during the hydration of early-age concrete. Thanks to the application of appropriate measurement technology (like Rayleigh scattering), the DFOS tool (e.g. monolithic and composite sensors with reduced axial stiffness), installation procedures (both for the surface and embedding inside the concrete) and finally, the post-processing algorithms, it is possible to detect all the (micro)cracks and estimate their widths. The qualitative and quantitative analysis based on DFOS strain measurements provides new possibilities for the structural assessment of concrete and reinforced concrete structures. Cracks formed during the thermal-shrinkage phase of the concrete structures in the first days of hardening are crucial for their later performance and final durability. Thus, knowing the actual crack state is of great practical importance. The paper provides guidelines for good practices in developing such measurements, including the design of the strain sensors being installed within the concrete. These considerations are supported by the example applications in the laboratory, including small-size concrete specimens and full-size reinforced concrete beams. Finally, the deployment within the real railway bridge was presented, and example results were discussed.

Consequences of climate change are becoming increasingly obvious and while resources are dwindling, buildings tend to be operated longer than originally expected and have to be maintained according to prolonged service life and more intense environmental impacts. Cracks and cavities are crucial for the durability of reinforced concrete structures and need to be filled, to ensure usability. Often, this is done with epoxy resins. While these polymers perform well under certain circumstances, they have many disadvantages such as heat-instability, high costs, high resource claim and hazards for environment and health. Thus, the Institute for Building Materials Research (IBAC) at RWTH Aachen University (Germany) is researching an eco-friendly and durable alternative binder based on geopolymers in collaboration with Diamant Polymer GmbH (Germany).This paper presents the latest results from the collaborative project and the development of a low-viscosity, high temperature stable geopolymer for crack injection and cavity filling. In several test rigs, experiments were carried out to investigate injectability, flow behaviour, mechanical properties, high temperature stability and the possibility to increase volume and induce preload. Through inorganic additives, the geopolymer expands or, if expansion is constrained, preloads itself during the hardening, which IS essential to create a durable backfilling as any volume reduction would create a new (smaller) cavity or crack. As further advantages, the high alkalinity of the geopolymer supports remaining the alkaline milieu in concrete and the geopolymer can be recycled similarly to concrete.

Since 2015, a new durable concrete design in a concept of multiple protection countermeasures has been applied to many bridges in Tohoku region of Japan to enhance the durability of RC deck slabs. Various studies pointed out that the utilization of expansive additive (EA) (dosage of 20 kg/m3) for ground granulated blast furnace slag concrete has been confirmed to be indispensable for reducing the early-age thermal tensile stress, which resulted in successful crack mitigation in highly durable RC slab of several steel girder bridges with one or two-span until the completion inspection. Nevertheless, in the newly constructed RC slab of bridges with three or more spans where stepwise construction stresses were added, noticeable transverse cracks were reported. In this study, tensile stresses produced by the stepwise construction of a four-pan steel box girder bridge were numerically investigated using a numerical simulation following layered model. Furthermore, the three leveled systematic thermal stress analysis for the durable RC deck slab of the bridge was also performed using FEM. According to the stepwise construction stress analysis, the authors proposed to increase the amount of EA from the standard dosage of 20 kg/m3 to 25 kg/m3 to further reduce thermal tensile stress in risky locations. Additionally, influential factors affecting the early-age thermal stress of the durable RC slab were numerically presented considering the application of the increased 25 kg/m3 EA. Finally, the cracking risk of the durable RC slab during 28 days of curing was discussed based on combined thermal and stepwise construction stresses.

Moisture transport in cracked concrete is one of the most important key phenomena which determines the deterioration of concrete structures by introducing undesired elements. Especially, the anomalous moisture transport of cement-based material, which does not follow the root-t law, should be explicitly understood. Since the calcium silicate hydrate, which is a major phase of cement-based materials and shows volume change as a function of water content, is the main reason for the anomalous moisture transport by changing the microstructure and macroscopic volume change of cement paste in concrete, these behaviors are explicitly and numerically taken into account in the moisture transport by using truss network model (TNM). This moisture transport model is coupled with a rigid-body spring network model (RBSM) which deals with cracks easily. The moisture transport in the cracked concrete was simulated and compared with the experiment and discuss the mechanisms of anomalous moisture transport.

In this paper, the effect of particles size and pre-saturation method of LightWeight Aggregates (LWA) on their water absorption coefficient are investigated (LWA are used to replace a part of the sand), as well as the effect of their particles size and content on the mechanical properties and autogenous shrinkage of mortars. To reach these objectives, two methods are performed to saturate LWA: normal and vacuum saturation. Additionally, two particles size ranges (0–2 mm and 0.63–1.25 mm) and three contents of LWA (0%, 10% and 15%) are also tested. Based on the results, the vacuum condition can effectively increase the water absorption of LWA by about 39%. The addition of finer LWA leads a better effect of autogenous shrinkage and mechanical properties and even slightly improves the mechanical properties of the mortar, thanks to its better spatial distribution.

The definitions of concrete crack widths of reinforced concrete slabs with seismic loads are often not clear and can only be determined to a limited extent with analytical models. Thus, an increasing number of investigations regarding practical crack width calculations and subsequent approaches with simulative and mechanical models are being researched and evaluated. Within this research project, the comparison and analysis of recognized theoretical models for crack width calculation will be carried out with a focus on earthquake-related design situations. Accordingly, a parametric calculation tool was established using the programming platform MATLAB. The tool enables a parametric calculation and investigation of the crack width due to flexural moments in concrete slabs. The Code of the calculation tool was written as a semi-automatic calculation routine in MATLAB. In this model, crack models of different design standards, are processed and the results are delivered in tabular and graphical form. The calculations and analyses are based on the normative crack models applicable in Europe and the USA, i.e. DIN EN 1992-1-1 (Eurocode 2) and ACI 224R-01R08. Additional boundary conditions related to seismic loading are accounted for as per ACI 318-19, DIN EN 1998-1, and ASTM A706 as necessary. To achieve higher reliability of the model, comparative calculations were carried out toward the verification of the tool based on previous similar research for beams and columns [1] and on a nonlinear finite element software specialized for concrete. Finally, the influence of various geometrical and material parameters has been also investigated based on parametric calculations.

The study is focused on the shrinkage behaviour of ultra-light foam concrete (FC) with embedded phase change material. Three basic strategies for reducing the shrinkage crack potential are investigated for FC with a density of 240 kg/m3. The microencapsulated Phase Change Material (PCM) was introduced to the foam concrete for thermal energy storage (TES) purposes. In the study, commercial Paraffin-based PCM with a melting/solidification temperature of 37 ℃ was used. The volume content of PCM in the paste applied in FC was 20%. The results confirmed the high level of shrinkage strains in the ultra-light PCM-embedded foam concrete and the high risk of early-age cracking, even in precast panels. Appropriate curing conditions have been found to be an effective way to produce ultra-light PCM precast panels.

Developing materials with enhanced thermal properties is fundamental to reduce the energy demand in buildings and consequently energy consumption. In this study, an experimental assessment of the use of textile fiber waste in cement-based composites for building applications was addressed. In particular, both mechanical and thermal characterizations were performed to evaluate the behavior of cement mortars incorporating two types of textile fibers in different percentages after 7 and 28 days of water curing, respectively. Results show that the addition of fibers has great potential to improve the thermal insulation capacity of buildings by reducing the thermal conductivity of cement mortar by up to 52%. Moreover, the textile fibers improved the mechanical strength of the cementitious mortar, especially with a high percentage of textile and a prolonged period of curing.

Thermoelectric energy is one of the promising renewable energy technologies. Research has been focused on finding new materials that have higher efficiency. While most research focuses on electronic thermoelectric materials based on solid materials, recent research also started to head towards ionic thermoelectricity utilizing the ionic conductivity of liquids and gels. Recently, more materials with p-types thermoelectric properties have been developed than n-type. More n-type thermoelectric materials are needed to be developed to produce more energy from thermoelectric modules. This paper aims to (1) illustrate the concept of combining electronic and ionic thermoelectric material properties, (2) develop an n-type thermoelectric generator using MnO2 nanopowders and cement paste which acts as a core of the sample, (3) present a novel way to compensate the strength loss through casting high strength concrete shell around the thermoelectric core. Finally, a parametric study is carried out to investigate the role of KOH, MnO2, inner core size, and the effect of temperature gradient on ionic conductivity.

Climate change and global warming are problems that our planet is currently leading with. Main outcomes of Climate Change Conferences all around the globe, like the COP27, deal with the reduction of CO2, the removal of inefficient fossil subsidies and the promotion of renewable energies. To achieve these goals, this work presents new cementitious materials to be used as thermal energy storage in concentrated solar power technologies. These new materials (alkaline cements and hybrids cements) avoid the use of Portland Cement (PC), whose manufacturing emits between 7% and 9% of the global CO2 emissions. These eco-efficient materials, after the exposure to high temperatures, present better mechanical properties than the ordinary mortar composed of PC, and in addition, they could offer improvements of the thermal properties (i.e., either the thermal conductivity or the specific heat). After presenting the experimental tests and data, a finite-element-based approach is implemented for simulation purposes. A parametric study is carried out to find the optimum heat exchanger configurations that maximize the thermal energy storage. In order to define the best composition of the block (i.e., material, distribution of the tubes), the systems are compared by taking into account a storage of 1100 MWh given in a parabolic trough power plant of the ANDASOL-type.

A metamaterial is a composite with unprecedented properties, either in nature or in the market. Specifically designed, a metamaterial exhibits either extraordinary or “à la carte” macroscopic physical properties, or allows the device made of it (the “metadevice”) to have an optimal response. In the context of the thermal performance of a building, let the metadevice be the whole building envelope, say the “metaenvelope”. Then, the metamaterial in the metaenvelope is determined in order to maximize the building energy efficiency. To this end, we apply the optimization-based metamaterial design approach, which consists in solving a nonlinear constrained optimization problem where the objective function is the energy consumption for cooling and heating, and the design variables define the metamaterial in the envelope. Particular emphasis is given to the use of NRG-foams, which are foamed concretes with embedded microencapsulated phase change materials developed within the framework of the EU H2020 project NRG-STORAGE. Finally, metaenvelopes having NRG-foams as insulation materials will be compared with a standard envelope in terms of the energy consumed by the enclosed building to keep the indoor thermal comfort.

In the last years, the sensitivity towards environmental impacts of industrial activities is of growing interest. Construction sector, with particular reference to cement-based materials, possesses a high environmental footprint due to raw resources’ consumption and waste, energy use, greenhouse gasses emissions produced during the preparation of the construction materials and the building and service life of structures. A possible solution to decrease the impact of cementitious building materials is to develop novel multifunctional eco-friendlier binders for enhancing the thermal properties and sustainability of the material. The composite investigated in this paper is an earth cement composite doped with carbon microfibers, named “smart-earth concrete”. The material’s binder is composed by both cement and clay, in the proportion of 2/7 in volume. The carbon micro-fillers are added in order to enhance the sensitivity of the composite and provide multifunctional properties, such as sensitivity to mechanical strain and changes in physical conditions. The thermal and sensing capabilities of the smart-earth concrete are investigated through dynamic environmental tests and electrical acquisitions carried out on samples in thermal chamber under controlled changes in temperature and humidity. The innovative earth-cement composite demonstrated good thermal energy storage potential. Moreover, the electrical monitoring of the smart material allowed to properly identify temperature and humidity environmental fluctuations. The proposed composite appears promising for application in real-scale constructions, enhancing the energy efficiency of the structures and providing sensing capability for their monitoring during their service life.

The inclusion of Phase Change Materials (PCMs) in buildings has attracted large interest worldwide due to their ability to reduce energy consumption by stabilizing thermal excursions. PCMs have a high heat of fusion, which makes them capable of storing and releasing large amounts of heat during a phase transition. This paper presents an innovative concrete tile, produced by incorporating a microencapsulated PCM with phase transition temperatures between 23 and 26 ºC. Firstly, recent applications of PCM in concrete are discussed. Then, the design mix and several experiments about the incorporation of the new PCM-enhanced concrete are presented. After having described the process of tile design, thermal and mechanical tests are reported. The new concrete tile was hence used in a zero-energy house built for a Solar Decathlon. The use of the PCM-concrete floor tiles confirmed the reduction in energy consumption during the cooling period, and the increase in indoor thermal comfort. The inclusion of the PCM in this high performance building demonstrates the advantages of latent heat thermal energy storage in lightweight buildings. The challenge of controlling sun energy penetration, PCM cycles of charging and discharging, and the passive heat exchanges with the PCM tiles are discussed. Finally, some modelling results are presented to assess the impact of climate.

In this work, a commercial phase change material (PCM) was stabilized in biochar, by vacuum impregnation technique and later incorporated into cement pastes to be used in real building applications. The selected paraffin is characterized by a phase transition temperature of 27 ℃, i.e., within the most common thermal comfort conditions in building applications. The obtained compounds were analyzed at various scales of investigation using advanced thermo-chemical techniques, to properly assess the composites’ thermophysical performance and long-term stability. The obtained results highlight the promising thermal buffer capability of the shape-stabilized samples during the early-stage hydration process. In general, all the compounds tend to lose PCM during cycling, but significant leakage was only found after 1000 thermal cycles, suggesting a relatively stable behavior. Adding the shape stabilized PCM lowers the peak temperature by about 4 and 5 ℃ compared to the normal and the biochar-doped composite with positive consequences regarding compressive strength.

Effective and efficient recovery, storage, and reuse of heat, together with renewable energy, play an indispensable role in decarbonising the built environment. Thermochemical energy storage materials possess the highest volumetric energy density compared to latent and sensible heat storage materials under similar conditions. However, conventional thermochemical energy storage materials face several challenges including high cost, low sustainability, and limited heating power. Alkali-activated metakaolin (geopolymer) containing alkali aluminosilicate hydrates (N-A-S-H) has been shown to have a considerable thermochemical heat storage capacity at medium temperatures (below 400 ℃) but is less efficient at low-temperatures (<200 ℃). Here we investigated a salt impregnation method to form geopolymer composites for improving their thermochemical heat storage capacity at low charging temperature. More specifically, the effect of CaCl2-impregnation on the composition of the composites was examined with X-Ray Diffractometry and Fourier transform infrared (FTIR) spectroscopy. The dehydration enthalpy and volumetric energy density of the composites were assessed with differential scanning calorimetry (DSC), while dynamic water sorption (DVS) was used to study their water cyclic water sorption capacity. It was shown that short-time salt-impregnation can improve the heat storage capacity of the geopolymers, while a prolonged exposure to the salt solution can have adverse effects.

The need to reduce the energy for heating and cooling is leading to a renewal of interest in geo-sourced materials for modern building construction. These materials offer many advantages in terms of climate change adaptation, and reduction of CO2 emissions from building materials. This study presents the characterization of clay, fiber, and hygrothermal characterization of two types of clay mixtures reinforced with natural vegetable fiber for use in modern construction. Cob is a mixture of clay, water, and vegetable fibers. It is non-load bearing and serves as a filler for the wood frame. The wall design is suited for lightly seismic zones. Cob has great potential for applications in places with high housing and cooling needs. The hygrothermal properties of 30 clay formulations containing 0%, 3%, and 6 wt% wheat fibers were evaluated. At this fiber content, the material is considered a heavy type of cob. The measured thermal and hydric properties of the clay-fiber mixture presented in this paper are thermal conductivity, thermal effusivity and diffusivity, specific heat, water absorption, water vapor permeability, moisture buffer value (MBV), and sorption/desorption isotherms. Wheat fibers used in clay material mixtures improve their hygrothermal properties for sustainable construction. These results allow the development of a model hygrothermal model of wall elements.

The improvement of energy efficiency in buildings is the goal of many new European standards and regulations. New building technologies and materials are being designed to achieve this goal by integrating new properties through new dynamic environment responsive and recycled components. In this study, lime cement pastes with phase change materials (PCM), due to their thermal storage capacity, and biomass ashes, because of their good mechanical and physical behavior, were investigated.An experimental program was carried out to assess the synergies and effects of the biomass ashes and PCM on the mineralogical, physical, mechanical and thermal performance of the mixtures. Nine cement-lime pastes were designed, where 10 and 20% cement was replaced by biomass ashes and 10% and 20% of microencapsulated paraffin waxes PCM were incorporated. Bulk density, open porosity, capillary water absorption, compressive and flexural strength, Ultrasonic Young Modulus and thermal conductivity were characterized.It was found that biomass ashes did not modify significantly the mixtures properties while increased material’s sustainability. On the hand, PCM changed the physical, mechanical, and thermal properties of the mixtures that can be advantageous for building applications as mortar renders. The larger the PCM addition, the higher the mixtures properties changes.

Energy demand for heating and cooling represents a large part of building´s (residential and non-residential) energy consumption around the world. Development of thermal insulating construction elements with thermal energy storage and release capacity could be one way of reducing this consumption while maintaining thermal comfort inside the buildings. Using phase change materials (PCMs) as thermal storage/release materials for “porous” cement-based construction elements is a possible solution. However, the relatively low thermal conductivity of the cement matrix could impair the efficient transfer of the heat to the PCM reducing its effectivity. Addition of thermal and electrically conductive nanoparticles such as graphene-based particles could improve enough the thermal and electrical conductivity but maintain a good energy storage capacity. In this study the production of cement pastes with different dosage of PCMs (20% and 40% in volume) and reduced graphene oxide will be described. Furthermore, the characterization of their thermal and electrical conductivity, latent heat and thermal diffusivity will also be shown and discussed.

The RILEM TC 275-HDB - Hygrothermal behaviour and Durability of Bio-based materials aimed to investigate testing methods of hygrothermal and capillary behaviour on vegetal concrete. Usual protocols were considered in Round Robin Tests (RRT) to assess their applicability and to point out warning aspects. The studies were performed on hemp concrete provided by an industrial partner of the TC (VICAT Group), with density about 330 kg/m3. Regarding the measurement of Moisture Buffer Value (MBV), seven laboratories took part to the study. As the participating laboratories commonly used the NORDTEST protocol to measure MBV, this RRT was performed “as usual”, without additional guideline except initial conditioning of specimens. The results differ more or less between laboratories. Their analysis allows identifying several shortcoming regarding the exchange surface, the moisture flux direction versus the compacting one and the climate chamber technology. A second RRT has to be performed to formulate a more detailed protocol suitable for vegetable concrete and to assess its robustness.

This article presents an investigation on the rheological behavior of 3D printable bio-concretes containing rice husk fine particles. This agro-industrial waste was used to adjust the fresh-state properties of the concrete mixture, required for the printing process, while decreasing its environmental impact. In this study, the rice husk content varied from 5 to 12.5%, in mass of solids. The rice husk was submitted to a crushing process and two different particle sizes were investigated. The static yield stress was measured using a rotational viscosimeter equipped with a Vane spindle after different resting times. The results were used to obtain the thixotropic build-up rate and to calculate the printing parameters, such as layer height, time between successive layers and printing velocity. The results showed that the use of rice husk increases both the initial yield stress and the thixotropic build-up rate of the bio-concretes, which leads to an increase of the maximum layer height and the maximum printing velocity. Finally, the results showed the feasibility of using biomass for improving the buildability and printability of the mixtures.

The present study was designed to investigate the bond mechanism between flax nonwoven fabric reinforced lime mortars and four different types of masonry stones. The researchers carried out a comprehensive characterization of the mortars and stones, and analyzed the interface between these materials based on bond extension and flexural strength. The results showed that bond strength values were directly related to adherence extension, which was dependent on surface treatment (such as water, lime, and latex). The flexural tests conducted on stones strengthened with the flax nonwoven fabric reinforced lime composite revealed that the latex treatment showed the best performance. This study provides preliminary evidence that the use of flax nonwoven fabric reinforced lime composite may be an effective method for masonry strengthening. However, further research is necessary to reach a comprehensive conclusion. Further studies may include an investigation of the effects of different types of latex, the influence of curing conditions on bond strength, and the long-term performance of the strengthening system. The results of this research may have important implications for the conservation and strengthening of historic masonry structures, as well as for the design of new masonry constructions.

Hemp concrete is a promising product that has a wide range of properties and diversification. It is a sustainable material, with good thermal and acoustic properties. Being plant-based material, it has also the ability to absorb carbon dioxide, leading to significant reduction in carbon footprint. This paper investigates the role of hemp aggregate by characterising the hemp aggregate and testing the compressive strength of hemp concrete. The characterisation of hemp aggregate included testing its grading, water absorption and bulk density. Factors that affect the mechanical behaviour of hemp concrete were investigated, including water to lime (W/L) ratio, binder to hemp (B/H) ratio, pre-saturation of hemp and degree of compaction. Statistical models were derived to determine the significance of each factor and their interactions. Characterisation of hemp revealed that majority of hemp shiv retained between 1.18 to 3.35 mm sieve. The water absorption of hemp was approximately 300% after 48 h and bulk density was around 95.4 kg/m3. Models suggest that W/L and B/H were the most significant parameters affecting the compressive strength of hemp concrete.

Hemp concrete is an ecological bio-based building construction material, with several environmental benefits. It is made up of a lime matrix with hemp fiber inclusions, which makes it very heterogeneous and hygroscopic. Hemp concrete has a relatively low density which results in a poor thermal conductivity and good thermal insulation.The aim of this paper is to study the morphological and thermal behavior of hemp concrete when subjected to normal and severe temperatures, such as in the case of fire, or aging studies.Various non-destructive imaging techniques were used, to optimize the morphological and thermal characterization of hemp concrete, using specialized and innovative processing approaches.First, thermal solicitations were applied to hemp concrete using thermal tomography, which involves applying thermal stress while performing the scans (in-situ). To produce heat flow, an original tomographic plate is employed, and temperatures ranged from −20 ℃ to 160 ℃. The resulting 3D reconstructions of the real volumes of materials were investigated using Digital Volume Correlation to quantify the resulting deformation for the different studied thermal levels.After that, a Keyence optical microscope was used to track the interface morphological changes when high temperatures reaching 600 ℃ were applied.The obtained results showed an accentuated anisotropic behavior of hemp concrete when subjected to high temperatures. Big differences in the hemp fibers and cement matrix were identified when analyzing the three-dimensional strain fields. In addition, a particular attention was devoted to the study of the interfaces between the hemp fibers and the cement matrix.

Integrate bio-resources in construction materials is a key to reduce the environmental impact of the building industry. The hemp, as local and annually renewable plant resource, proves to be particularly suitable.The study presented in this article is a part of the “INNOFIB” ADEME project. The objective of this project is to develop an innovative industrial process of functionalisation of hemp fibre by dry process. The resulting product will be usable as thermal insulation material. The thermal properties of such material applied by blowing appear to be directly linked to the bulk density. One challenge of this project is to identify the hemp fibre morphology that leads to the best thermal performances. Several refined fibres shaped using various industrial processes, and reference insulating materials, are subjected to characterisation tests. Laboratory protocols, adapted to be applied to fibrous materials, evaluate the morphology, physical and thermal properties of bulk fibres: shape, length average fibre diameter, density, and thermal conductivity. Interestingly, for such bulk fibre materials, the thermal conductivity appears as a decreasing function of the density for the lowest densities. The thermal conductivity calculated with a predictive model including conduction and radiation is compared to the experimental data. The obtained results guide the selection of the best industrial process for the fibre preparation. The selected solution is then applied in the attic of a house used as demonstrator. Temperature and heat flux sensors are placed to record the data in real conditions. The on-site measurements are used to check the compliance of the effective thermal performances.