Proceedings of the RILEM Spring Convention and Conference 2024

Inhaltsverzeichnis

1. Frontmatter

2. TRC

   1. Frontmatter

   2. Investigation of the Bond Behaviour Between Geopolymer TRM and Concrete

      Ioanna Skyrianou, Christos G. Papakonstantinou, Lampros N. Koutas

      Abstract

      Aiming towards sustainability in the construction sector, various alternatives to cement-based materials have been proposed, with geopolymers being an excellent candidate due to their reduced carbon footprint as well as their exceptional mechanical and durability properties. With an increase in the need for external strengthening of structures, the use of textile-reinforced mortars (TRM) has been in the spotlight lately. This study aims to investigate such a strengthening system which uses alternative materials to cement-based matrices. The study focuses on the bond behaviour between textile-reinforced mortar using a binary geopolymer mortar as a matrix and a concrete substrate. A conventional TRM system employing a cement-based matrix was also investigated and used as a reference. The investigative parameters include the type of matrix (geopolymer or cement-based) and the bond length (50, 75, 100, 150 mm). For this purpose, a total of 8 twin specimens were prepared and tested by modified beam test. The results showed that specimens employing the geopolymer mortar achieved higher peak load than their cement-based counterparts regardless of the bond length by 25–94%, while also achieving higher vertical displacement by at least 14%. When geopolymer matrix was used the effective bond length was lower than the cement-based TRM although both systems exhibited the same failure mode.

   3. Enhancing Textile-Reinforced Concrete Sustainability and Economic Efficiency with Innovative Cement Composites

      Mohammad Alma’aitah, Bahman Ghiassi, Fragkoulis Kanavaris, Michael Sataya

      Abstract

      Significant attention has been garnered to Textile Reinforced Concrete (TRC), a novel composite material comprising a cement-based matrix with high-performance textiles, due to its exceptional mechanical and durability properties. In response to environmental and economic challenges in constructions, this study focuses on enhancing the sustainability and economic efficiency of TRCs through development of innovative low carbon, low-cost concrete matrices utilizing composite cements. Ternary and quaternary blended cement mixes, incorporating Portland cement, ground granulated blast furnace slag, limestone, and/or silica fume, with 65% to 70% cement replacement levels, were developed. The concrete mixes developed in this study achieved optimal workability and compressive strength, resulting not only significantly reduced costs but also lower equivalent CO₂ emissions compared to TRC mixes of an equivalent strength class documented in the existing literature. Furthermore, the investigation explored the flexural performance of TRC composites, incorporating the developed concrete mixes and Alkali resistant-glass textile, revealing valuable insights into the material's response to bending forces.

   4. Reinforcing Potential of Mineral-Impregnated PBO Fibre Yarns in a Sustainable Blended Matrix

      Cesare Signorini, Marco Liebscher, Viktor Mechtcherine

      Abstract

      Textile Reinforced Concrete (TRC) is now a key technology for the structural rehabilitation of deteriorated concrete structures, as well as for novel, versatile and highly customisable thin structures with optimised raw material utilisation. In order to fully exploit the excellent strength and modulus of high-performance fibres, like PBO, a uniform impregnation of the yarns is generally applied to achieve optimum stress transfer from the inorganic matrix to the load-bearing reinforcements. Mineral impregnation techniques for high-tenacity multifilament textiles are gaining increasing popularity over their polymeric counterparts mainly due to their enhanced thermal stability and good potential for reducing environmental impact. This paper presents and discusses the pull-out behaviour of PBO yarns embedded in a newly developed limestone calcined clay cement (LC³) mortar. Emphasis is placed on the bond properties of two grades of PBO fibres through pull-out tests. It is shown that the mineral impregnation plays a crucial role, not only in improving the mechanical response in terms of bond, but also in overcoming the differences in stiffness and properties of the PBO fibres, allowing the use lower grade fibres without compromising the overall performance of the composite.

   5. Influence of Carbonation Curing Conditions on Fiber-Matrix Interfacial Properties in Cementitious Composites

      Gu Lei, Dhanendra Kumar, En-Hua Yang

      Abstract

      The mechanical properties of cementitious composites subjected to carbonation curing depend on the carbonation degree, which is influenced by the diffusion of CO₂ within the cementitious matrix. It has been found that due to the decrease in CO₂ diffusivity as the curing progresses, the carbonation hardening is not uniform across the cross-section of the composite. The non-uniform carbonation of the cementitious matrix is expected to significantly influence the fiber-matrix interaction in fiber-reinforced composites (FRCs) subjected to carbonation curing. This study aims to understand the effects of carbonation curing regimes on the fiber-matrix interfacial properties. Single fiber pullout tests using polyvinyl alcohol (PVA) fibers embedded in reactive magnesia cement (MgO) matrix were conducted to determine the chemical bond, frictional bond, and slip hardening parameters. Three different curing conditions – 10% CO₂, 0.5% CO₂, and ambient curing (i.e., 0% CO₂) were investigated. Results showed that the chemical bond between the fiber and matrix is higher when subjected to carbonation than ambient curing for oil-coated fiber, whereas non-coated fiber showed reduction in chemical bond when subjected to carbonation. The fiber-matrix frictional bond increased with the increase in CO₂ concentration. The effect of CO₂ concentration on slip hardening was negligible. These experimental results will aid in modifying the fiber-bridging analytical models to account for the non-uniform carbonate hardening of the cementitious matrix in FRCs.

   6. Tensile Response and Durability of Flax-TRMs

      Mattia Baldassari, Niki Trochoutsou, Alessia Monaco, Pietro Cornetti, Maurizio Guadagnini

      Abstract

      Textile Reinforced Mortar (TRM) systems are currently among the most effective retrofitting solutions for masonry structures, thanks to their high compatibility with the substrate, and reversibility. Recently, the adoption of natural textiles as reinforcement in TRM systems has attracted the interest of researchers and industry, due to their great potential of providing a cost effective and sustainable solution while ensuring adequate structural performance. Despite the increasing number of studies focusing on the characterisation of short-term tensile properties, the long-term durability performance of natural TRMs, which is fundamental to ensure their viability in construction applications, has not been examined in detail. This paper aims to investigate the tensile behaviour of flax textiles and flax-TRM composites and assess their residual performance after exposure to accelerated ageing. Composites consisting of two and three layers of a bi-directional flax fabric embedded in a lime-based mortar were conditioned in water for 1000 h and 2000 h at controlled temperatures of 23 ℃ and 40 ℃. Bare textiles were also aged in an alkaline solution for equivalent exposure times and temperatures, to replicate the conditions within the lime-based matrix environment. Both unconditioned and aged textiles and composites were tested under uniaxial tension to determine their tensile behaviour. The complete load-deformation response was assessed employing both contact and non-contact methods (i.e. 2D Digital Image Correlation). It is shown that ageing strongly affects the textile reinforcement, resulting in a significant strength loss of the composite system.

   7. TRC Application Potential to Strengthen and Repair Concrete Structures Exposed to Fire

      Klajdi Toska, Anne-Lise Beaucour, Flora Faleschini, Carlo Pellegrino, Albert Noumowe

      Abstract

      Exposure to high temperatures, during fire events, can significantly affect the structural safety of existing buildings or infrastructures. Evaluating the effectiveness of retrofitting interventions or the repairability of damaged structures after fire is of fundamental importance to guarantee adequate structural reliability levels. The paper deals with the application potential of textile reinforced composites (TRC) (i.e. Textile reinforced mortar (TRM, Fabric Reinforced cementitious matrix (FRCM), etc.) both in retrofitting and repair techniques for heat damaged concrete elements. Some experimental tests, carried out on standard small scale concrete specimens, exposed to different temperature levels, are presented. The results show that: 1) thermal stress can significantly influences the behaviour of concrete retrofitted through TRC and 2) repair interventions through TRC were able to fully or partially restore the initial strength of the heat damaged material. Averall, textile reinforced composites showed a high potential to be applied in retrofitting and repair interventions of concrete elements damaged due to high temperature exposure.

   8. High Temperature Performance of Lightweight Concrete-Textile Reinforced Cementious Composite Sandwich Panels: A Comprehensive Investigation

      Matthieu Pettmann, Tine Tysmans, Dimitrios G. Aggelis, Anne-lise Beaucour, Javad Eslami, Albert Noumowe

      Abstract

      This research presents preliminary results of the development of a lightweight, sustainable and fire-safe structural insulating panel by combining very lightweight aggregate concrete (VLWC) as a core and textile-reinforced cementitious composite (TRC) as skins. The potential disadvantage of this system using TRC compared to steel reinforced concrete may be its behaviour under fire. A VLWC, with expanded clay aggregates, was developed focusing on density and high temperature stability. This study investigates the behaviour of each of the constituent materials, TRC and VLWC and then of their combination in the sandwich structure at ambient temperature and cooled-down after being submitted to elevated temperature. The residual mechanical behavior of VLWC after heating up to 600 ℃ has proven to be as satisfactory as traditional concrete, if not better, particularly regarding tensile strength. The effect of high temperatures up to 600 ℃ on the tensile behaviour of TRC with coated-AR glass fibers was investigated. The first cracking stress and the ultimate tensile strength decrease with the temperature from 150 ℃. But the originally three-staged response (in ambient conditions) is maintained up to 300 ℃, and the ultimate strength is still significantly improved compared to the first cracking stress value. For the sandwich panels, no delamination from the skins appears. At ambient temperature, a similar three-stage behaviour is observed with satisfactory mechanical behaviour. Up to 300 ℃, the residual behaviour is similar, with a limited decrease in maximum loading. Yet, at this temperature, a few specimens undergone delamination during the heating phase.

   9. Effect of Panel Thickness on the Uniaxial Tensile Behaviour of Glass Textile Reinforced Concrete

      Ramakrishna Samanthula, Ravindra Gettu

      Abstract

      Generally, it is known that the tensile strength of plain concrete decreases with the size of the element, which is attributed to the higher probability of having larger and more microstructural defects in larger elements or the effect of the propagation of the fracture process zone. There is limited information on the size and scale effects on the strength of strain-hardening cement based composites such as Textile Reinforced Concrete (TRC), which are beneficial for developing structural sections that are allowed to crack in a stable manner before failure. The size effect on tensile response of TRC is necessary for rational design and implementation of large-scale applications. In the current study, composite panels of different thickness (i.e., 10, 20, 40 mm) were fabricated using a cementitious matrix and coated E-glass textiles reinforcement; four layers of textile were used in all the panels. The specimens were monotonically loaded under direct tension in accordance with RILEM TC232. The specimens have shown a slight reduction in the first crack stress with increasing thickness, as can be explained based on statistical scale effects. Also, the overall tensile response transitions from strain-hardening to strain softening behaviour as specimen thickness increases. More interestingly, the number of cracks decreased with increasing size at any given strain. Further, DIC analyses reveal that the crack pattern and crack widths are significantly affected by the panel thickness.

3. Self Healing

   1. Frontmatter

   2. A Data-Driven Model to Predict the Self-healing Performance of Ultra High-Performance Concrete

      Bin Xi, Aayush Upadhyay, Radakrishna G. Pillai, Liberato Ferrara

      Abstract

      Ultra High-Performance Concrete (UHPC) demonstrates superior mechanical properties and durability compared to ordinary concrete. The self-healing ability of UHPC has also been widely observed in numerous studies. Consequently, the development of a predictive model capable of forecasting the evolution of UHPC's self-healing performance under diverse exposure conditions has become crucial in order to reliably and effectively exploit this potential in the framework of a durability-based design of UHPC structural applications. In this study, an extensive dataset was collected and established through experimental tests focusing on the crack-sealing performance of UHPC. These tests simulated the conditions in which pre-cracked UHPC specimens were subjected to sustained tensile stress, while simultaneously exposed to exposure environments, including fresh water, salt water and geothermal water. Based on this dataset, a mathematical regression model was constructed, incorporating significant factors such as crack width, exposure environment, and exposure time for UHPC. The results demonstrate the remarkable accuracy of the proposed mathematical model in predicting the self-healing ability of UHPC.

   3. Self-healing Performance of Recycled UHPC Under Chloride Exposure

      Marco Davolio, Estefania Cuenca, Ruben Paul Borg, Liberato Ferrara

      Abstract

      Strategic structures can benefit from the characteristics of Ultra High-Performance Concretes (UHPC) to achieve long term durability without substantial maintenance. However, in some cases the aforesaid structures may still need to be dismantled. Thus, the possibility to recycle UHPC can significantly affect the environmental impacts associated with the use of this category of materials, given the high binder content and embodied energy. This study has investigated the self-healing performance of a UHPC made with recycled UHPC. Two different mixes were studied, with total replacement of sand and partial replacement of cement by recycled UHPC aggregates and recycled UHPC aggregates and fines respectively. The self-healing capacity of the mixes was addressed with mechanical and durability tests up to six months, with continuous exposure to a chloride-rich solution, simulating the marine environment. The unhydrated cement particles preserved the self-healing capacity of the parent UHPC. Both mixes proved their crack-sealing potential even with repeated damage-healing cycles, exhibiting a slight decrease only after six months of exposure and cracking. The crack closure resulted in a constant mechanical performance which was maintained over time.

   4. Modelling the Effects of Crystalline-Stimulated Self-healing on Chloride Transportation into Cracked Concrete

      Zhewen Huang, Estefania Cuenca, Liberato Ferrara

      Abstract

      The ingress of chloride ions in concrete induces the corrosion of reinforcement, leading to a degradation of the mechanical performance of the intended structural applications. The incorporation of crystallizing admixtures imparts autogenous healing to conventional concrete, enabling cracks to seal by themselves and thereby reducing the infiltration of chloride ions. Recognizing the inherent heterogeneity of plain concrete, this study formulates a mesoscopic numerical model in the framework of finite element method. The model conceptualizes concrete as a three component structure: coarse aggregate, mortar matrix, and interfacial transition zones (ITZs). To account for the influence of the self-healing phenomenon in concrete, two further phases representing cracks and damage zones (DZs) are introduced. The coarse aggregate phase is considered impermeable, with chloride ion diffusion assumed to occur in the remaining four phases. The self-healing process of cracks was simulated by using the moving mesh technique in COMSOL, with reference to the method of establishing the kinetic law of crack self-healing in the follow-up of Horizon 2020 ReSHEALience project, undertaken in the project MUSA, funded through the Italian National Resilience and Recover plan. Validated against experimental data, the model not only reproduces the crack closure process but also offers predictions on chloride transport. This simulation model contributes to the exploration of concrete resistance to chloride permeability, elucidates the transport mechanism of chloride ions within self-healing concrete, and provides insights for designing durable concrete structures to mitigate the corrosion of steel reinforcement or steel fibers.

   5. Self-healing Mechanism and Crack-Filling Performance of Multi-functional Bacterial-Laden Fiber (Biofiber) in Cementitious Matrix

      Mohammad Houshmand, Seyed Ali Rahmaninezhad, Caroline L. Schauer, Christopher M. Sales, Ahmad Najafi, Yaghoob (Amir) Farnam

      Abstract

      Recently, we developed multifunctional bacterial-laden polymeric fibers (BioFibers) as an innovative delivery system to introduce a bio-self-healing capability into quasi-brittle composites. These BioFibers consist of a load-bearing core-fiber, a bio-compatible hydrogel sheath, and an outer protective damage-responsive shell layer, engineered to endow the matrix with three key functionalities: (i) bio-self-healing, (ii) control over crack growth, and (iii) damage-induced self-activation. This study focuses on evaluating BioFibers’ efficacy in filling cracks within a cementitious matrix. BioFiber-reinforced cement paste samples (BioFRC) were prepared, cracked under controlled flexural conditions, exposed to wet/dry cycles with bio-agent solutions, and monitored for the development of crack-filling efficiency over time. BioFRC specimens were prepared with a BioFiber reinforced zone. Controlled loading was applied to the specimens to induce cracks with the widths of 100–150 μm. Following crack initiation, samples underwent wet/dry cycles: 1 h submerged in a bio-agent solution (urea, yeast extract, and calcium acetate at 20 g/L each), followed by 23 h of dry conditions at 23 ± 1 ℃ for 28 days. Crack-healing efficiency was assessed at 0, 14, and 28-day intervals post-exposure. Moreover, self-healing end-product precipitations were collected from sacrificial samples for material characterization, including thermogravimetric analysis and scanning electron microscopy. Results indicated that precipitations from activated BioFibers achieved a crack-filling ratio of 93.7 ± 3.3% for cracks with an average width of 129 μm after 28 days of exposure. Material characterization tests revealed the formation of calcium carbonate crystals, including combinations of calcite and vaterite, in the healed samples.

   6. Methodology for Assessing the Enhanced Flexural Fatigue Life of Ultra High-Performance Concrete Due to Self-healing

      Niranjan Prabhu Kannikachalam, Nele De Belie, Liberato Ferrara

      Abstract

      This paper provides an overview of techniques for evaluating flexural fatigue life, delving into their applicability to ultra high-performance concrete (UHPC). The consensus on the impact of fibre inclusion on fatigue life of fibre-reinforced concrete (FRC) remains elusive. The intricate interplay of varied fibre parameters, loading frequency, and matrix composition complicates the understanding of FRC behaviour under cyclical loads. The absence of standardized test procedures hampers the correlation and extension of published results. Despite these challenges, a positive impact on fatigue performance under flexural loading is revealed, suggesting that fibres, under tensile forces, bridge cracks and extend fatigue life. This paper proposes a methodology to assess self-healing induced enhancement of the flexural fatigue life of UHPC in high-cycle fatigue loading, focusing on stiffness and the rate of crack opening displacement. Initially, specimens underwent 700,000 cycles as a fatigue pre-healing condition. Following the healing process, the specimens were subsequently subjected to up to 2 million cycles at a frequency of 5.5 Hz. UHPC specimens demonstrated up to 10% improvement in stiffness and a reduction of up to one order of magnitude in the rate of crack opening displacement with three months of healing in submerged condition.

   7. An Lca Perspective on Membrane Emulsification for Microcapsules to Be Incorporated into Self-healing Concrete

      Davide di Summa, Claire Riordan, Dave Palmer, Abir Al-Tabbaa, Liberato Ferrara, Nele De Belie

      Abstract

      Cement-based materials, vital in construction for their properties, face challenges due to crack formation compromising structural integrity. Thus, self-healing materials have been demonstrated to be crucial in extending structure lifespan and enhancing overall sustainability. More specifically, capsule-based healing, with the encapsulation of a targeted agent, relies on the choice of capsule core and shell material that can both influence the impact on the cementitious material as a whole, and the cracks closure. These systems, able to cope with different crack widths, may lead to improvements in terms of structure durability and a consequent reduction in the frequency of maintenance activities. Nevertheless, the production of microcapsules to be included in the concrete matrix encounters scaling challenges. However, membrane emulsification emerges as a potential solution, offering scalability and consistent product quality that could match industrial demand. In this framework, the present work investigates the environmental sustainability of the aforesaid technology through a Life Cycle Assessment (LCA) analysis. The study has been conducted using a cradle-to-gate system boundary to evaluate the environmental performance of the production process of the microcapsules, contributing valuable insights towards their impact on sustainability of self-healing cementitious systems.

   8. Reusing and Recycling Superabsorbent Polymers for Sustainable Sealing and Healing in Cementitious Materials

      Didier Snoeck

      Abstract

      Currently, there is a lot of focus on sustainability and circularity in the built environment to increase its durability. Some solutions, such as adding superabsorbent polymers to induce sealing and healing effects in cementitious materials, require the use of derivatives from the petroleum industry. Although these polymers are added in small amounts, they are environmentally unfriendly due to the carbon emissions associated with their fabrication. These polymers are used in the hygiene industry and often end up in waste landfills. However, they can be recycled and reused. This paper explores the use of recycled SAPs in cementitious materials and investigates whether they can achieve similar properties and characteristics, such as regaining impermeability and visual healing. The polymers are obtained by recycling diapers and hardened cement paste containing the polymers. Both virgin and recycled superabsorbent polymers showed reduced permeability compared to reference sample, with the virgin one performing slightly better than the others. The healing process was more visible in the specimens containing superabsorbent polymers compared to the reference samples, and the trends were consistent across all specimens. However, there was a minor decrease in the overall swelling properties of the recycled superabsorbent polymers. Both the commercial and recycled superabsorbent polymers yielded comparable results in terms of reduced compressive strength. The study demonstrates the potential of reusing superabsorbent polymers for more sustainable sealing and healing of cementitious materials. Future research will investigate the complete life cycle assessment associated with overall durability.