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2020 | Book

Rheology and Processing of Construction Materials

RheoCon2 & SCC9

Editors: Prof. Viktor Mechtcherine, Prof. Dr. Kamal Khayat, Egor Secrieru

Publisher: Springer International Publishing

Book Series : RILEM Bookseries


About this book

This book gathers the peer-reviewed contributions presented at two parallel, closely interconnected events on advanced construction materials and processes, namely the 2nd International RILEM Conference on Rheology and Processing of Construction Materials (RheoCon2) and the 9th International RILEM Symposium on Self-Compacting Concrete (SCC9), held in Dresden, Germany on 8-11 September 2019. The papers discuss various aspects of research on the development, testing, and applications of cement-based and other building materials together with their specific rheological properties. Furthermore, the papers cover the latest findings in the fast-growing field of self-compacting concrete, addressing topics including components’ properties and characterization; chemical admixtures, effect of binders (incl. geopolymers, calcined clay, etc.) and mixture design; laboratory and in-situ rheological testing; constitutive models and flow modelling; numerical simulations; mixing, processing and casting processes; and additive manufacturing / 3D-printing. Also presenting case studies, the book is of interest to researchers, graduate students, and industry specialists, such as material suppliers, consultants and construction experts.

Table of Contents


Materials Science and Design

Influence of Waste Tire Rubber on Fresh and Hardened Properties of Self-Compacting Rubberized Concrete (SCRC)

This study investigates the influence of waste tire rubber on fresh and hardened properties of self-compacting concrete (SCC). Seven different SCC mixtures were designed: the reference mixture was made with natural aggregate and six SCC mixtures made with 5%, 10%, 15%, 20%, 25% and 30% replacement level of total aggregate volume. Natural fine aggregates were replaced by recycled waste tire rubber with maximum grain size of 4 mm. Flowability, viscosity, passing ability and porosity of fresh SCC mixtures were determined by means of slump flow, L-box, J-ring and air content – pressure method. Mechanical properties of hardened SCC were evaluated by means of compressive strength, flexural strength and static modulus of elasticity, while durability was expressed with two SCC hardened state properties, water permeability and gas permeability. The test results reveal that waste tire rubber affects the fresh and hardened SCC properties. With a higher amount of waste tire rubber in concrete mixtures, degradation in SCC fresh and hardened properties was observed. However, the addition of waste tire rubber up to 10% of total aggregate volume shows that it is possible to implement recycled rubber in SCC and to successfully satisfy both fresh and hardened SCC properties.

Robert Bušić, Ivana Miličević
Novel Mix Design Methodology for Self-Compacting Steel-Fiber Reinforced Concrete Based on Rheological and Mechanical Concepts

We describe a new methodology to calculate mix proportions of components for self-compacting steel-fiber reinforced concrete [Construction and Building Materials 189 (2018) 409–419]. The methodology is based on a previous one for plain self-compacting concrete by Prof. B. L. Karihaloo and co-workers, which has been expanded to include steel fibers while maintaining self-compactability of the concrete. The methodology has two key points. The first one is the rheological behavior of the fresh material, which leads to considering the effective viscosity of the suspension with fibers as a design parameter. By means of micromechanical models we estimate this parameter from the plastic viscosity of the cement paste and the volume fraction and aspect ratio of the fiber. The second one is the desired compressive strength of the composite material, which leads to setting water-cement ratio as the other design parameter. Besides, water-cement ratio influences the plastic viscosity value of the cement paste, together with the content of superplasticizer admixture. This rheological parameter has to be measured by means of rheometers or approximated by other simpler and cheaper instruments, like capillary viscometers (Cannon-Fenske or Marsh funnel). The methodology has been programmed numerically in MATLAB to make some practical design charts by means of which the quantities of the concrete components are calculated. The use of these design charts is explained with an example. The study also provides experimental validation in fresh and hardened state. The results show the robustness of the proportioning methodology.

Ángel de la Rosa, Elisa Poveda, Gonzalo Ruiz, Héctor Cifuentes
Innovative Use of Fine and Ultrafine GCC in Cementitious Systems

Ground Calcium Carbonate (GCC) has been used for decades in construction to enhance performance-cost ratio of cement-based products such as grout, mortar or concrete. From dry-mortars to structural concrete, engineers associate GCC with cementitious materials (SCM) to optimize the fluidity, viscosity and reduce the carbon footprint of the mixtures. Nevertheless, the contribution of GCC to the flowability and viscosity of the cement-based systems as well as the range of GCC fineness available to optimize the packing density and strength are poorly appreciated. The benefits of specific GCC products are expected to be particularly useful in formulating concrete or mortar for digital fabrication. This paper will provide an overview of the best practice use of GCC products, aiming to stimulate interest for the material not only for use in digital fabrication with concrete.

Pascal Gonnon, Philipp Mueller, Thomas Lys
Use of Surfactant to Improve Properties of Crumb Rubbers in Concrete Products

Use of crumb rubbers from waste tires in concrete applications can help reduce environmental impacts from the massive waste tires. However, several studies show that incorporating crumb rubbers into concrete can decrease the mechanical properties due to their low strength and stiffness, and poor interfacial bond with cement paste. Since crumb rubbers are considered a hydrophobic material, they tend to repel water and segregate from fresh cement paste. This causes poor bond strength between cement paste and crumb rubbers and provides negative effects on concrete strength. This study aims to improve the performance of concrete mixed with crumb rubber or rubberized concrete by increasing the crumb rubber surface wettability (i.e., reduce its water repellant ability). A surfactant (Tergitol NP-10) is applied to the crumb rubbers in order to reduce solid/liquid interfacial tension between the crumb rubber and water. This modification should allow better attachment and bond between crumb rubbers and cement paste and hence, improve the concrete mechanical properties. The specimens are prepared using non-modified and modified crumb rubbers at the rate of 3% to 10% by volume. Three experiments are a carried out: adhesive bond, compressive and flexural strength. Results show that the rubberized concrete mixed with modified crumb rubbers exhibit better bond and higher compressive and flexural strengths than those mixed with conventional crumb rubber.

Marupatch Jamnongwong, Piti Sukontasukkul
Structural Build-Up of Cementitious Paste Under External Magnetic Fields

Engineering application processes of fresh concrete include transporting, pumping, formwork casting, etc. Each process is a significant factor influencing properties of fresh and hardened concrete. However, many contradicting requirements of fresh concrete performances (such as structuration rate) exist in these operation processes. Therefore, advanced techniques need to be proposed to satisfy future challenges. Actively controlling the stiffness by applying external magnetic fields would be a potential solution for the contradicting requirements, and could make the pumping and casting processes smarter and more reliable. In the present paper, the effects of magnetic field strength and magnetizing time on structural build-up of cementitious paste are discussed. The results show that higher magnetic field strengths result in higher percolation time and lower phase angle at equilibrium state. However, the application of external magnetic fields with low flux density has little effects on the viscoelastic behaviour of cementitious paste. Under high magnetic field strengths, the viscous-liquid behaviour dominates the elastic-solid behaviour at early stage, while the solid-like behaviour becomes more dominant with magnetizing time.

Dengwu Jiao, Khadija El Cheikh, Karel Lesage, Caijun Shi, Geert De Schutter
Influence of Aggregate Particle Size Distribution on Mixing Behavior and Rheological Properties of Low-Binder Concrete

Particle Size Distribution (PSD) has impact on the workability of concretes because it affects the particle packing and particle mobility during flow. In continuous concrete production, keeping always the same PSD is not possible. So, it is important to understand how this variability affects concrete properties. The research described in this paper evaluated a more sustainable low-binder concrete, with focus on particle size variability of the aggregates. Applying particle packing and dispersion concepts, rheological control, use of limestone fillers and appropriate choice of material, a reference concrete with low binder consumption (3.7 kg/m3/MPa) was developed. On this reference concrete, PSD variations were applied: a coarser and a finer version for each aggregate was tested and two levels of fines content were also evaluated. Mixing behavior and rheological properties were determined by a concrete mixing rheometer (Pheso Poli-USP) with planetary configuration. An acceptance criterion was established based on mixing torque and all concrete outside the limits had their water content adjusted until they met the specifications. After that, mechanical strength was evaluated at 28 days of age. The obtained results indicate that PSD variations affected both the mixing and flow of concrete. Especially higher fines content and presence of a finer natural sand increased the torque levels during the mixing process and shear cycles and lead to higher mixing power demand. The water correction, adopted to overcome the rheological changes, affected hardened state properties (up to 10% on compressive strength). As these findings are specific to the analyzed concrete and considered PSD variations, this research aimed to explain more generally the influence of the several variables. The surface area of the granular material, solids concentrations and mean distance between the fine and coarse particles are some quantitative parameters useful for predicting rheological aspects of concrete compositions.

Markus Samuel Rebmann, Rafael Giuliano Pileggi
Suspensions Sedimenting in a Horizontal Annulus – A Model for Oilfield Cements in Horizontal Wells

We evaluate the settling of a suspension in an annular geometry, where the concentric pipes are placed horizontally. The geometry was chosen to mimic cement slurry bleeding (i.e. accumulation of fluid on top of the geometry due to the settling of particles) in horizontal oil and gas wells. We compare the behavior of ideal semi-dilute suspensions, such as polymer beads in oil, with real cement slurries, in cells of similar geometry. Despite the differences between the two systems, our results show striking similarities and explain the presence of weak points at the upper outer diameter, below the internal diameter and at the poles.

Agathe Robisson, Teresa Liberto, Elizabeth B. Dussan V.
SCC for Sub-Saharan Africa Based on Local Raw Materials – Material Development, Optimisation, and Application Concept

Sub-Saharan Africa’s (SSA) economies are developing at rapid pace. To keep up the verve, housing and infrastructure are urgent challenges, which demand for concrete technologies that can meet the demand. Considering the climate challenges that come along with concrete construction, for the growing African construction business, it is inevitable to use binders with lower carbon footprint and to use chemical admixtures that help reducing cement in concrete. The use of superplasticizer (SP) and stabilising agents (STA) can enhance the concrete technology in SSA, since they can make concrete quality independent of the boundary parameters. However, the use of cement and concrete additives depends on their availability. Due to the partly poor infrastructure and the lack of chemical industries, in most regions in SSA, the use of admixtures is not yet always common practice. This amplifies the unfavourable framework for concrete construction such as fragmentary supply chains, high local cement prices, and unfavourable construction site facilities in this region significantly.After providing a general overview of the peculiarities of the SSA boundary framework, and the recommendation of pre-mixed self-compacting concrete (SCC) compounds as a tool to overcome local challenges, a three-step SCC optimisation concept is recommended and experimentally proven based on readily available additives on the African continent. Eventually, the paper elaborates on alternative polysaccharide based rheology modifying agents from agricultural resources and waste materials with high potentials for high-performance concrete applications in SSA.

Wolfram Schmidt

Effect of Supplementary Cementitious Materials, Fillers and Chemical Admixtures on Rheology

Effect of Sodium Sulphate on Rheological Behaviour of Alkali Activated Slag Binders

Alkali-activated binders (AABs) are alternative binders to OPC which can reduce carbon emissions. AABs use a precursor (mostly a by-product) and alkaline activator that produces a binder having cementitious properties. However, a few drawbacks like faster setting time and high drying shrinkage hinders their application on a larger scale. The time available to work at ease with these materials depends on the kinetics of the reaction and rate of flocculation; which in turn is dependent on composition of the precursor, solid content, type of activator and activator dosage. The amount of calcium present in the precursor is one of the factors that govern the early reaction kinetics. Similarly, the concentration and type of alkali ions in the system have a significant effect on rheological behavior. In order to use AABs in large scale applications, it is essential to understand the effect of various parameters on the workability of mixtures. The objective of this study is to evaluate the effect of sulphate content on the rheological behavior of alkali-activated slag binders and it was found to have a significant effect on the evolution of yield stress and apparent viscosity.

Aparna Sai Surya Sree Nedunuri, Salman Muhammad
Bio-Derived Rheology Modifying Agents for Cement-Based Materials

In recent few years, significant development has been made in concrete technology to accommodate the requirements of high-performance concrete. Rheology Modifying Agents (RMAs) (such as superplasticizers) and Viscosity Modifying Agents (VMAs) have been developed as two alternative admixtures to obtain the required workability. However, these admixtures not only increased the environmental impacts of concrete production but also increased the unit cost of concrete. Following these concerns, several studies have been focusing on exploring more sustainable approaches in concrete production such as the use of bio-based admixtures in concrete production. Throughout the literature, bio-based polysaccharides (cellulose, chitosan, etc.) were found to be highly effective as VMAs. Long chain molecules of these polysaccharides stick to the water molecules, decrease their relative motion and forms a gel, so increase the yield stress and plastic viscosity. This behaviour reduces the bleeding and segregation, which results in robust highly workable concrete.The interest in this study was motivated by the vital demand to introduce a greener and more sustainable VMA to improve the rheological properties of cement paste. To this end, bacterial cells proposed as VMAs for cement-based materials. The bacterial cells were directly incorporated into the mix of water without any additional intervention. The rheological measurements were implemented to evaluate the influence of cells on apparent viscosity and yield strength. In addition, the use of superplasticizers and fly ash on the performance of biological VMA were also investigated. Our results showed that the apparent viscosity and yield stress of the cement-paste mix were increased with the addition of the microorganisms. Moreover, bacterial cells were found to be compatible with the use of both fly ash and superplasticizers.

Mahzad Azima, Zeynep Başaran Bundur
Influence of Cements Containing Calcareous Fly Ash on Rheological Properties of Fresh Mortars and Its Variability

In the research influence of cements containing calcareous fly ashes W as non-clinker constituent produced by different methods on rheological properties of mortars and its variability is presented. In comparison to mortars with CEM I mortars with cements CEM II/A-W, CEM II/B-W, CEM IV/B-W are characterized by worse workability and faster workability loss, the greater the more fly ash W is in cement. However, using cements CEM II/A-W, CEM II/B-W produced by intergrinding of the constituents or homogenization with ground fly ash W it is possible to obtain mixtures with acceptable rheological properties. Obtained results shows significant influence of properties of the fly ash W on the variability of rheological properties of cement CEM II/B-W mortars. However, if fly ashes W with a bulk density of less than 900 kg/m3 are not used for the production of cement, it is possible to achieve variability of the rheological properties of mortars, to a level not deviating significantly from other types of cements.

Jacek Gołaszewski, Tomasz Ponikiewski, Aleksandra Kostrzanowska-Siedlarz
Early Properties of Portland Cements with Varied Set Regulators

The effects of variation of amount and type of calcium sulfate on the early behaviour of hydrating Portland cement were examined. Initial setting of pastes determined via the Vicat needle penetration method indicates that not only the amount but also the type of set regulator has a substantial impact on early properties of hydrating cement. The influence of the type not only depends on its concentration but also on the Portland cement clinker used. In the measurement of ultrasonic P-wave velocity of hydrating pastes, different stages of strength gain can be defined. The successive addition of set regulators changes the material properties in these stages in different ways. Examinations lead to the conclusion that differences in the prepared samples are mainly due to different solubility of calcium sulfate types, early ettringite formation and the amount of reacting aluminate phases of the clinker.

Tamino Hirsch, Tobias Dorn, Dietmar Stephan
Influence of Different Accelerators on the Rheology and Early Hydration of Cement Paste

Special applications like pumping, spraying or printing of concrete require the precise adjustment of very specific rheological properties at different time steps during the casting process. Superplasticizers such as polycarboxylate ethers (PCE) can be used to obtain the required flowability, which, possibly in combination with additional rheology modifying admixtures, generate the required specified consistency. However, after the application, the concrete should change the rheological properties immediately in order to avoid deformations at rest. Therefore, the use of accelerators can be effective. Accelerators influence the hydration of cementitious materials, and thus the rheological properties over the course of time and the setting.In this paper, the influence of different accelerators on the rheology and early hydration of cement paste as well as the interaction of accelerator and PCE are presented. Methods like rheometry, needle penetration tests and practical tests like spread flow were applied. The used accelerators showed accelerating behavior on the cement pastes without and in the presence of PCE. At the same time an influence on the rheology could be observed. This effect was less in the mixes with PCE, especially at the highest water/cement ratio (w/c).

Sarah Leinitz, Zichen Lu, Simon Becker, Dietmar Stephan, Regine von Klitzing, Wolfram Schmidt
Effect of Mineral Additions on Rheology and Fresh Properties of Cement Pastes and Mortars

In this study the following mineral additions were used as 10% by weight cement replacement: silica fume SF, two types of metakaolin MK1 and MK2, and limestone powder LP. One type of cement CEM I 42.5R and one high range water reducing (HRWR) admixture were used in all mixes. Fresh properties of mortars with natural postglacial sand 0/4 mm were examined by mini-cone test and rotational viscometer Viskomat XL. In this instrument, when the cylindrical sample container rotates, the mortar flows through the blades of the impeller and exerts a torque which is measured by a transducer. As a result of the measurement, a set of data expressing the resistance of the mix subjected to the stresses induced by the rotation of the impeller was obtained. By linear approximation of the obtained results from the down-curve, the flow line of the mixture was obtained and compared with the modified Bingham Equation, which allowed to determine the rheological parameters of the tested mortars. All additions except for LP decreased rheological properties of the tested pastes and mortars. Not only particle size distributions (PSD), cumulative percentages and specific surfaces of the powders influence water and admixture demand of cement-based composites. Also shape and texture of the individual particles have an effect on the rheological properties.

Dorota Małaszkiewicz, Mateusz Osipiuk
Effect of the Side Chain Density and Length of Polycarboxylate Ether Superplasticizers on the Thixotropic Structural Build-Up of Cement Paste

Polycarboxylate ether superplasticizers (PCE) are of great importance to control interparticle interactions and hence the rheological properties of cement-based suspensions because their molecular structure can be modified according to the requirements. Nevertheless, the effect of individual parameters of the molecular structure on thixotropy is not yet fully understood. For a deeper understanding, specifically polymerized PCE with different side chain densities and side chain lengths were investigated. The effect of the molecular structure was studied by producing cement pastes with constant yield stress and determining the thixotropic structural build-up with a parallel plates rheometer.The results indicate that thixotropy increases with decreasing side chain densities and decreasing side chain lengths. This might be explained by the fact that PCE molecules with low side chain densities adsorb faster and to a larger extent on cement particles surfaces. Consequently, less PCE molecules are left in the pore solution to enable permanent adsorption on newly formed and growing hydration products, leading to a decrease of steric repulsion and hence to an increase in thixotropy. Furthermore, thixotropy increases in case of lower side chain lengths. This effect might be related to a decreased PCE layer thickness on the cement particle surface, increasing the probability to be overgrown by hydration products.

David Nicia, Dirk Lowke
Interaction of Superplasticizers with Cement from the Point of View of Colloid Chemistry

When cement is mixed with water, the clinker phases immediately start to dissolve and a large amount of ions is released into the pore solution. As a result, the ion concentration rapidly increases until the aqueous phase is supersaturated, at which first hydration products are precipitated. As the dissolution, crystallization and the initial hydration reactions all occur at the solid-liquid interface, it is appropriate to consider early cement hydration from the aspects of colloid and interface science.Generally, fresh cement pastes constitute a thermodynamically unstable colloidal dispersion of mesoscopic particles and hydrate phases in water. The rheological properties (e.g. viscosity, yield stress) and the stability are affected by colloidal and interparticle interactions (e.g. Brownian effects, hydrodynamic and contact forces). However, the poor workability of cement suspensions can be attributed to attractive van der Waals forces between cationic and anionic surface areas. To overcome those forces, superplasticizers are added which disperse cement by imparting an electrostatic (polycondensates) or steric (polycarboxylates) effect. Superplasticizers can interact with cement via adsorption (=physisorption), chemisorption (=intercalation into early hydrate phases) or at low water-to-cement ratios even through repulsive depletion forces induced by the portion of non-adsorbed polymers remaining in the pore solution.In light of this, the aim of the paper is to give an overview of the different kinds of interactions of superplasticizers with cement from a colloid chemistry point of view. It will be shown, to which thermodynamic parameters the adsorption process is subjected and how the chemical composition of the polymers affects the adsorption behavior. Additionally, experimental methods will be presented that are commonly applied for the investigation of cement-superplasticizer interactions (adsorption and zeta potential measurements). Finally, the role of non-adsorbed superplasticizer molecules on the dispersion of cementitious systems with high solid volume fractions will be discussed.

Johann Plank, Manuel Ilg
Improvement of UHPFRC-Rheology by Using Circular Shape Memory Alloy Fibres

Fibre reinforcement of Ultra-High Performance Concrete (UHPC) is linked to a reduction of the flowability of fresh concrete. Moreover, high fibre contents often promote agglomerations. Therefore, commonly a fibre content of about 1–2 vol.-% is used. A novel method is proposed to minimise the negative influence of high fibre contents on the rheological properties of fresh concrete without any significant deterioration of the mechanical properties of the hardened concrete. To achieve this, shape memory alloy (SMA) fibres made from nickel and titanium are proposed to be used. These SMA-fibres have the ability to transform into an imprinted geometry upon heating. During mixing, fibres with a circular geometry avoiding agglomerations are added and, therefore, the rheological properties of fresh concrete can be improved compared to straight fibre reinforced concrete. After mixing the UHPC, the shape memory effect is thermally activated while the concrete is still flowable. The fibres transform into their imprinted, straight geometry enhancing the properties of the hardened concrete. With this method we propose to combine the improved mechanical properties of a fibre reinforced UHPC with a good workability. The present work presents a first step towards achieving the final goals.

Maximilian Schleiting, Alexander Wetzel, Florian Gerland, Thomas Niendorf, Olaf Wünsch, Bernhard Middendorf

Laboratory and In-Situ Rheological Testing

The Use of Parallel-Plate Rotational Rheometry to Determine the Superplasticizer to be Used in Cement Pastes Admixtures

The usual test to obtain the better superplasticizer (SP) to be used and also their content in the admixture is the Marsh cone test, but it demands a lot of material to perform it. On other hand, the use of the parallel-plate rotational rheometry allows achieving those answers using very few materials and in a fast way. In this research, three different pastes were tested to see which one had the longer workability period, performing oscillatory time sweep test. This test allows observing the behavior of the elastic component (G′) in the time, fact that some authors correlated with the setting time. After choosing the SP that obtained the best behavior over time, flow tests in pastes with different amounts of additive were performed to obtain the saturation point. With the viscosity results, it was possible to analyze when the SP no longer influences this parameter. It was observed that very few materials were used in these tests, an important factor when working with expensive or rare materials. Determining the superplasticizer that did not indicate delay in casting time and their saturation point, could guarantee that the additive did not affect the compatibility between materials in the admixture.

Livia B. Agostinho, Eugenia F. da Silva, Luciana A. Farias, Alexandre C. Pereira
Rheology and Build-Up of Fresh SCC Pastes Evaluated with the Mini-slump Cone Test

SCC are composed by a larger amount of paste than conventional concrete in order to achieve larger flowability without segregation. SCC pastes are typically very fluid, showing large spread diameters in consistency tests, while exhibiting high viscosity values. In this study, a mini-slump cone test is used to evaluate the fresh properties of SCC pastes with different supplementary cementitious materials (SCM), as limestone filler (LF), colloidal nanosilica (NS) and metakaolin (MK). Two amounts of NS were studied and different amounts of Superplasticizer (SP) were considered to achieve self-compacting ability. The mini-slump test has been implemented with a video acquisition setup that records the spread diameter and allows to follow the velocity of deformation of the fresh paste. The basic rheological parameters were calculated using simple analytical models obtained from the literature. The effects of the type and amount of SCM and the level of SP were analyzed. Several cones were filled in each batch and tested at different times after cast, comparing samples at rest with other stirred before testing. The comparison of both results allowed to identify the structural build-up and the reversible/irreversible processes that take place in the fresh SCC pastes and the effect of SCM and SP.

Gonzalo Barluenga, Irene Palomar, Cynthia Guardia, Hugo Varela, Francisco Hernandez-Olivares
About the Influence of Shear-Induced Particle Migration and Sedimentation on the Measurement Results of Concrete Rheometers

Concrete chemistry is an integral component in the development of eco-concretes, easily compactible concretes, high-strength and very durable concretes. It is always necessary to adapt the fresh and hardened concrete properties to the respective application. In order to be able to develop a specific mix design, two essential requirements have to be taken into account. Firstly, mixing technology must also be reproduced on a laboratory scale. Secondly, the fresh concrete properties must ideally be determined in absolute units. A so-called intensive mixer is preferred in order to map the various mixing technologies used in practice. The shear intensity and thus the machine’s Froude number can be changed over a wide range. A rheometer, which uses so-called absolute measuring tools, enables the calculation of the fresh concrete properties in absolute units. The KNIELE KKM-RT 22.5/15 integrates a rheometer into an intensive mixer. This unique combination is extended by a device for pre-shearing and homogenization of the mixture. In this article it will be shown that the mix is segregated during classic pre-shearing and that the subsequent measurements deliver too low raw data. The rheological parameters calculated from these raw data are too low and do not describe the concrete correctly. Pre-shearing with the newly developed device eliminates this fundamental problem of other concrete rheometers.

Christian Baumert, Harald Garrecht
On-Board Concrete Rheology Measurements Using an In-Drum Sensor System: Early Stages

Consistent quality in concrete production is an essential requirement in the ready-mix concrete industry. Insuring batch-to-batch uniformity is, in fact, an ever-present challenge. Moreover, modern concretes mixture designs often have complex behaviors in their fresh states, and yet the focus is on the slump (related to the yield stress) only, presenting an incomplete picture when one wants to assess the properties of various types of concrete. A second parameter known to be highly informative in this situation is the plastic viscosity of the fresh concrete. Few authors have assessed the potential of rheology measurements with a ready-mix truck. After a short introduction on sustainability, the aim of the first part of this conference paper is to offer a review of the different methodologies and results available on rheology measurements in/with a ready-mix truck. The second part is focused on the description of the in-drum sensor system used in this project. Finally, methodology and results about the slump evaluation with the in-drum sensor system are presented.

Xavier Berger, Pierre Siccardi, Robin Jean, Marc Jolin, Denis Beaupre, Benoît Bissonnette
Experimental Developments of the Squeeze Flow Test for Mortars

Squeeze flow rheological technique is based on the compression of a cylindrical sample between parallel plates and is used to determine the flow properties of food, pharmaceuticals, composites, suspensions, including cementitious materials. This work summarizes the main experimental developments on squeeze-flow for the evaluation of mortars that have been performed in Brazil for the last 15 years and supported the creation of the Brazilian standard test method applied to rendering and masonry mortars (ABNT NBR 15839:2010). The paper exemplifies possible test setups (configuration, geometry, velocity, roughness) for different types of mortars and situations, the use of porous substrate (ceramic or concrete blocks) as the bottom plate, and a method to measure phase separation induced by the. A complementary instrumentation (interfacial pressure mapping) for the assessment of pressure evolution during flow is also presented – forming the pressure mapped squeeze flow method (PMSF) – which allows for identification of transitions in flow type and localized pressure peaks resulting from microstructural changes like particle jamming. The technique was also employed to study and develop laboratory mixing methods for mortars, as the resulting flow curves are very sensitive to the material’s agglomeration state. Finally, rheological parameters of mortars by squeeze-flow and rotational rheometry were compared showing that yield stress have some degree of agreement, whereas viscosity values from these techniques are complex to be related.

Fábio A. Cardoso, Franco A. Grandes, Victor K. Sakano, Andressa C. A. Rego, Fábio C. Lofrano, Vanderley M. John, Rafael G. Pileggi
Measuring the Impact Behavior of Fresh Mortars by Pressure Mapping

Mortars and concretes are subjected to diverse rheological situations during their processing and application. Their behavior can be predicted for most situations by rotational rheometry and/or squeeze flow. However, very high strain rates that occur during impact are very difficult to be properly simulated using these methods. Especially for rendering mortars, impact behavior (during manual or spray application) is important not only regarding productivity and rebound issues but also because the initial mortar-substrate contact extension strongly affects the interfacial bond strength, which is one of the renders most critical hardened properties. The present work introduces initial developments towards an impact rheometry technique intended primarily for cementitious and other suspensions used in construction. The technique is based on a pressure mapping system that measures area and force with a thin and flexible sensor at 100 Hz. Mortars were applied manually, by continuous spraying, and by free fall. Results showed that in manual application, pressures up to 50 kPa took place, whereas in the mechanical procedure the pressure values were considerably lower (>5 kPa) since the force is distributed in small portions of material by the spray. Some of these results can be useful to compare projection techniques and equipment, for the development of nozzles, and to set free fall drop heights to better simulate manual applications and even allow more realistic molding procedures for mortar-substrate tensile bond tests.

Victor K. Sakano, Franco A. Grandes, Fábio A. Cardoso, Fábio L. Campora, Roberto C. O. Romano, Rafael G. Pileggi
Evaluation of Fresh Adhesive Mortars Through Various Rheological and Imaging Techniques

Adhesive mortars are meant to glue tiles and during application they are applied with a toothed comb to ensure that the proper amount of material is distributed over the substrate, also to ease the later tile placement. Throughout the application, different types of strains and stresses are imposed to adhesive mortars, and one method is not enough to fully characterize their behavior. Thus, in this investigation various techniques were used to evaluate the mortar’s fresh properties. Bulk and interfacial oscillatory rheology combined with MRI characterizations were used to understand the rheological properties evolution and skin formation over time simulating the waiting period until the tile is emplaced. Squeeze flow measurements at different waiting times were used to indicate mortars behavior during tile placement and were complemented with small depth-of-field optical microscopy technique to obtain the visualization of the contact between mortar and tiles. The experimental variable studied was the content of cellulose ether – widely used admixture in adhesive formulations as viscosity and water retaining enhancer – and the applied methodology was able to assess the effects of the admixture by covering a wide range of the required fresh properties of adhesive mortars.

Alessandra L. Fujii-Yamagata, Fábio A. Cardoso, Anne Daubresse, Evelyne Prat, Mohend Chaouche
Evaluation of Structural Build-Up Rate of Cementitious Materials by Means of Constant Shear Rate Test: Parameter Study

Accurate characterisation of static yield stress evolution with time enables correct evaluation of the structural build-up rate for cement-based materials. This parameter is fundamentally important for many construction processes, including conventional in-situ concrete construction, various digital fabrication techniques, well cementing, etc. The paper at hand presents a parameter study on determination of structural build-up by means of constant shear rate test. It is shown, how the choice of single or multiple samples as well as different constant shear rates and pre-shear regimes influences the apparent time-dependent static yield stress evolution of cementitious materials and, hence, the accuracy of structural build-up rate evaluation. Respective recommendations for decreasing error in measurements of static yield stress are provided.

Irina Ivanova, Viktor Mechtcherine
Comparing Phase Development and Rheological Properties of OPC Paste Within the First Hour of Hydration

In this paper the very early hydration of ordinary Portland cement at 20 °C and 30 °C is investigated, focussing on the first hour after the addition of water. The development of the rheological behaviour of cement paste during hydration is compared with the kinetics determined by quantitative in-situ X-ray diffraction (QXRD) and heat flow calorimetry. For both temperatures the cumulative heat correlates very well with the evolution of ettringite content over the first hour of hydration. The precipitation rate of ettringite is strongly influenced by temperature. This results in a higher formation rate of ettringite already in the first minutes after mixing at 30 °C. Analogously the temperature affects the rheological behaviour of the cement paste. The measured torque values are also higher for 30 °C from the first point of investigation on. Furthermore, the increasing torque can be linked to the rise in the ettringite content at both temperatures. The formation of other hydrate phases influencing the development of the rheological behaviour within the observed time frame cannot be proven with the data at hand. Therefore, it can be assumed that ettringite content is the determining mineral for the early workability of cement pastes.

Cordula Jakob, Daniel Jansen, Ursula Pott, Jürgen Neubauer
Challenges in Rheological Characterization of Cement Pastes Using a Parallel-Plates Geometry

Cement-based materials are characterized as complex suspensions that may experience a thixotropic behavior caused by physical and chemical phenomena. The characterization and understanding of the rheological properties of cement-based materials have become essential with the introduction of 3D printing in field of civil engineering. Therefore, there is a need to accurately measure such properties to obtain repeatable and consistent results. To measure the rheological properties, different geometries are available, such as vane, parallel-plates, or coaxial cylinders: These are the most used for cement-based materials. Although, there are no specific guidelines on how to select the appropriate geometry for the material that will be tested. Proper understanding of the advantages and disadvantages as well as the limitations of each geometry should be taken into account. Since parallel-plates is a common tool used to evaluate fresh cement-based materials, due to its simplicity, the small sample volume required and the variable gap that can simulate the distance between the aggregates. This paper discusses the major challenges and issues encountered when using parallel-plates geometry to measure the rheological properties of cement-based suspensions under shear. Some issues such as wall slip, sample spill, dryness, particles sedimentation, non-uniform shear rate applied, etc. can be prevented but the user should be aware of these problems.

Aida Margarita Ley-Hernández, Dimitri Feys
Correlation Between “Very Early” Age Fracture Performance and Evolution of Rheological Properties of High Performance Fiber Reinforced Cementitious Composites with Adapted Rheology

The tremendous advances in concrete technologies our society is witness of, do not only provide the construction industry with new advanced materials and processing/manufacturing techniques, but also require the performance of cement based materials to be investigated not only in its structural service state, but also throughout its very early and early age life.Tailored successful placement and development of mechanical performance, even in the first hours of life, can affect the structural durability and discriminate about the successful accomplishment of the structural performance throughout the service life. In this paper reference is made to a High-Performance Fibre-Reinforced Cementitious Composite, formulated with adapted rheology to ease its placement and most of all to achieve a tailored alignment of the fibres through the casting flow.The development of tensile and shear fracture properties in the first hours (up to three) after the first contact between cement and water has been studied with an ad-hoc designed test set-up. The knowledge of such properties is of the utmost importance to foster the use of these kind of advanced cement based materials with adapted rheology in precast construction, where the design of transient situations, including demoulding and handling, may play a crucial role, also in the sight of optimizing the productivity.In a quality control framework, the development of tensile and shear fracture properties of the investigated materials in the considered time frame have been also correlated to the evolution of rheological properties, so far evaluated through a mini-slump flow tests.

Francesco Lo Monte, Gabriele Zago, Marco Cucchi, Liberato Ferrara
Investigation of the Early Cement Hydration with a New Penetration Test, Rheometry and In-Situ XRD

To gain more information about the relationship between early cement hydration and rheological behavior of the corresponding cement paste, a new penetration test device, with the name “Multipurpose Incremental Loading device” (MILD), has been developed. The construction and the mechanical properties of the device are described in detail. Furthermore, the implementation of a measurement and first results will be discussed, and the new device is compared with the standardized Vicat test. In addition, a comparison of the measurement results with rheological investigations is made and the results of quantitative in-situ XRD and calorimetry are integrated for a deeper understanding. We show that it is possible to get more information about the structure formation with the new device than with the Vicat test. Moreover, a comparison with the rheological properties of a cement paste was done. Both methods show two periods with different rheological behavior. During the first two hours the paste shows a slow increase of viscosity which is followed by a strong increase. The results of the penetration test and the rheometer are linked with the formation of hydration products and the heat flow development. This comparison shows that the link between the two periods is the beginning of the acceleration period. Finally, it is concluded that it is possible to get precise information about the early cement hydration with a penetration test.

Ursula Pott, Clemens Ehm, Cordula Jakob, Dietmar Stephan
Use of Combined Rheo-NMR to Investigate the Relationship Between the Molecular and Mechanical Properties of Early Cement Paste Hydration

The in-situ combination of rheological measurements with solid-state NMR as a second characterization method is used to gain unique information about molecular dynamics and structure of time-dependent phenomena. This study aims to show the application of low field benchtop 1H NMR relaxometry combined with rheology to investigate the hydration and hydration kinetics of cement pastes. Here the relationship between the storage modulus, G′ and transverse, T2, 1H-NMR relaxation rates in different water environments that exist during early hydration of cement paste at different water to cement ratios is presented. In addition, the rate of rigidification and percolation time are determined from the dynamic time sweeps at a strain within the linear viscoelastic region.

Nonkululeko W. Radebe, Karl-Friedrich Ratzsch, Christopher O. Klein, Manfred Wilhelm
Calibration of ASTM C230 Cone for Measuring Flow Diameter of Self-flowing Mortar According to the EFNARC Recommendation

Proper design of mixing proportions is the key factor to appreciate the benefits and advantages of self-compacting concrete (SCC). Determining a proper water-to-powder ratio is a crucial step in designing SCC. Mini slump flow test of mortar, as recommended by the EFNARC, is popularly used to check the water-to-powder ratio in the design process. The dimensions of the EFNARC recommended cone is slightly different from the widely available ASTM C230 cone. This study is an attempt to find a correlation between the test results of these two cones. Using the same fresh mixtures, two sets of data were collected using both cones. The correlation factor was determined using these data and verified by theoretical calculation. A proper correlation will allow the use of ASTM cone in the design of SCC. As the ASTM recommended cone is commonly available in most concrete laboratories, its application in SCC related studies will reduce the need of fabrication of new equipment, as well as, using the same cone to test the slump flow of both conventional workability and self-compacting mortar will allow the experts to come up with simplified test procedures and guidelines for the fresh property of mortar for the whole workability range.

Shamir Sakir, Sudharshan N. Raman, A. B. M. Amrul Kaish, Azrul A. Mutalib
Thixotropy-Dependent Form Filling Ability of Cement Paste

The form filling ability of fresh concrete is not only dependent on its rheological parameters yield stress and viscosity but on thixotropy as well. Currently, there are not many investigations regarding the effect of thixotropic structural build up on the form filling behaviour of concretes. The thixotropy of fresh concrete is mainly dependent on the thixotropic character of its cementitious paste. Thus, form filling experiments on cementitious suspensions were performed investigating their workability in dependence of their rheological parameters as preliminary tests for the workability prediction of fresh concretes. For this reason, cementitious pastes with equal solid content but varying yield stress and thixotropy were tested. Rotational rheometer measurements to investigate the rheological key parameters yield stress, viscosity and thixotropy were combined with formfilling tests in a L-shaped model formwork. With increasing thixotropy, flow distance in the formwork and thus form filling ability of the cementitious suspensions decreased. The conducted experimental series therefore is the base to enhance the prediction of form filling behaviour of fresh concrete.

Mareike Thiedeitz, Thomas Kränkel, Christoph Gehlen

Mixing, Processing and Casting of Mortar and Concrete

Comparative Study on the Effect of Mixer Type on Properties of Self-compacting Mortar

For the realisation of safe, permanent and sustainable solutions for the management of short-lived low and intermediate level radioactive waste in Belgium, this radwaste is placed in concrete caissons and subsequently encapsulated with mortar to form a monolith, placed in a near surface disposal facility. This high-performance self-compacting mortar consists of an inert calcareous matrix (filler and sand), blast furnace slag cement, microsilica and naphthalene sulfonate superplasticizer (dry-powder type and liquid-based type), with a water/cement ratio of approximately 0.36. As considerable amount of this cementitious material is needed, it is necessary to come to an easily manageable and repeatable mixing and casting procedure.Therefore, an intensive experimental program was conducted to evaluate the effect of different mixer types on the consistency of fresh state (slump flow, V-funnel, air content and volumetric weight), the hardened properties at different ages (both compressive and flexural strength, modulus of elasticity and coefficient of thermal expansion) and porosity accessible to water (including segregation risk). Four different mixers were considered in this study, with different working principle and capacity: (i) forced action pan mixer, (ii) ring pan mixer, (iii) paddle mixer (ploughshare), and (iv) twin shaft mixer. For durability related reasons, porosity and segregation risk have a decisive effect on the choice of mixer to be used for further (upscaled) research.It was found that the mixing procedure, scale and type has an impact on the previously mentioned properties of the self-compacting mortar. Lowest porosity is obtained by means of ploughshare mixer in combination with dry superplasticizer, while the lowest segregation risk is obtained for TS mixer, regardless the type of superplasticizer.

Bart Craeye, Wim Bastiaens, Erik Coppens, Dirk Van Houdt, Wilfried Gijbels, Thomas Rondou
Effect of Electromagnetic Pulsation on the Rheological Properties of Mortars During Pumping

The basic understanding of the underlying mechanisms and the coherences between material properties and processing parameters, which are prerequisite for a better understanding and prediction of pumpability of concrete, mortar or suspensions, is an objective of numerous research activities. Current investigations aim to actively control the pumping process, hence being able to prevent blockages. Although much progress has been made in this research field recently, generally applicable models for the prediction of pumpability under consideration of the rheological properties of the material to be pumped as well as the process parameters are not available.Experimentally determined properties of the bulk material investigated in a small scale pumping test will be presented. We evaluated the effect of an externally applied alternating electromagnetic field with varying frequencies on the pumpability of the mortars regarding changes in pressure in the pipe as well as viscosity and yield stress of the bulk material. For the tests, two mortars with a constant solid volume fraction based on limestone powder (non-reactive) or ordinary portland cement (reactive) as solid phase have been investigated. Moreover, the lubrication layer formed at the interface between pipe and material during pumping, being the main influencing factor on pumping of cementitious materials, will be examined. The effect of the alternating electromagnetic field on the lubrication layer was experimentally simulated with a sliding pipe rheometer. Results for the bulk material and the lubrication layer will be compared. Moreover, the practical applicability of electromagnetic pulsation on the pumpability will be discussed.

Inka Dreßler, Patrick Varady, Hans-Werner Krauss, Dirk Lowke
Influence of Aggregate Volume Fraction on Concrete Pumping Behaviour

The paper at hand quantifies the influence of aggregate volume fraction on pumping behaviour of concretes with distinct flow behaviours, i.e. plug or shear flow type. For this purpose, conventionally vibrated concretes (CVC), and self-compacting concretes (SCC) containing different volume fraction of aggregates are designed, and their rheological properties are investigated. The results indicate that the concrete pumpability, in terms of delivery rate for a given pressure, decreases by at least 30% for 10% increase in aggregates content by volume. The relative decrease in pumpability is more pronounced for CVC. Furthermore, it is shown that under certain experimental conditions the rheological properties of the lubricating layer (LL) can be approximated to those of the constitutive mortar in pumped concrete. Accordingly, the measurements on constitutive mortar can be used as a basis for the analytical prediction of pumping pressure. The obtained knowledge is a prerequisite for evaluating flow-induced particle migration (FIPM) during pumping and LL formation.

Shirin Fataei, Egor Secrieru, Viktor Mechtcherine
Effect of Mixing Procedure on the Rheological Properties and Hydration Kinetics of Portland Cement Paste

The mixing procedure used to make paste, mortar or concrete has an important influence on the hydration kinetics and rheological properties of cementitious materials. In this study, different shear mixing procedures were studied to evaluate the effect on the kinetics of hydration for Portland cement paste by isothermal calorimetry over 72 h. The rheological properties of the same pastes in terms of yield stress (Pa) and apparent viscosity (Pa.s) were also studied with the same mixing procedures: manual, 2500 rpm and high shear mixing at 10000 rpm. To compare the heat flow over the time of each mixing procedure with the stiffening, an oscillatory rheometry evaluation with continuous flow was carried out. All the tests were carried out in triplicate and the variability was evaluated.The results show important differences in terms of enhancement of height of the main heat evolution peak and reduction of the induction period when the paste was mixed at 10000 rpm (high shear), moreover, the oscillatory rheometry showed that the high shear mixing reduced the stiffening time of the mix compared to manual mixing and 2500 rpm mixing.

Danila Fabiane Ferraz, Ariane C. R. Martho, Elizabeth G. Burns, Roberto C. O. Romano, Rafael G. Pileggi
Development of SCC Placement Methodology for the Monolithic Construction of Slab-to-Wall Members Using Formwork Pressure and Time of Set-Based Modeling

This paper discusses the use of Self Consolidating Concrete (SCC) in a unique approach for the construction of combined slabs and wall members commonly encountered in modular construction in new nuclear facilities required to be cast monolithically. Use of vibrators or other tools for surface set determination was not feasible due to lack of access in the 20 m steel-composite module walls. In addition, a material “upwell” in the slab segments during the vertical rise of SCC in the steel-composite module wall was not desired and needed to be managed. Therefore, the rate of rise, time of set, and formwork pressure-related considerations needed to be properly managed for the apparently “fluid” SCC mixture in the combined slab-to-wall placement to prevent upwell and/or high formwork pressures while avoiding cold joint/bond issues. This paper discusses the unique engineering approach to the construction challenges and related testing performed to overcome these challenges and manage the engineering properties in a critical slab-to-wall placement. Engineering considerations and the field trials in preparation for a 71 h, monolithic 1415 m3 placement in critical areas in a new nuclear facility are discussed. Among the testing performed in preparation for the placement was the filling of 3 m, and 6 m tall mock-ups to measure formwork pressures at intended placement rates. Floor-to-wall mock-ups were performed consisting of an exposed horizontal section and a vertical section to observe upwell tendency as well as verify set or cold joint occurrence by subsequent saw cutting. Multiple time of set determination testing of the SCC mixture at different concrete temperatures were performed with the purpose of developing time of set curves to be used in the development of a placement plan.The engineering evaluation and input was particularly of value in the successful completion of the 1415 m3 placement lasting 71 h.

Boris Haranki, Ufuk Dilek
Influence of Segregation on Materials Component in Fresh Concrete Due to Vibration

Variations in the degree of deterioration of a concrete structure are caused by variations in concrete quality and environmental impacts. Moreover, variations in concrete quality are also influenced by the segregation of fresh concrete due to vibration and bleeding. Considering this background, the degree of segregation of fresh concrete and its factors caused by vibration were experimentally investigated. As a result, it is found that the gravel settled due to the vibration while compacting the fresh concrete, whereas the cement paste rose up. Moreover, the longer the vibration time, the larger the amounts of risen cement paste and settled gravel. In addition, it is concluded that the mortar apparent viscosity and the inter-gravel average distance influenced the segregation of fresh concrete due to vibration.

Kazuaki Nishimura, Yoshitaka Kato
Study of the Mixing Completion in Concrete Production by Means of an on-Board Sensor System

The second industrial revolution has been accompanied by the massive use of concrete. However, rejected loads or demolitions of new structures due to poor quality indicates that quality control still needs to be improved. Furthermore, with the advent of the third industrial revolution, the industry needs more advanced production systems; for example, high-tech implementation processes like 3D concrete printing will require continuous rheology control systems. In that respect, to answer today’s and tomorrow’s questions, Université Laval has initiated a research program using an on-board sensor system for ready-mix concrete production to monitor real-time concrete fresh properties.One research interest of the program lies in the study of the completion of mixing, a crucial step to obtain quality concrete: after loading the materials, the driver adjusts the water and admixtures introduced while mixing to obtain the desired consistency. This article aims to highlight the path taken to determine the completion of mixing based on the probe assessment.Recent tests focused on the measurement of homogeneity by monitoring the pressures exerted on the probe. To better understand what happens in the drum, this step has necessarily involved viewing and studying the behavior of the material during mixing. Moreover, tests brought to light distinctive patterns in the pressures detected by the probe which could be synonym of segregation. Also, methods based on artificial intelligence to anticipate the completion of mixing are already under analysis and appear extremely promising.Finally, the ambition is to develop an automatic adjustment program that would add water and admixtures through an automatic gate. Resources consumption could be decreased, thus reducing the economic and environmental impact of the concrete production while improving concrete quality.

Pierre Siccardi, Xavier Berger, Robin Jean, Marc Jolin, Benoît Bissonnette, Denis Beaupré
Pumping Process of High Strength Self-consolidating Concrete in the Construction of Skyscraper

Lots of skyscrapers are or will be built in China. High strength self-consolidating concrete is used to construct composite steel concrete pillars and shear walls of core tube. It is introduced how to prepare high strength self-consolidating concrete with local raw materials and the controlling index for the workability of fresh concrete pumped to different heights. The pumpability of fresh concrete was evaluated in laboratory and in-site using normal workability evaluation methods and Sliper, a newly developed instrument to estimate pumpability of fresh concrete. A simulating pumping process of high strength self-consolidating concrete was done to investigate its performance using an experimental pumpline circuit with the total length of 2300 m. C100 concrete was pumped one time to the height more than 1000 m and cast without vibration in Shenzhen, China. Super-highly pumping of C70 self-consolidating concrete is widely performed now in the construction projects of skyscraper in China.

Peiyu Yan, Jianguo Han, Mengyuan Li, Yu Liu

Additive Manufacturing and 3D-Printing

Hardened Properties of 3D Printable Ultra-High Performance Fiber-Reinforced Concrete for Digital Construction Applications

The current progress of 3D concrete printing technique is hampered by the limited range of printable concretes and reinforcing methods. To tackle both limitations, a 3D printable ultra-high performance fiber-reinforced concrete (UHPFRC) was developed in this study with using locally available materials for digital construction applications. The hardened properties of the developed 3D printable UHPFRC, including density, compressive strength and flexural strength were experimentally measured. The effect of testing directions on the compressive and flexural strengths of the 3D printed UHPFRC was also investigated. A conventionally mold-cast UHPFRC counterpart mix was also made for comparison purposes. The results showed that the compressive strength of the printed UHPFRC samples exhibited an anisotropic behavior, depending on the loading direction. However, the flexural strength of the printed UHPFRC samples was comparable in lateral and perpendicular directions. The results also showed that the density and compressive strength of the printed UHPFRC specimens were relatively lower than those of the mold-cast samples. However, the flexural strength of the printed UHPFRC specimens was higher than that of the mold-cast specimens.

Ravendran Arunothayan, Behzad Nematollahi, Shin Hau Bong, Ravi Ranade, Jay Sanjayan
Properties of 3D-Printable Ductile Fibre-Reinforced Geopolymer Composite for Digital Construction Applications

Two main limitations of extrusion-based 3D concrete printing process are the incorporation of conventional steel bars and the limited range of printable concretes. To tackle both limitations, this paper investigates feasibility of developing a 3D-printable ductile fibre-reinforced geopolymer composite (DFRGC) for digital construction applications. Instead of the conventional cement binder, a “just-add-water” geopolymer binder was used for production of the 3D-printable DFRGC, which considerably improves its sustainability performance and commercial viability in the construction industry. A series of experiments including bulk density, apparent porosity, compression, and flexural tests were conducted to characterize the mechanical properties of the 3D-printable DFRGC. The effect of number of printed layers on the mechanical properties of the 3D-printable DFRGC was also investigated. Further, dependency of the compressive strength of the printed sample on the testing direction was also evaluated. The developed 3D-printable DFRGC exhibited deflection-hardening behaviour in flexure with high modulus of rupture of up to 10.2 MPa and deflection capacity of up to 5.3 mm. Therefore, the feasibility of developing 3D-printable deflection-hardening ductile geopolymer composites was established. The results also showed that the compressive and flexural performances of the 3D-printed DFRGC specimens depended on the testing direction and number of printed layers.

Shin Hau Bong, Behzad Nematollahi, Ming Xia, Ali Nazari, Jay Sanjayan, Jinlong Pan
Rheology of 3D Printable Lightweight Foam Concrete Incorporating Nano-Silica

Lightweight foam concrete (LWFC) has relatively high workability, or low static and dynamic shear resistance in the fresh state. It is also sensitive to applied pressure. These limitations present challenges for 3D printing of LWFC, through its pumping and extrusion, and bearing pressure of subsequent layers. The associated risks of 3D printing LWFC is therefore twofold, altering the LWFC properties during the printing process, and insufficient buildability. Inclusion of appropriate nanoparticles, with high surface area to volume ratio, is proposed here to influence the microstructure of the cementitious composite in the fresh and hardened state, in order to increase the shear resistance, and limit the impact of the 3D printing process on its density. Nano-SiO2 (nS) particles with a diameter smaller than 30 nm and 99.5% purity are incorporated into LWFC at 2% and 3% by weight of cement. Rheometer results indicate increased shear resistance and thixotropic behavior. Conservative buildability prediction based on the thixotropic properties is validated by 3D printed nLWFC building height of a circular hollow column.

Seung Cho, Jacques Kruger, Algurnon van Rooyen, Stephan Zeranka, Gideon van Zijl
Study on the Influence of Accelerators on the Hydration of Portland Cement and Their Applicability in 3D Printing

As extrusion based additive manufacturing (AM) has the potential of becoming the largest evolution in the construction industry in the 21st century, the control of early cement hydration becomes more and more important. This study focuses on the control of the compressive strength development of a CEM I 52.5R via the addition of different dosages of K2CO3, Na2CO3, Ca(NO3)2 and Triethanolamine (TEA) which all act as accelerators in cement hydration. Further, the influence of the above-mentioned substances on the hydration products formed during the first 24 h of hydration and their applicability in extrusion-based 3D printing processes was examined. The initial and final setting time as well as the compressive strength after 1, 2, 7 and 28 d were tested. The formation of hydration products during the first 24 h was studied using continuous in-situ XRD and calorimetric measurements. The early compressive strength development of the accelerated cement was tested, using a newly developed measuring device, starting at 20 min after the initial hydration. It was shown, that by adding the above-mentioned accelerators the initial setting time and the compressive strength development of the cement paste can be precisely adapted to the printing process. It could further be shown that the used accelerators strongly influence the hydration processes of the cement pastes and the crystallinity of some hydration products.

Tobias Dorn, Tamino Hirsch, Dietmar Stephan
Predication of Strength-Based Failure in Extrusion-Based 3D Concrete Printing

Extrusion-based concrete 3D printing is an emerging construction technique to build the desired structure layer by layer without using any type of formwork. Hence, the printable concrete requires to achieve adequate strength to support the self-weight and subsequent layers in short period of time. This paper aims to identify the strength-based failure limits of 3D printing concrete through experimental and numerical procedure. The 3D Printing experiments were carried out to obtain the height of failure (i.e., number of printed layers before failure). The important rheological parameters of 3D printable concrete mixes were estimated experimentally and used in a numerical simulation as well as in theoretical equations to compare the results. The strength-based failure criterion for 3D printed object was developed and validated numerically using FLAC 3D (i.e., Fast Lagrangian Analysis of Continua). The time-dependent material behaviour was considered in the numerical analysis and the failure mode and the failure heights were modelled and compared with the experimental values. It was found that the experimental results and the numerical simulation results are comparable and the numerical simulation can be used as a reliable tool to decide the rheological parameters of 3D printing concrete for preventing the strength based failure.

Roshan I. Jayathilakage, Pathmanathan Rajeev, Jay Sanjayan
Quantifying Constructability Performance of 3D Concrete Printing via Rheology-Based Analytical Models

3D printing of concrete (3DPC) is a developing automation technology that can promote further industrialisation in the construction industry. 3DPC has complex rheological requirements, namely low material viscosity for ease of pumping but high viscosity for constructability. Greater emphasis is therefore placed on the rheology of cement-based composites used for 3DPC compared to conventional construction techniques. Thixotropic materials demonstrate the material performance required for 3DPC. This research presents the work of Kruger et al., who developed a bi-linear thixotropy model [1] specifically for 3DPC materials. This model demonstrates the degree of thixotropy of a material and the static yield shear stress evolution after it has been extruded. A buildability model [2] predicts the maximum number of filament/printing layers achievable, which is based on the bi-linear thixotropy model. Lastly, a rheology-based filament shape retention model [3] determines the maximum height of a filament layer where no plastic yielding at a material point will occur. The three aforementioned models are applied in this research in order to quantify the constructability of 3DPC by only conducting rheology tests and no mechanical tests. A circular hollow column is 3D printed that validates the models presented in this research. The buildability model predicted 52 filament layers whereas 54 layers were obtained experimentally before failure, yielding a conservative 3DPC construction height prediction of 3.7%.

Jacques Kruger, Stephan Zeranka, Gideon van Zijl
Extrusion of Lightweight Concrete: Rheological Investigations

Lightweight concrete enables the production of monolithic exterior wall components with sufficient thermal insulation even under Central European climatic conditions. If, in addition, additive manufacturing by extrusion is used for production, these components can be further improved by installing air chambers to increase thermal insulation of the component or varying wall thicknesses to reduce material demand. Furthermore, it is beneficial to use lightweight aggregate concrete (LAC) instead of e.g. aerated concrete due to its higher robustness with regard to the pumping process. However, LAC differs from normal concrete as the porous lightweight aggregates absorb water and thereby change the characteristics of the fresh mixture. This applies in particular if the concrete is put under pressure during production, e.g. during pumping. This paper focusses on the effect of rheological parameters (especially plastic viscosity) on the pumpability of LAC. We found for the tested mixtures, pumped with an eccentric screw mortar pump, that pumpability was independent of the yield stress. Plastic viscosity, on the other hand, had a decisive effect on the pumpability of the LAC. By varying the total water to binder ratio, we found a significant effect on the pumpability, which is in line with the effect of the plastic viscosity. Furthermore, alternative concrete additives can affect the flow in the pipe, as is known from normal concrete. Our experiments show that limestone powder influences the pumpability independently of plastic viscosity and yield stress. With our results, we contribute to the development of a lightweight, 3D printable concrete.

Carla Matthäus, Daniel Weger, Thomas Kränkel, Luis Santos Carvalho, Christoph Gehlen
Enhancing Strength of Powder-Based 3D Printed Geopolymers for Digital Construction Applications

The authors of this study have recently succeeded to formulate geopolymer as a printing material to be used in commercially available powder-based 3D printers for the manufacture of ‘free-form’ components with complex geometries without the use of expensive formwork. This study focusses on post-processing methods to increase the strength of powder-based 3D printed geopolymers. The effects of curing medium, curing temperature, curing time and loading direction on the compressive strength of the printed geopolymers were investigated. The printed samples were cured in two different sodium (Na)-based and potassium (K)-based alkaline solutions at two different curing temperatures (ambient-temperature (23 °C) and 60 °C) for 7 days and 28 days. The compressive strength of the post-processed geopolymer samples was measured in two different loading directions. The results showed that the post-processed printed geopolymer specimens cured in the Na-based solution exhibited higher compressive strength than that of the specimens cured in the K-based solution. This is true regardless of the curing temperature, curing time and loading direction. In addition, the 28-day compressive strength of the ambient-temperature-cured post-processed printed geopolymer samples was comparable to the 7-day compressive strength of the heat-cured samples. This is true regardless of the curing medium and loading direction.

Behzad Nematollahi, Ming Xia, Jay Sanjayan
Rheology and Structural Rebuilding of One-Part Geopolymer Mortar in the Context of 3D Concrete Printing

The employment of automation in construction has not yet reached its full potential. 3D concrete printing is one of the promising construction techniques which has drawn a lot of attention due to its unique benefit in terms of higher productivity, faster construction processes, geometrical freedom, and cost-efficiency. With the number of 3D printing projects increasing rapidly, the demand for accurate measurement of concrete fresh property is also increasing. Therefore, in this paper rheology and structural rebuilding properties are investigated to understand printability and buildability attributes of one-part geopolymer mixtures. A custom made geopolymer binder was designed for extrusion-based 3D printing and the fresh geopolymer was tested in different resting time to reveal the structural rebuilding property via measurement of compressive green strength. The material test result shows that the green strength increases with fresh concrete age, as does the static yield strength.

Biranchi Panda, Nisar Ahamed Noor Mohamed, Ming Jen Tan
Rheology of Fresh Concrete: Historical Perspective and Glance in the Future

Conventional casting and placement of concrete involves fragmented tasks such as reinforcement arrangements, formwork assembling and dismantling later, and concrete pouring. Recent study on the automation in construction reports that the fragmented construction can be possibly replaced by continuous operations such as 3D printing. The use of continuous operations can reduce the time of construction and consequently construction expenses. Control of the rheology of fresh cement-based materials is the key technology to realize the continuous casting of cement-based materials. Various precursors of 3D printing are summarized, and basic understanding toward the continuous casting is provided in terms of the rheology.

Surendra P. Shah, Jae Hong Kim
Processing of Set on Demand Solutions for Digital Fabrication in Architecture

Digital fabrication with concrete holds potential to rationalize the production of large-scale mass-customized shapes in architecture. However, these digital technologies have manifold requirements for concrete compared to ordinary casting due to the relatively long production time combined with the need for fast strength build-up after placing. Thus, first, a large retarded batch of concrete is prepared to provide extended open time for fabrication. Then, the retarded concrete is accelerated on demand in small increments over the course of the experiment.This paper discusses suitable set on demand compositions to increase the buildability of three specific processes, Smart Dynamic Casting (SDC), Digital Casting (DC) and layered extrusion as they have similar requirements for concrete during fabrication. SDC and DC need low yield stress upon acceleration for casting and all three of them require consistent, rapid strength evolution for building.Two significantly different material compositions, a SCM and an UHPFRC are studied using two formulated accelerators. The overall hydration and strength build-up kinetics are investigated with calorimetry, slow penetration and uniaxial compression measurements. It was found that the rate of yield stress evolution can be customized with both mortars by using different dosages of accelerator and that the onset of strength build-up depends on the type of mortar formulation. The proposed acceleration method is a promising approach to increase the fabrication speed and the possible building height for a given mix design in applications like SDC, DC or layered extrusion.

Anna Szabo, Lex Reiter, Ena Lloret-Fritschi, Fabio Gramazio, Matthias Kohler, Robert J. Flatt
Residence Time Distributions in Continuous Processing of Concrete

Digital fabrication with concrete introduces new challenges in terms of continuous processing of concrete. To enable increased vertical building rates, accelerators are dosed at a nozzle reactor unit directly before placement in many of these processes. The details of this mixing process have large implications for the behavior of the system and the success of the process. The measurement of residence time distribution (RTD) is a potentially useful tool in understanding these processes and diagnosing pathological behavior of reactors. In this study, the RTD of the Smart Dynamic Casting (SDC) reactor is measured, and implications for this process and other digital fabrication processes are considered.

Timothy Wangler, Fabio Scotto, Ena Lloret-Fritschi, Robert J. Flatt
Post-processing Techniques to Enhance Strength of Portland Cement Mortar Digitally Fabricated Using Powder-Based 3D Printing Process

The authors of this study have recently succeeded to formulate a Portland cement-based mortar as a printing material for use in commercially available powder-based 3D printers to build ‘free-form’ concrete components with complex geometries for construction applications. This study focusses on post-processing methods to enhance the strength of cement mortar specimens digitally fabricated using the powder-based 3D printing technique. The effects of type of curing medium (tap-water vs. saturated-limewater), curing time (7 days vs. 28 days), and loading direction (binder-jetting direction vs. layer-stacking direction) on the compressive strength of the printed samples were investigated. The results showed that the compressive strength of the printed samples cured in either tap-water or saturated-limewater was significantly higher than that of the ‘green’ samples. However, the 7-day and 28-day compressive strengths of the saturated-limewater-cured samples were 26% and 17%, respectively higher than those of the corresponding tap-water-cured samples. The results also showed that the compressive strength of the 3D printed cement mortar specimens depended on the loading direction. However, the degree of anisotropy in the compressive strength was reduced with the increase of curing time.

Ming Xia, Behzad Nematollahi, Jay Sanjayan

Rheology and Workability of SCC

Rheology Study of Fresh Self-compacting Concrete Made Using Recycled Fine Aggregates

The paper herein presents the results of an experimental work carried out to investigate the rheological behaviour of self-compacting concrete (SCC) mixes, which were produced by replacing natural sand with recycled fine aggregate (RFA) and using supplementary cementitious materials. A cross-vane rotating type rheometer has been used to evaluate the rheological parameters of the mixes. A total of 5 different SCC mixes having varying RFA content (0%, 50% and 100%) and binder composition (30% fly ash with 10% silica fume and 40% fly ash without silica fume) have been investigated. The results showed that the yield stress of the SCCs increased with increase in the RFA content in the mixes, and it reduced when fly ash content was increased keeping RFA content constant. The mixes with 100% RFA content resulted in very high shear stress and it increases at higher rate with respect to time. Bingham parameters were obtained and linear correlation with high correlation coefficient value were found, which confirmed that the fresh self-compacting concrete having RFA can be properly modelled as a Bingham fluid. The thixotropy of the SCCs was evaluated in terms of breakdown area and drop in apparent viscosity. A strong correlation is found between breakdown area and drop in apparent viscosity at vane rotation speed from 0.1 rps to 0.4 rps.

Monalisa Behera, Ashwani K. Minocha, Sriman K. Bhattacharyya, Mohammad R. Rahman
Experimental Study of Formwork Tightness as a Function of Rheological Properties of SCC

Several studies relating formwork pressure to rheology exist, however the relationship between rheology and leakage through formwork joints remains to be investigated. In practice, standard documents are used to define formwork tightness requirements, typically using a qualitative approach. To try bridge this gap in knowledge, we developed a test set-up to study tightness of formwork joints under pressure as a function of varying rheological properties. Coupled with standard rheology tests, this new test set-up provides means of linking flow rate, formwork pressure, flow area, and the rheological properties. The study seeks to provide insight on measurable governing parameters and thus inform formwork tightness requirements in a more quantifiable manner.This paper presents a test set-up designed to study the flow of fresh paste through small openings. It highlights a preliminary study on the pressure-driven flow of limestone paste through a bottom orifice in a cylindrical container. While this new device may not be directly representative of the actual conditions in formwork, it provides a good base for a fundamental study that can then be extrapolated to a more representative test operation. Preliminary results show a linear relationship between the flow rate and the applied pressure. The results also show that increasing the flow area by a factor of 2.33 had a higher impact than an increase in yield stress and viscosity by a factor of 2.54 and 3.80 respectively. However, more tests need to be carried out to obtain clear trends.

Chizya Chibulu, Khadija El Cheikh, Mert Y. Yardimci, Geert De Schutter
The Effect of Fiber Geometry and Concentration on the Flow Properties of UHPC

The economic relevance of fiber-reinforced concrete has increased steadily throughout the years. Fiber reinforcement improves the mechanical properties of concrete structures, but at the same time has the disadvantage of worsening the workability of fresh concrete. In order to better understand the influence of the fibers on the fresh concrete properties, rheological measurements were carried out on suspensions with fibers of typical rod-shape and atypical ring-shape with volume fractions up to 3.3% and 4.8% respectively. The study is carried out on UHPC as a matrix fluid as well as on a silicone oil as a substitute fluid with comparable flow properties. Investigation on a substitute fluid has the advantage of excluding interferences caused by thixotropy and interaction with granular components.The measurements were carried out with ball probe systems and evaluated with a numerical simulation-based procedure in such a way that objective physical Bingham material parameters could be determined. It was found that due to the weak interaction of the fibers, the increase in viscosity with the fiber volume fraction is linear and independent of the fiber geometry. For the same reason, no significant yield stress has been detected.

Florian Gerland, Maximilian Schleiting, Thomas Schomberg, Olaf Wünsch, Alexander Wetzel, Bernhard Middendorf
Rheological Characterization of Self-compacting Concrete Pastes with Polymeric Admixtures

Multipurpose admixtures such as superplasticizers (SP), viscosity modifying agents (VMA) and superabsorbent polymers (SAP) are polymers commonly used in self-compacting concrete (SCC). Their main effect is positive for SCC fresh properties, minimizing some technical barriers of SCC production and cast in-place technology. However, they also affect fresh SCC rheological properties. This study addresses the rheological behaviour of fluid SCC pastes, modified with SP, VMA, SAP and their combined effects and interactions. A cement-limestone filler blended paste and two water-to-binder ratio (w/b) were designed as a reference mixture. Three dosages of VMA and SAP, 0.2%, 0.4% and 1.0% of cement weight, were investigated. The kinetics of water uptake of VMA and SAP admixtures were compared using the tea bag test in neutral pH and alkaline pH solutions. Additionally, SP was added to achieve a similar slump flow with final spread diameters of 300 mm and 400 mm, on pastes with and without VMA and SAP. The rheological parameters of the fresh pastes were tested with the mini-cone slump test. Final spread diameter, final height and time to final spread were measured after the mixing. It was found that the effectiveness of SP on the final spread diameter depended on the w/b ratio of reference paste. On the other hand, VMA increased the time to final spread, while slightly reducing the final spread diameter. SAP affected the maximum diameter due to water absorption kinetics and an increase of w/b ratio was needed to achieve similar spread diameters. It was observed that the combined use of SP and VMA or SAP affected the measured parameters. The particular effects of SP, VMA and SAP admixtures on the rheological parameters depended on w/b ratio, the amount of polymer and the combination of components.

Irene Palomar, Gonzalo Barluenga, Cynthia Guardia, Ma Cruz Alonso, Marina Álvarez
Effect of Limestone Powder Addition Quality on SCC Rheology

Limestone powder is increasingly used as a supplementary cementitious composites in order to reduce the environmental impact of concrete. Limestone powder can simultaneously improve the rheological behaviour of the paste, increases the solid volume fraction and reduces the shrinkage of the concrete. The quality of limestone fillers is quarry-dependent and varies with the mineralogy of the original limestone rock. The filler produced can thus contain small but significant amount of different kinds of impurities.In this study, the change in SCC rheology (yield stress value) induced by the variation in quality of the limestone filler (coming from the same quarry) is analysed.In a first part, mineralogical analyses are performed in order to identify the nature of chemical species present in the limestone filler in addition to calcite. Then, the effect of calcite content in the limestone filler on the yield stress of limestone suspension is investigated using conventional rheometry.The results highlight the presence of a critical content of impurities above which the yield stress of the limestone filler shows a dramatic increase. This high value of the yield stress implies a complete redefinition of the SCC mix-design.Finally, a simple rheological test, based on cone penetration test, is proposed in order to quickly evaluate the quality of the filler before its introduction into the production process. This test can be used as a quality control procedure in order to define whether there is a need to change the mix design of SCC.

Damien Rangeard, Arnaud Perrot, Malalasoa Rodomond
Rheological and Mechanical Properties of Alkali-Activated Hybrid Matrix for Self-consolidating Concrete

The objective of this study is to evaluate the flow behavior, build-up kinetics, and mechanical properties of an alkali-activated hybrid matrix using different concentrations of NaOH. The investigated mixtures showed different rheological behaviors depending on the NaOH concentration. The combination of Portland cement and fly ash contributed to the formation of a rigid network when the activator is used at a concentration of 2 mol/L. At this low concentration, the chemical reaction seems to be strongly accelerated. This resulted in an increase in the yield stress, plastic viscosity, and rigidification rate of the mixtures. However, when the concentration of NaOH increased to 14 mol/L, only cement contributed to the development of rigidity, and fly ash did not show any contribution. This resulted in relatively low yield stress, plastic viscosity, and rigidification rate. Moreover, the obtained test results revealed that the compressive strength of mortar mixtures made with cement - fly ash hybrid matrix is higher than that of fly ash-based mortar mixtures.

Yasser Rifaai, Ammar Yahia, Ahmed Mostafa, Salima Aggoun, El-Hadj Kadri
Effects of Nanoclays on SCC Paste Rheology

Self-compacting concrete is an efficient and advantageous technology that increases cast in place speed while reduces energy consumption and health risks. However, some difficulties regarding pumping and lateral pressure on the formwork still limits its widespread use. A promising alternative for reducing the formwork pressure is the use of nanocomponents. Among them, nanoclays such as sepiolite, attapulgite, and montmorillonite can modify the rheological properties of fresh concrete, increasing early age thixotropy and structural build-up. These nanoclays have different morphology and nature, but similar size or BET surface area. In order to evaluate the effect of nanoclays on early rheology of SCC pastes, an experimental study was carried out. A reference paste with ordinary Portland cement blended with limestone filler, 3:1 by weight, was designed and two water-to binder ratios (w/b), 0.35 and 0.45, were considered. Then, four types of nanoclays were incorporated: attapulgite, montmorillonite and two types of sepiolite, one in powder form and the other dispersed in water. Water adsorption was tested using the tea-bag method in tap water and alkaline pore water. Paste consistency was measured by slump flow adjusted using a high range water reducing admixture (HRWRA). The rheological behaviour of the mixtures was tested using the mini-slump flow test. The final spread diameter and time to final spread after mixing were assessed. The aim of this study is to understand and evaluate the effect of nanoclays on the rheological parameters of pastes with cement and limestone filler, which may improve the rheology and the structural build-up at rest, overcoming the problems identified for SCC.

Hugo Varela, Gonzalo Barluenga, Irene Palomar, Alberto Sepulcre

Mechanical Properties, Durability and Sustainability of SCC

Revised Macro-cracking Criterion for Massive Non-reinforced Self-compacting Concrete Structures Under Thermal Load Based on Extensive Experimental Testing and Field Observations

The Supercontainer is a reference concept of the Belgian Agency for Radioactive Waste and Enriched Fissile Materials (ONDRAF/NIRAS) for the post-packaging of vitrified high-level waste and spent fuel destined for deep geological disposal. The behaviour of this massive concrete structure was studied using macro-scale modelling, based on extensive experimental testing at lab-scale and validated by means of an experimental program, using realistic scale models. One of the objectives of this study was to predict and overcome possible cracking of the different cementitious layers in the container.The experimental program used half-scale models of the Supercontainer constructed in two main phases: (i) the construction of a non-reinforced concrete buffer with an inner cavity using a self-compacting concrete mixture, and (ii) the embedment of a heat-emitting source in the cavity of the buffer to simulate the heat-emitting conditions of a real overpack. This paper provides a brief discussion of the test setup used in the experimental program as well as the instrumentation, concrete mixing and the casting process during the two construction phases of the experiment. The macro-cracking criterion used to predict cracking onset and evolution in the cementitious layers is critically reviewed by comparing the simulated tangential and axial stresses in the axi-symmetrical container with in-situ experimental measurements.

Bart Craeye, Lou Areias, Maarten Van Geet, Saeid Babaei
Experimental Investigation on Mechanical Properties of Fiber Reinforced Lightweight Self-consolidating Concrete

This paper presents the results of an experimental investigation on the mechanical property of different types of fiber reinforced lightweight self-consolidating concrete (FRLWSCC) with three different types of fiber: High-Density Poly Ethylene (HDPE), Crumb Rubber (CR) and Polyvinyl Alcohol (PVA). Three developed mixes were compared in terms of compressive strength, flexural strength, stress-strain development, splitting tensile capacity, ductility, energy absorption capacity and stiffness with the lightweight self-consolidating concrete (LWSCC) without any fiber. For each category of tests, 20 samples were produced and tested. The results of the performed tests showed that the addition of fibers reduced compressive strength. In case of lightweight mixes with HDPE and PVA fibers, the reduction of compressive strength was more than 15%. However, all the fibers increased the flexural strength capacity with higher deflection at failure, meanwhile all type of fibers increased the number of cracks and reduced crack width at failure stage. Additionally, the splitting tensile capacities of FRLWSCC mixes were higher than LWSCC without fiber. All the FRLWSCCs showed a higher ability to absorb more energy. All FRLWSCC samples had a higher ductility capacity and exhibited a relatively lower stiffness.

Ali Ehsani Yeganeh, Farzad Kouroshnezhad, Sina Dadsetan, Khandaker M. A. Hossain, Mohamed Lachemi
Utilization of Copper Slag in Self-compacting Concrete - Strength and Permeation Properties

The aim of this research was to prepare and evaluate the properties of self-compacting concrete mixes by replacing fine aggregates with copper slag. Copper slag is an industrial by-product of copper manufacturing industry. Various concrete mixes with constant water to- binder (w/b) ratio of 0.42 were produced, and the replacement level of fine aggregates by 0%, 20%, 40% and 60% copper slag were utilized for the purpose of evaluating the performance of SCC. The mechanical and the chloride migration property of the self-compacting concrete mixes were determined after 28 days of standard curing period. The fresh properties of SCC mixes were also studied. Results indicated that the properties of self-compacting concrete could be highly enhanced incorporating copper slag but in selective percentage of fine aggregate.

Nikita Gupta, Rafat Siddique
Characterization of Non-proprietary UHPC for Use in Rehabilitation/Strengthening Applications

UHPFRC has become one of the most promising cement-based materials for the next generation of infrastructures because of its good workability, outstanding mechanical properties, and excellent durability. A promising field of application is the rehabilitation and/or strengthening of existing reinforced concrete structures, in which a new layer of UHPFRC replaces the deteriorated concrete (cracked, carbonated, chloride attack, etc.). The combination of the UHPFRC as protective layer, which can be reinforced, provides a simple and efficient way of increasing the durability (extending the service life), the stiffness and structural resistance capacity while keeping compact cross sections. A study was carried out to test a non-proprietary UHPC mix containing equilibrium catalyst to determine whether this new mix is a viable option for rehabilitation/strengthening applications. Several mechanical properties and durability were assessed, such as early age E-modulus development and autogenous shrinkage, compressive strength evolution in time, uniaxial tensile strength, water absorption by capillarity, chloride ion penetration, alkali-silica reactivity and sulphates attack resistance. Test results show that new UHPC developed present equivalent performance to other UHPCs cured under normal curing conditions.

Ana Mafalda Matos, Sandra Nunes, Carla Costa, José L. Barroso-Aguiar
The Applicability of Reclaimed Concrete Granulate to SCC

Reclaimed aggregate granulate production is one of the most promising methods of utilization of unused fresh concrete. Its main advantage, as compared to other technologies, is the 100% reusability of the base material. Here, 2-component admixture technology was chosen. According to its producer, its usability is restricted to an S4 consistence maximum. The authors’ intention was to perform a preliminary investigation to check whether it is possible to broaden this limit to SCC. It is an important task, as, time to time, it occurs that a delivery of SCC has to be rejected on-site. During this study fresh SCC was tested as well as compressive strength development (up to 90 days) and splitting tensile strength was checked after 28 days of hardening. Two SCC compositions were tested: one similar to low-cement content Eco-SCC and the second, similar to a typical binder-rich SCC. The granulate composition was obtained by thinning SCC of intermediate composition with dry aggregate to the level which enables the maintenance of an original aggregate grading curve after granulate hardening. Next, for simplicity, the granulate for the main research programme was produced from traditional concrete of S1 consistence, based on the same aggregate composition as SCC and the same paste content as in the thinned SCC. Two moisture content levels were tested: natural and wetted to the maximum water absorbability level of the coarse granulate. The results showed that it was possible to obtain well-workable SCC containing up to 15%–30% replacement by the natural state granulate, and up to 45% replacement using the wetted one. All granulate containing SCCs had the strength development not worsened in comparison to the base compositions.

Maciej Urban, Małgorzata Lenart

Modelling and Numerical Simulations of Rheological Behaviour

Particle Interactions in Silica Systems in Presence of Superplasticizer

The flowability of cement paste is of great importance in today’s construction industry and is influenced by additives such as superplasticizers (SP). One type of SPs are polycarboxylate ether type SPs. These additives electrostatically bind with the negatively charged carboxylic groups at the backbone to the positively charged clinker phases. To model positively charged clinker phases with adsorbed SP, silicon wafers are pre-coated with cationic polyethylenimine (PEI) and SP is adsorbed onto the coated surface (Si/PEI/SP). Two different polycarboxylate ether type (PCE) SP are compared – one for ready-mix concrete and one for precast concrete. In this preliminary study the interaction forces between Si/PEI/SP surface and a silica microsphere (colloidal probe) are investigated under mild physico-chemical conditions (pH ~6, ion concentration <10−5 M) using Colloidal Probe Atomic Force Microscopy (CP-AFM).The interaction force between the model surfaces is attractive for low concentration of SP. The force changes from attractive to repulsive by increasing amount of SP. The force upon approach reveals a biexponential behavior. The exponential decay at large and short surface separations are attributed to electrostatic and steric interactions, respectively. The steric forces of the SP for ready-mix concrete show a steeper onset than the SP for precast concrete.The quantification of these interaction forces will be compared to rheological measurements of similar systems. Furthermore, the parameters will be changed to better approach the conditions in real systems, i.e. higher pH and ionic strength. This helps to understand how the forces on the nanoscale influence the macroscopic rheology.

Simon Becker, Zichen Lu, Sarah Leinitz, Wolfram Schmidt, Dietmar Stephan, Regine von Klitzing
Fresh Concrete Pumping Arrest Investigation for Thixotropy by a CFD Modelling Approach

Concrete pumping operations determine construction speed, finishing quality, durability and even structural integrity. When pumping operations cannot be continued, most problems occur due to complex time-dependent transformations. This causes significant industrial costs (e.g. material and delay). Since time-dependent aspects are currently not fully understood and cannot be predicted, a way to quantify time-dependent aspects is needed. Therefore, we make an attempt by numerical simulation by comparing thixotropic cases with different pumping arresting times. After an introduction to fresh concrete rheology and numerical modelling, ten representative thixotropy cases are analysed. Despite some unresolved numerical instabilities, the numerical framework allows to estimate pumping pressure peaks after resting time. The results evaluate a thixotropy model, which is generally applicable for less thixotropic SCC’s. It is clear that flow re-initiation after rest in concrete pumping is poorly understood. Numerical simulation could be one approach for further analysis and is potentially important for practice. Future work such as simulation of concrete mixers, pressure increase after pumping arrest, formwork pressure decay and leakage are therefore recommended.

Robin De Schryver, Khadija El Cheikh, Mert Y. Yardimci, Karel Lesage, Geert De Schutter
Numerical Simulation of the Flow Behavior of Newtonian Fluids in a Wide Gap Rheometer by CFD

Wide gap coaxial rheometers with vane-in-cup systems are widely used to determine rheological properties of cement paste, mortar and concrete. Available analytical models allow the calculation of average shear stress with acceptable accuracy. However, they exhibit serious oversimplifications, e.g. torque contributions of other parts than the vertical cylinder equivalent surface or neglecting of stress peaks. Hence, the accuracy of calculated shear stress values may be questionable depending on the actual purpose. In the present contribution, experimental investigations of Newtonian fluids in a wide gap rheometer with both, a coaxial smooth steel cylinders and a vane-in-cup system, are presented. Accuracy of analytical models is discussed with respect to shear rate distributions over gap and over cylinder resp. vane probe surfaces determined from Computational Fluid Dynamics (CFD) simulations. A modified analytical model is proposed. As will be shown, the averaged shear rates over one revolution calculated from CFD simulations are comparable with the modified analytical model. Further results are discussed and an outlook for future research is given.

Mahmoud Eslami Pirharati, Dimitri Ivanov, Hans-W. Krauss, Carsten Schilde, Dirk Lowke
Segregation of Granular Material During the Transport in Pipes

Concrete is a material known for its complex rheology and segregation behavior. Especially near the wall, a zone depleted of coarse aggregates is found – the lubrication layer. The mechanism for the formation of the lubrication layer depends on hydrodynamic effects as well as on the particle/particle interactions. An apparatus for the optical investigation of coarse glass particles dispersed in Newtonian and non-Newtonian model liquids was designed to observe the migration. Due to a pneumatic pumping of the suspension, the flow regime can be varied from constant to pulsating. Besides to measurements of the pressure loss during the pumping, the measurement area is optically accessible. The flow in the tube is measured by particle image velocimetry (PIV) and particle tracking velocimetry (PTV). With these techniques it is possible to visualize the velocity field in the near wall region and to track the position of particles.The results of these measurements should be part of a benchmarking process of numerical simulations. Based on measurements and corresponding numerical simulations, we want to develop a rheological description of the lubrication layer near to the pipe wall.

Martin A. Haustein, Rüdiger Schwarze
Synthesis and Analysis of Spherical Cementitious Model Particles

A new model system of spray dried particles was developed for the characterization of cementitious materials by Colloidal Probe Atomic Force Microscopy (CP-AFM). Prior to the current work it was not feasible to use CP-AFM with cementitious materials due to their inhomogeneous nature and non-sphericity. With the help of spray drying, it is possible to produce spherical and homogeneous particles with different roughness. Ordinary Portland Cement (OPC) is the examined material in this work.The model particles are produced in multiple steps. First, the original OPC particles are sieved and nano-ground in ethanol using a planetary ball-mill. After spray drying the cementitious nanosuspension, the chemical composition of the model particles’ surface as well as the bulk chemical composition are determined using X-ray Photoelectron Spectroscopy (XPS) and X-ray fluorescence measurements (XRF). Furthermore, the shape, size and roughness of the spray dried particles are estimated by Scanning Electron Microscopy (SEM) and laser diffraction analysis. Finally, first CP-AFM measurements are performed to access the interaction forces between the model particles in ethanol.The experimental results show that the median primary particle sizes produced by nano-grinding are below 200 nm while the diameter of the spray dried particles are in the range of 10 µm. Furthermore, the results show that particles produced from OPC seem to have a lower content in calcium oxide (CaO) at the surface regions compared to the bulk cement. Possible reasons for these findings are discussed.

Dimitri Ivanov, Simon Becker, Zichen Lu, Mahmoud Eslami Pirharati, Arno Kwade, Hans-W. Krauss, Dietmar Stephan, Regine von Klitzing, Carsten Schilde
Comparison of Water-Isopropanol Replacement and Lyophilisation for Hydration Stop of Cementitious Suspensions

For modern concrete technology, rheology is crucial for characterizing the properties of fresh concrete on the basis of physically defined parameters. These properties can be influenced by many factors, but have an effect on paste level predominantly. To obtain an understanding of influencing factors such as the underlying kinetics and mechanisms at the initial colloidal scale a time variant analysis of cementitious suspensions is needed. In this article, a method to stop the hydration process of cementitious suspensions at any time by gradual water-isopropanol replacement and lyophilisation is demonstrated. Therefore, three different methods for hydration stop are investigated, namely water-isopropanol exchange, lyophilisation as well as a combination of both, and compared to pristine (non-reacted) cement particles. Analysis of dried samples leads to the observation that direct lyophilisation leads to particles of similar size as the pristine cement particles. Water-isopropanol replacement as well as water-isopropanol exchange with subsequent lyophilisation, instead, leads to a very broad particle size distribution with larger particles, which might be attributed to secondary agglomerations of particles. We further investigate the three different hydration stop methods by evaluating the pore size distribution by means of nitrogen physisorption. Additionally, scanning electron microscopy (SEM) as an imaging method is used.

Patrick A. Kißling, Dario Cotardo, Tabea von Bronk, Ludger Lohaus, Nadja C. Bigall
Rheological Properties of Silica Beads in the Presence of Different Polymers and Electrolyte

Properties of interstitial liquid phase in cement paste, including the species and concentrations of polymers and ion etc., play an important role for the rheological properties of cementitious materials. In order to better understand their effect, an inert model substance, spherical silica beads (SBs) with defined surface and granulometry were used in the presence of electrolytes (CaCl2) and/or different polymers, including polycarboxylate superplasticizer (PCE) and polyethylene glycol (PEG). It was found the presence of Ca2+ greatly increases the viscosity and yield stress of silica beads paste (SBP), which is proportional to the [Ca2+]. For the effect of PCE, the addition of PCE is beneficial to the flowability of SBP, but a high dosage of PCE leads to a reversal effect. Furthermore, the yield stress firstly increases and then decreases with increasing [Ca2+] under the same dosage of PCE. The addition of PEG always increases the yield stress of SBP, regardless of the ion concentration and the presence or not of PCE.

Zichen Lu, Simon Becker, Sarah Leinitz, Regine von Klitzing, Wolfram Schmidt, Dietmar Stephan
A Plasticity Theory Approach for the Stability Analysis of Vertical Layers of Concrete in the Fresh State

The industrial production of cement is currently responsible for around 5% of global CO2 emissions. Hence, the development of technologies aimed at minimizing the use of cement in concrete structures, while preserving their strength and durability properties, plays a vital role in the reduction of carbon emissions. The use of cement in concrete structures can be minimized through the manufacture of functionally layered structural elements where concrete with high cement content is used rationally only when it contributes significantly to the performance of the structure. In functionally layered concrete, horizontal variation in material composition can be achieved by casting adjacent vertical layers of different materials. Removable vertical panels can be used to demarcate the mixes during casting. A good bond between the layers can be achieved by removing the panels prior to concrete hardening. However, a major problem with this application is the control of the fresh-state deformations of the adjacent vertical layers. This study investigates the fundamental problem of fresh state stability of concrete prisms that consist of two vertical layers of different mixes. A novel limit-state approach based on plasticity theory is formulated to assess the stability of the system as a function of material properties and geometry. The relationship between material parameters, system stability and geometry is determined and the formulated limit-state approach is validated against experimental results.

Giacomo Torelli, Janet M. Lees
Hydrating Cement Particle Interaction Model for Yield Stress Analysis

This study overviews existing methods for analyzing cement paste yield stress, and presents a new approach based on micro-structural computation. The proposed model explicitly considers cement particle interactions, both the colloidal and the nucleated gel ones. A new algorithm is proposed based on flocculating of poly-dispersed hard spheres in a simulation box, followed by nucleation of mono-sized nano-gel particles. The obtained virtual microstructures are than used as an input for a mechanical approach, which is conceptualized for simulating sliding kinematics needed to initiate the flow of the percolated solid network, i.e. to reach the paste yield stress. The microstructural modeling tool provides insights on how the localized gel is bridging the cement particles, responsible for the yield stress properties of bulk cement paste. Thus, it provides a promising new approach for quantifying the evolution of the bridging strength with nucleation (shear rest) time, enabling parametrization of the mechanical yield stress computation at micro-structural scale.

Neven Ukrainczyk, Antonio Caggiano, Diego Said Schicchi, Albrecht Gilka-Bötzow, Eddie Koenders
Measuring Thixotropic Properties in a Truck Mixer - Analysis by Numerical Simulation Using the PFI Material Model

Currently, 3D printing is getting an increasing attention as it can offer new advantages over the traditional construction methods. However, to be functional as a “printing-material”, the applied cement based material must possess a certain degree of thixotropic behavior. To speed up quality control at job site, it is relevant to investigate the possibility of using the truck mixer to measure such properties. This is the topic of the current paper, done by using computational fluid dynamics (CFD). With this, the overall test environment is thoroughly controlled and the experimental error is avoided, thus allowing the truck’s true potential to be examined.

Jon Elvar Wallevik
Computational Segregation Analysis During Casting of SCC

Uneven aggregate distribution can increase the local porosity and thus the permeability of concrete. Varying content of mortar causes heterogeneous shrinkage and creep in a given element. Moreover, high heterogeneity will increase the probability that these phenomena yield high internal stress gradients and thus cracking. In this work, a status is given about the development of a concrete casting solver within the OpenFOAM framework that can calculate the coarse aggregate distribution as a function of time. The aim is to predict the effect of segregation by gravity as well as by the shear rate induced particle migration. Case examples show that the latter can play a very important role in affecting the aggregate variation within a concrete element.

Jon Elvar Wallevik, Wassim Mansour, Olafur Haralds Wallevik
Rheology and Processing of Construction Materials
Prof. Viktor Mechtcherine
Prof. Dr. Kamal Khayat
Egor Secrieru
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