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See detailOvercome of bed-joint imperfections and improvement of actual contact in dry-stacked masonry
Chewe Ngapeya, Gelen Gael UL; Waldmann, Danièle UL

in Construction and Building Materials (in press)

Several researchers studied dry-stacked masonry walls (DSM) and inferred that the actual contact surface between the different block rows and the compressive strength in such walls are reduced by bed ... [more ▼]

Several researchers studied dry-stacked masonry walls (DSM) and inferred that the actual contact surface between the different block rows and the compressive strength in such walls are reduced by bed-joint imperfections as well as by height differences between different masonry blocks leading both to high stress concentration. This paper concentrates on the first type on imperfections. Through experimental tests, it analyses the influence of bed-joint roughness on the load bearing capacity and investigates a strategy to improve the load-bearing capacity of DSM by placing an additional horizontal layer on the top face of raw masonry blocks. First, different contact layers using conventional and auxetic materials were applied. Then 20 dry-stacked masonry prisms built with raw and improved masonry blocks were tested under axial compressive load until failure. Prescale Fujifilm strips were used to measure the actual contact in the bed-joints. Experimental tests show that the use of a contact layer with well-defined material properties enables firstly to increase the actual contact area in the bed-joints from 23% to 98% of the nominal contact area and secondly to increase the load-bearing capacity by 14 to 97%. In addition, the contact layer with an auxetic material shows a significant capacity in altering the lateral expansion in the block units. The outcomes show that although the bed joint roughness influences the stress distribution in a dry-stacked masonry block, a contact layer with well-defined material properties enables to overcome the roughness induced by the bed-joint imperfections. [less ▲]

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See detailExperimental and analytical analysis of the load-bearing capacity Pu of improved dry-stacked masonry
Chewe Ngapeya, Gelen Gael UL; Waldmann, Danièle UL

in Journal of Building Engineering (2020), 27

Dry-Stacked Masonry (DSM) as structural load-bearing element is still unexploited because of many factors including the early face-shell cracking, the impacts of the block imperfections on the wall load ... [more ▼]

Dry-Stacked Masonry (DSM) as structural load-bearing element is still unexploited because of many factors including the early face-shell cracking, the impacts of the block imperfections on the wall load-bearing capacity (Pu) and the lack of design code safely predicting Pu. Through experimental tests, this paper investigates a strategy for improving Pu of DSM by placing an additional horizontal contact layer on the top face of raw DSM blocks. The effect of four mixtures used to improve the raw DSM blocks has been investigated. Further, a mathematical model predicting Pu is proposed which takes into account the effects of the block imperfections. In the course of the investigation, 20 DSM wallets and 25 DSM prisms built with raw and improved DSM blocks were tested to failure under axial compression. In the former, the face-shell cracking load (Pcrack) and the load-bearing capacity (Pu) were recorded, while in the latter, the actual contact area was recorded in hundred full bed-joints using Prescale Fujifilm strips. The results showed that a contact layer of well-defined properties increased the actual contact area from 23% to 55% and improved Pu by 31,9%. The mathematical model for the raw DSM blocks predicts Pu with a mean accuracy of 93% and a standard deviation of 12% where the standards EN 1996-1-1 for mortared masonry exhibited a mean accuracy of 137% and a standard deviation of about 29%. Concerning the improved DSM blocks, the proposed model predicts Pu with a mean accuracy of 106% and a standard deviation of 10%, whereas the standards EN 1996-1-1 presents a mean accuracy of 124% and a standard deviation of 9%. [less ▲]

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See detailGravel wash mud, a quarry waste material as supplementary cementitious material (SCM)
Thapa, Vishojit Bahadur UL; Waldmann, Danièle UL; Simon, Claude

in Cement and Concrete Research (2019), 124(105833),

The suitability of gravel wash mud (GWM), a sludge waste from gravel quarrying, is examined for its use as a partial Ordinary Portland cement (OPC) clinker substitute. The gravel wash mud was dried ... [more ▼]

The suitability of gravel wash mud (GWM), a sludge waste from gravel quarrying, is examined for its use as a partial Ordinary Portland cement (OPC) clinker substitute. The gravel wash mud was dried, milled into a fine powder and calcined at 750°C, 850°C and 950°C. In this study, various characterisation methods including particle size distribution (PSD), X-ray fluorescence (XRF), X-ray diffraction (XRD) and the simultaneous thermal analysis (STA) were applied on the calcined GWM powders to determine the optimal calcination temperature. Over 200 specimens were prepared based on different cement paste and mortar mixes to investigate the potential of calcined GWM powders as SCMs. The pozzolanic activity of the GWM powders was verified by applying strength-based evaluation methods, simultaneous thermal analysis and SEM on hardened samples. Very promising strength-enhancing capacities were observed for samples containing GWM powders calcined at 850°C with a OPC replacement level of 20 wt.%. [less ▲]

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See detailA material and component bank to facilitate material recycling and component reuse for a sustainable construction: concept and preliminary study
Cai, Gaochuang; Waldmann, Danièle UL

in Clean Technologies and Environmental Policy (2019)

This paper concerns the reusable components and recycled materials from demounted structures 16 which may draw a large amount of waste in construction industry. By a series of literature review 17 and ... [more ▼]

This paper concerns the reusable components and recycled materials from demounted structures 16 which may draw a large amount of waste in construction industry. By a series of literature review 17 and analyses, a material and component bank was proposed to manage more effectively the 18 recycling of materials and direct reuse of components even of whole components obtained from 19 old structures to facilitate a more sustainable construction industry. The concept, main businesses 20 and work operation of the bank were illustrated in detail including its potential management 21 method and supply chain. The relationship between the bank and current building information 22 modelling, design for deconstruction, supply chain and life cycle assessment based on the bank 23 were then analysed in detail. It can be concluded that the bank could pave the way for effectively 24 performing a further and repaid reuse of components and perfecting current recycling of materials 25 to contribute a more sustainable built environment from the view of various terms mentioned in 26 this study. The bank also can link with current method of life cycle assessment or environmental 27 impact assessment well, which all can promote the construction sustainability indicating the bank 28 can be integrated into current construction industry easily for the future. [less ▲]

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See detailModelling of interfacial crack propagation in strongly heterogeneous materials by using phase field method
Nguyen, Thanh-Tung; Yvonnet, Julien; Waldmann, Danièle UL et al

in Proceedings of the 8th GACM Colloquium on Computational Mechanics for Young Scientists from Academia and Industry (2019, August 28)

Phase field model has been proved to be a useful tool to study the fracture behaviors in heterogeneous materials. This method is able to model complex, multiple crack fronts, and branching in both 2D/3D ... [more ▼]

Phase field model has been proved to be a useful tool to study the fracture behaviors in heterogeneous materials. This method is able to model complex, multiple crack fronts, and branching in both 2D/3D without ad-hoc numerical treatments. In this study, a new interfacial cracking model in the phase field framework is proposed. The effects of both stiff and soft interphases on the fracture response of composite materials are considered. A dimensional-reduced model based on a rigorous asymptotic analysis is adapted to derive the null thickness imperfect interface models from an original configuration containing thin interphase. The idea of mixing the bulk and interfacial energy within the phase field framework is then used to describe the material degradation both on the interface and in bulk. Moreover, in order to ensure the physical crack propagation patterns, a unilateral contact condition is also proposed for the case of spring imperfect interface. The complex cracking phenomena on interfaces such as initiation, delamination, coalescence, deflection, as well as the competition between the interface and bulk cracking are successfully predicted by the present method. Concerning the numerical aspect, the one-pass staggered algorithm is adapted, providing an extremely robust approach to study interfacial cracking phenomena in a broad class of heterogeneous materials. [less ▲]

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See detailPotential of the Deformation Area Difference (DAD)-Method for Condition Assessment of Bridge Structures
Waldmann, Danièle UL; Erdenebat, Dolgion UL

Scientific Conference (2019, August 27)

The construction industry ranks in the back rows in terms of digitalization. The numerous existing bridge structures require considerable effort for inspection and reliable assessment of their condition ... [more ▼]

The construction industry ranks in the back rows in terms of digitalization. The numerous existing bridge structures require considerable effort for inspection and reliable assessment of their condition. However, the state-of-the-art for inspecting these structures still relies on the visual inspection realized by bridge inspectors. The current paper summarizes several research projects in the field of condition assessment of bridge structures at the University of Luxembourg by analysing the structural response due to dynamic excitation and static loading tests. The latest development aims at using the most modern measurement techniques by combining them to a new method, the Deformation Area Difference (DAD)-Method in order to simplify and automatize at most the inspection process. The proposed DAD-Method is based on conventional static load deflection tests. It allows the localization of stiffness-reducing damage by using a very precise measurement of the deflection line and by combining this outcome to the deflection line generated by a simplified finite element model of the bridge. In order to investigate the condition of a bridge by the DAD-Method modern measurement techniques such as photogrammetry and laser scanning are used. In the framework of the conducted research, these techniques are also compared to traditional measurement systems such as total station and inductive displacement sensors as well as to digital levelling sensors. By theoretical examples and experimental tests, it can be shown that the DAD-Method is able to detect and localize damage when the damage level is dominant on the measurement noise. This paper investigates also the application of the method on a real bridge structure in Luxembourg. All of the above-mentioned measurement techniques were used, whereby the photogrammetry is applied using both, stable tripods and an autonomous flying drone. This allows examining the accuracy of the different measurement systems when applied on a real-size structure. [less ▲]

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See detailKeynote lecture: Potential of the Deformation Area Difference (DAD)-Method for Condition Assessment of Bridge Structures
Waldmann, Danièle UL; Erdenebat, Dolgion

in Proceedings of SMAR 2019 - Fifth Conference on Smart Monitoring, Assessment and Rehabilitation of Civil Structures (2019, August)

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See detailComputational chemo-thermo-mechanical coupling phase-field model for complex fracture induced by early-age shrinkage and hydration heat in cement-based materials
Nguyen, Thanh Tung UL; Waldmann, Danièle UL; Bui, T. Q.

in Computer Methods in Applied Mechanics and Engineering (2019), 348

In this paper, we present a new multi-physics computational framework that enables us to capture and investigate complex fracture behavior in cement-based materials at early-age. The present model ... [more ▼]

In this paper, we present a new multi-physics computational framework that enables us to capture and investigate complex fracture behavior in cement-based materials at early-age. The present model consists of coupling the most important chemo-thermo-mechanical processes to describe temperature evolution, variation of hydration degree, and mechanical behavior. The changes of material properties are expressed as a function of the hydration degree, to capture the age effects. Fracture analysis of these processes are then accommodated by a versatile phase field model in the framework of smeared crack models, addressing the influence of cracks on hydration and thermal transfer. We additionally describe a stable and robust numerical algorithm, which aims to solve coupled problems by using a staggered scheme. The developed approach is applied to study the fracture phenomena at both macroscopic and mesoscopic scales, in which all microstructural heterogeneities of sand and cement matrix are explicitly accounted. Nucleation, initiation, and propagation of complex crack network are simulated in an efficient way demonstrating the potential of the proposed approach to assess the early-age defects in concrete structures and materials. [less ▲]

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See detailCurvature based DAD-method for damage localisation under consideration of measurement noise minimisation
Erdenebat, Dolgion UL; Waldmann, Danièle UL; Teferle, Felix Norman UL

in Engineering Structures (2019), 181

Several research projects on condition assessment of bridges have proven that structural responses from dynamic excitation or static loading are influenced by local damages and thus, could be used for the ... [more ▼]

Several research projects on condition assessment of bridges have proven that structural responses from dynamic excitation or static loading are influenced by local damages and thus, could be used for the detection and localisation of damages. Particularly, the curvature of structures is directly depending on their stiffness. In order to localise the discontinuities in curvature lines resulting from damage, this paper uses the so-called Deformation Area Difference Method (DAD), which is based on static load deflection tests on bridge structures. The DAD-method for damage localisation is presented within the paper using a theoretical example, which is then verified by two laboratory experiments. The first experiment consists of a reinforced concrete beam, which is loaded stepwise until failure of the concrete in the compression zone. Due to the load increase, the tensile zone of the beam starts cracking, leading to a stiffness reduction. The application of the DAD-method allows identifying the cracked area from the measurement of the deflection line. However, a challenge and a prerequisite for the applicability of the DAD-method is the highly accurate measurement of the deflection line. Therefore, one of the most modern measurement techniques such as digital photogrammetry is applied. Nonetheless, the accuracy of each measurement technique is limited. The second laboratory experiment consists of a steel beam, which is locally damaged at three positions. The degree of the damage is stepwise increased in order to identify at which degree of damage the applied DAD-method is still able to identify and localise damage. In this work, the focus lies on the minimisation of the effect of noise resulting from the limited measurement precision. Possible solutions were examined and proposed based on methods such as data smoothing using polynomial regression, consideration of standard deviation and measurement point variation. The reduction of the noise effect leads to an increase in the sensitivity of the damage localisation. The DAD-method has proven its potential for practical application through the successful localisation of cracking in the concrete beam. [less ▲]

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See detailExperimental and numerical analysis of early age behavior in non-reinforced concrete
Nguyen, Thanh Tung UL; Weiler, Michael UL; Waldmann, Danièle UL

in Construction and Building Materials (2019), 210

An approach combining numerical simulations and experimental techniques is proposed to investigate the early-age properties of non-reinforced concrete. Both thermo-mechanical and fracture behaviors are ... [more ▼]

An approach combining numerical simulations and experimental techniques is proposed to investigate the early-age properties of non-reinforced concrete. Both thermo-mechanical and fracture behaviors are studied, providing a deep insight into the hydration process. This work makes an important step in understanding the effects of hydration on the performance of cement-based materials. More specifically, in the first part, the shrinkage and fracture properties of a non-reinforced concrete have been experimentally considered, along with the characterization of several material parameters. The experimental results exhibit a high risk of early-age cracking for this kind of concrete. Especially, the fracture phenomena are complex, including multi-evolution-stages, initiation, propagation, stop-growing, and re-growing. In the second part, the computational modeling based on the phase field method of failure mechanism is applied to simulate the thermal, mechanical and fracture behavior due to early-age hydration. A detailed discussion on the identification of model/material parameters and the construction of numerical model including the boundary conditions is given. We provide the following comparison between predictions of the numerical simulation with the experimental observations. An excellent predictive capability of the computational model is noted. More importantly, this work demonstrates the performance of the proposed approach, which requires only a few tests to identify the model inputs. Most of the chemo-thermal parameters can be theoretically determined based on the concrete mix and the chemical/mineral compositions of the cement. [less ▲]

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See detailBehaviour of Circular Fiber-Reinforced Polymer-Steel-Confined Concrete Columns Subjected to Reversed Cyclic Loads: Experimental Studies and FE Analysis
Wang, Yanlei; Cai, Gaochuang; Waldmann, Danièle UL et al

in Journal of Structural Engineering (2019)

This paper studies experimentally the behaviour of circular FRP-steel-confined columns subjected to reversed cyclic loads. The influence of main structural factors on the cyclic behaviour of the columns ... [more ▼]

This paper studies experimentally the behaviour of circular FRP-steel-confined columns subjected to reversed cyclic loads. The influence of main structural factors on the cyclic behaviour of the columns is discussed. Test results show the outstanding seismic performance of FRP-steel confined reinforced concrete (RC) and steel-reinforced concrete (SRC) column. The lateral confinement effectiveness of FRP materials is verified in the steel tube confined RC columns. A simplified finite element method (FEM) model supported by OpenSees is developed to simulate the experimental results of the test columns. Based on the proposed FEM model, a parametric analysis is conducted for investigating the effects of several main factors on the reversed cyclic behaviour of GFRP-steel confined RC columns. Based on the test and numerical analyses, the study discusses the influence of variables such as the lateral confinement on the plastic hinge region and peak drift ratio of the studied concrete columns under reversed cyclic loads. Results indicate that the lateral confinement significantly affects the height of plastic hinge region of circular confined columns without H-steel. Based on the analysies of test data from the study and literature, the paper suggests a simple model to predict the peak drift ratio of the confined RC columns. [less ▲]

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See detailPhase field modeling of interfacial damage in heterogeneous media with stiff and soft interphases
Nguyen, Thanh Tung UL; Yvonnet, Julien; Waldmann, Danièle UL et al

in Engineering Fracture Mechanics (2019), 218

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See detailPhase field modeling of interfacial crack propagation in quasi-brittle heterogeneous materials
Nguyen, Thanh Tung UL; Yvonnet, Julien; Waldmann, Danièle UL et al

in International Conference on Computational Modeling of Fracture and Failure of Materials and Structures (2019)

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See detailPhase field modeling of crack initiation and propagation under complex loading
Nguyen, Thanh Tung UL; Yvonnet, Julien; Waldmann, Danièle UL

in International Conference on Computational Modeling of Fracture and Failure of Materials and Structures (2019)

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See detailRole of interfacial transition zone in phase field modeling of fracture in layered heterogeneous structures
Nguyen, Thanh Tung UL; Waldmann, Danièle UL; Bui, T. Q.

in Journal of Computational Physics (2019), 386

Mechanical behavior of layered materials and structures greatly depends on the mechanical behavior of interfaces. In the past decades, the failure in such layered media has been studied by many ... [more ▼]

Mechanical behavior of layered materials and structures greatly depends on the mechanical behavior of interfaces. In the past decades, the failure in such layered media has been studied by many researchers due to their critical role in the mechanics and physics of solids. This study aims at investigating crack-interface interaction in two-dimensional (2-D) and three-dimensional (3-D) layered media by a phase field model. Our objectives are fourfold: (a) to better understand fracture behavior in layered heterogeneous systems under quasi-static load; (b) to introduce a new methodology for better describing interfaces by a regularized interfacial transition zone in the context of varia-tional phase field approach, exploring its important role; (c) to show the accuracy , performance and applicability of the present model in modeling material failure at the interfaces in both 2-D and 3-D bodies; and (d) to quantitatively validate computed crack path with respect to experimental data. Phase field models with both perfectly and cohesive bonded interfaces are thus derived. A regularized interfacial transition zone is introduced to capture characteristics of material mismatch at the interfaces. Numerical examples for 2-D and 3-D layered systems with experimental validation provide fundamentals of fracture behavior in layered structures. The obtained results shed light on the behavior of crack paths, which are drastically affected by the elastic modulus mismatch between two layers and interface types, and reveal the important role of the proposed interfacial transition zone in phase field modeling of crack interface interactions. [less ▲]

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See detailStatic load deflection experiment on a beam for damage detection using the Deformation Area Difference Method
Erdenebat, Dolgion UL; Waldmann, Danièle UL; Teferle, Felix Norman UL

Scientific Conference (2018, October)

A reliable and safety infrastructure for both transport and traffic is becoming increasingly important today. The condition assessment of bridges remains difficult and new methods must be found to provide ... [more ▼]

A reliable and safety infrastructure for both transport and traffic is becoming increasingly important today. The condition assessment of bridges remains difficult and new methods must be found to provide reliable information. A meaningful in-situ assessment of bridges requires very detailed investigations which cannot be guaranteed by commonly used methods. It is known that the structural response to external loading is influenced by local damages. However, the detection of local damage depends on many factors such as environmental effects (e.g. temperature), construction layer (e.g. asphalt) and accuracy of the structural response measurement. Within the paper, a new so-called Deformation Area Difference (DAD) Method is presented. The DAD method is based on a load deflection experiment and does not require a reference measurement of initial condition. Therefore, the DAD method can be applied on existing bridges. Moreover, the DAD method uses the most modern technologies such as high precision measurement techniques and attempts to combine digital photogrammetry with drone applications. The DAD method uses information given in the curvature course from a theoretical model of the structure and compares it to real measurements. The paper shows results from a laboratory load-deflection experiment with a steel beam which has been gradually damaged at distinct positions. The load size is chosen so that the maximum deflection does not exceed the serviceability limit state. With the data obtained by the laboratory experiment, the damage degree, which can still be detected by the DAD method, is described. Furthermore, the influence of measurement accuracy on damage detection is discussed. [less ▲]

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See detailAssessment of the suitability of gravel wash mud as raw material for the synthesis of an alkali-activated binder
Thapa, Vishojit Bahadur UL; Waldmann, Danièle UL; Wagner, Jean-Frank et al

in Applied Clay Science (TOP10 Journal in Mineralogy) (2018), 161(C), 110-118

Gravel wash mud (GWM), a waste product from gravel mining was dried and processed into a fine powder to be activated by different concentrations of sodium hydroxide (NaOH) solutions for the synthesis of ... [more ▼]

Gravel wash mud (GWM), a waste product from gravel mining was dried and processed into a fine powder to be activated by different concentrations of sodium hydroxide (NaOH) solutions for the synthesis of an alkali-activated binder. The GWM powders were thermally treated at five different calcination temperatures 550, 650, 750, 850 and 950°C. The characterisation of the raw material comprises the particle size distribution (PSD) by laser granulometry, the chemical and mineralogical composition by X-ray fluorescence and X-ray diffraction analysis respectively, and simultaneous thermal analysis. The performance of the alkali-activated binders was examined using compression strength tests and the microstructure was observed using scanning electron microscopy (SEM). The GWM was classified as an aluminosilicate raw material with kaolinite and illite as main clay minerals. Furthermore, a mean particle size around 6.50μm was determined for the uncalcined and calcined GWM powders. The SEM images of the developed binders showed the formation of a compact microstructure, however, relatively low strengths were achieved. This preliminary study highlights an example of an aluminosilicate prime material, which shows very promising chemical and mineralogical characteristics, but its suitability for alkaline activation without further additives was not confirmed as far as performance-based criteria are considered. [less ▲]

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See detailBloc pour construction seche
Waldmann, Danièle UL; Chewe Ngapeya, Gelen Gael UL; Spina, Carlo et al

Patent (2018)

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See detailImpact of the height imperfections of masonry blocks on the load bearing capacity of dry-stack masonry walls
Chewe Ngapeya, Gelen Gael UL; Waldmann, Danièle UL; Scholzen, Frank UL

in Journal of Construction and Building Materials (TOP10 journal) (2018), 165

Dry-stacked masonry walls gives rise to geometric imperfections: the height variation of different masonry blocks ΔH and the roughness of the support area Δh. This paper studies the effect of ΔH on the ... [more ▼]

Dry-stacked masonry walls gives rise to geometric imperfections: the height variation of different masonry blocks ΔH and the roughness of the support area Δh. This paper studies the effect of ΔH on the structural response and the load bearing capacity of masonry walls by highlighting the load percolation. Furthermore, an algorithm was developed to define a stress multiplier coefficient respecting the imperfections ΔH. The algorithm allowed predicting 77% of the amplified stress compared to the FE analysis and showed that the geometric imperfections govern the load percolation in a wall as well as the cracking mode and the bearing capacity. [less ▲]

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See detailA short review on alkali-activated binders and geopolymer binders
Waldmann, Danièle UL; Thapa, Vishojit Bahadur UL

in Pahn, Matthias; Thiele, Catherina; Glock, Christian (Eds.) Vielfalt im Massivbau - Festschrift zum 65. Geburtstag von Prof. Dr. Ing. Jürgen Schnell (2018)

In the recent years, the trend for reusing waste products or industrial by-products to reduce the amount of Ordinary Portland Cement (OPC) in concrete constructions has become an important task for ... [more ▼]

In the recent years, the trend for reusing waste products or industrial by-products to reduce the amount of Ordinary Portland Cement (OPC) in concrete constructions has become an important task for industries and research institutions. OPC is the second most used material in the world after water and statistics confirm that the life cycle of OPC contributes to the generation of up to 5% of the annual CO2 emissions worldwide. Mostly responsible for this negative environmental performance of OPC are the high CO2 emissions related to the cement production processes, namely the deacidification of limestone and the burning of the clinker raw materials at high temperatures above 1400°C. The current demand for cementitious binder is higher than ever whereas the incentive of building sustainable and robust constructions is gaining increasingly in importance. There is a need for development of new more durable and environmental friendly binders as an alternative to OPC binders. Therefore, the research on cement alternatives has risen over the last decades and a lot of research work has been carried out to fulfil the requirements of the market. In this work, the concepts of alkali activated materials and geopolymers are presented, and their properties are compared and discussed. A short historical review is given. Furthermore, the reaction mechanisms and hydration products of these binders are characterized and explained by referring to literature. Finally, novel binders based on waste materials are presented before closing with a short outlook on remaining questions and future challenges. [less ▲]

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