Materials

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19 pages, 7689 KiB

Open AccessArticle

Investigation on Hydration and Mechanical Properties of Mortar Containing Limestone Powder and Fly Ash Based on the Coupled Chemical–Thermal–Mechanical Method

by Wei Zhou, Wenxiang Tian, Tianqi Qi, Shuhua Liu, Chuqiao Feng, Gang Ma and Xiaolin Chang

Materials 2020, 13(19), 4387; https://doi.org/10.3390/ma13194387 - 01 Oct 2020

Cited by 4 | Viewed by 2060

Abstract

The composited cementitious materials usually have superior performance; for example, using limestone powder (LP) and fly ash (FA) as the admixtures of cement in concrete/mortar is a popular way of improving the properties of concrete/mortar structures. In this work, we performed experimental tests [...] Read more.

The composited cementitious materials usually have superior performance; for example, using limestone powder (LP) and fly ash (FA) as the admixtures of cement in concrete/mortar is a popular way of improving the properties of concrete/mortar structures. In this work, we performed experimental tests to study the hydration process and pore distribution in mortar containing different ratios of LP and FA. Based on the results of mercury intrusion porosimetry (MIP), a numerical mortar model with random pore is built. The model can reflect the synergistic hydration interaction and filling effect caused by the admixtures of LP and FA. After analyzing the hydration process, the coupled chemical–thermal–mechanical method was used to simulate the characteristics of mortar containing LP and FA. The coupling model can simulate the “hump-type” hydration acceleration stage of the mortar at early age, which is specifically caused by the LP, proved in the experimental test. Additionally, the special, “hump-type” stage is important to enhance the early strength of the mortar. At different levels of admixture content, the random pore model and coupled method can predict the evolution process of the mechanical properties well, at early age and for long-term strength. Both experimental and numerical results suggest that the mortar containing admixtures of the proper ratio of LP to FA have good mechanical properties, which can be applied to engineering structures. Full article

(This article belongs to the Special Issue Modeling of Cementitious Materials and Structures)

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12 pages, 2381 KiB

Open AccessArticle

THz Fingerprints of Cement-Based Materials

by Jorge S. Dolado, Guido Goracci, Eduardo Duque, Pavel Martauz, Yibing Zuo and Guang Ye

Materials 2020, 13(18), 4194; https://doi.org/10.3390/ma13184194 - 21 Sep 2020

Cited by 9 | Viewed by 2477

Abstract

To find materials with an appropriate response to THz radiation is key for the incoming THz technology revolution. Unfortunately, this region of the electromagnetic spectra remains largely unexplored in most materials. The present work aims at unveiling the most significant THz fingerprints of [...] Read more.

To find materials with an appropriate response to THz radiation is key for the incoming THz technology revolution. Unfortunately, this region of the electromagnetic spectra remains largely unexplored in most materials. The present work aims at unveiling the most significant THz fingerprints of cement-based materials. To this end transmission experiments have been carried out over Ordinary Portland Cement (OPC) and geopolymer (GEO) binder cement pastes in combination with atomistic simulations. These simulations have calculated for the first time, the dielectric response of C-S-H and N-A-S-H gels, the most important hydration products of OPC and GEO cement pastes respectively. Interestingly both the experiments and simulations reveal that both varieties of cement pastes exhibit three main characteristic peaks at frequencies around ~0.6 THz, ~1.05 THz and ~1.35 THz, whose origin is governed by the complex dynamic of their water content, and two extra signals at ~1.95 THz and ~2.75 THz which are likely related to modes involving floppy parts of the dried skeleton. Full article

(This article belongs to the Special Issue Modeling of Cementitious Materials and Structures)

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18 pages, 19600 KiB

Open AccessArticle

Effect of Zeolite on Shrinkage and Crack Resistance of High-Performance Cement-Based Concrete

by Nguyen Cong Thang, Nguyen Van Tuan, Keun-Hyeok Yang and Quoc Tri Phung

Materials 2020, 13(17), 3773; https://doi.org/10.3390/ma13173773 - 26 Aug 2020

Cited by 15 | Viewed by 2231

Abstract

This study examined the effectiveness of zeolite addition to reduce the autogenous shrinkage of high-performance cement-based concrete (HPC). The zeolites were replaced up to 15% of the cement content by weight and their mean particle size varied from 5.6 to 16.7 µm. To [...] Read more.

This study examined the effectiveness of zeolite addition to reduce the autogenous shrinkage of high-performance cement-based concrete (HPC). The zeolites were replaced up to 15% of the cement content by weight and their mean particle size varied from 5.6 to 16.7 µm. To evaluate the crack resistance of HPC containing zeolites, the ring tests and internal relative humidity measurements were performed at different ages. The compressive strengths were determined at 3, 7, 28 and 90 days of curing. Test results confirmed that the addition of zeolite was promising and favourable in enhancing the compressive strength, crack resistance and reducing the autogenous shrinkage of HPC due to synergistic pozzolanic and internal curing effects. The autogenous shrinkage tended to decrease with the increase in zeolite content and its particle size. In addition, the extent of the autogenous shrinkage development at the early ages decreased with higher zeolite content replaced. Furthermore, to predict the autogenous shrinkage of HPC containing zeolite, an improved model has been proposed, in which the conventional ultimate autogenous shrinkage strain and time function were modified by introducing new parameters accounting for the zeolite content and its particle size. It appeared that the proposed model was able to capture the autogenous shrinkage behaviour of HPC with or without zeolite, while the fib 2010 model underestimated the autogenous shrinkage of HPC containing less than 10% zeolite replacement. Full article

(This article belongs to the Special Issue Modeling of Cementitious Materials and Structures)

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11 pages, 1952 KiB

Open AccessArticle

Development of Crystallinity of Triclinic Polymorph of Tricalcium Silicate

by Simona Ravaszová and Karel Dvořák

Materials 2020, 13(17), 3734; https://doi.org/10.3390/ma13173734 - 24 Aug 2020

Cited by 4 | Viewed by 2145

Abstract

Tricalcium silicate phase is one of the main components of modern Portland cements. One of the major industrial challenges in the field of cement production is mapping the influence of individual clinker minerals and their polymorphs on the properties of industrially produced clinkers. [...] Read more.

Tricalcium silicate phase is one of the main components of modern Portland cements. One of the major industrial challenges in the field of cement production is mapping the influence of individual clinker minerals and their polymorphs on the properties of industrially produced clinkers. The primary goal of this work is to improve the fundamental knowledge of understanding the process of alite formation and development from a crystallographic point of view. This study focuses on the observation of the crystallization process of triclinic alite during the firing process, which to date has not been thoroughly described. The effects of a wide range of temperatures and sintering periods on crystallinity were assessed on samples fired in platinum crucibles in a laboratory furnace. X-ray analysis—together with calculation of crystallinity using Scherrer’s equation—was used for observing the crystallite size changes of T1 alite polymorph. According to the acquired results, among the most technologically and economically advantageous regimes of production of a high-quality triclinic alite is the temperature of 1450 °C and sintering time of two hours. The most significant changes in the crystallite size occurred within the first hour of sintering for the whole investigated temperature range. Full article

(This article belongs to the Special Issue Modeling of Cementitious Materials and Structures)

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23 pages, 20127 KiB

Open AccessArticle

Experimental Research on Viscosity Characteristics of Grouting Slurry in a High Ground Temperature Environment

by Jiandong Niu, Bin Wang, Chu Feng and Kang Chen

Materials 2020, 13(14), 3221; https://doi.org/10.3390/ma13143221 - 20 Jul 2020

Cited by 17 | Viewed by 2865

Abstract

The grouting method is a technical means to prevent and control the thermal damage of the tunnel with high ground temperature in the underground hot water area, and the viscosity characteristic of the slurry is the key factor of grouting treatment. When grouting [...] Read more.

The grouting method is a technical means to prevent and control the thermal damage of the tunnel with high ground temperature in the underground hot water area, and the viscosity characteristic of the slurry is the key factor of grouting treatment. When grouting in high ground temperature geological conditions, the slurry inevitably has both time-varying and temperature-varying characteristics of viscosity in the process of filling high-temperature fissures and plugging geothermal water. At present, the research on the viscosity characteristics of slurry at high temperature is rarely reported in the literature. In this paper, laboratory tests were carried out to measure the time-varying viscosity of ordinary cement slurry; cement-sodium silicate slurry, widely used in engineering; and high ground temperature grouting slurry (HGTGS), independently developed by our research group, at different preheating temperatures (20, 40, 60, 80 °C). The viscosity function curves of the three kinds of slurry were obtained by function fitting method, and the viscosity variation law of slurry was analyzed. The study found that the time-varying process of viscosity of the cement-sodium silicate slurry and the HGTGS in specific temperature conditions can be divided into two stages: The slow rising period of viscosity and the rapid rising period of viscosity. Whereas, the time-varying process of viscosity of ordinary cement slurry in specific temperature conditions includes only one stage of the slow rising period of viscosity. The viscosity of ordinary cement slurry and cement-sodium silicate slurry increases with the increase of temperature, while the viscosity of the HGTGS decreases with the increase of temperature. There are corresponding viscosity time-varying equations for the three kinds of slurry in different temperature conditions. The viscosity time-varying equation of the ordinary cement slurry accords with the linear function form, and the viscosity time-varying equation of the cement-sodium silicate slurry accords with the power-law function form. The viscosity time-varying equation of the HGTGS conforms to the exponential function form. On this basis, the unified description equation of the viscosity characteristics of grouting slurry in high ground temperature and the applicability of different types of grouting materials are obtained. This study has a certain reference value and guidance for theoretical analysis, numerical simulation and engineering application of grouting in high ground temperature environment. Full article

(This article belongs to the Special Issue Modeling of Cementitious Materials and Structures)

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22 pages, 3710 KiB

Open AccessArticle

Influence of Micro-Pore Connectivity and Micro-Fractures on Calcium Leaching of Cement Pastes—A Coupled Simulation Approach

by Janez Perko, Neven Ukrainczyk, Branko Šavija, Quoc Tri Phung and Eddie A. B. Koenders

Materials 2020, 13(12), 2697; https://doi.org/10.3390/ma13122697 - 13 Jun 2020

Cited by 11 | Viewed by 2234

Abstract

A coupled numerical approach is used to evaluate the influence of pore connectivity and microcracks on leaching kinetics in fully saturated cement paste. The unique advantage of the numerical model is the ability to construct and evaluate a material with controlled properties, which [...] Read more.

A coupled numerical approach is used to evaluate the influence of pore connectivity and microcracks on leaching kinetics in fully saturated cement paste. The unique advantage of the numerical model is the ability to construct and evaluate a material with controlled properties, which is very difficult under experimental conditions. Our analysis is based on two virtual microstructures, which are different in terms of pore connectivity but the same in terms of porosity and the amount of solid phases. Numerical fracturing was performed on these microstructures. The non-fractured and fractured microstructures were both subjected to chemical leaching. Results show that despite very different material physical properties, for example, pore connectivity and effective diffusivity, the leaching kinetics remain the same as long as the amount of soluble phases, i.e., buffering capacity, is the same. The leaching kinetics also remains the same in the presence of microcracks. Full article

(This article belongs to the Special Issue Modeling of Cementitious Materials and Structures)

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20 pages, 2674 KiB

Open AccessArticle

Feature Importance of Stabilised Rammed Earth Components Affecting the Compressive Strength Calculated with Explainable Artificial Intelligence Tools

by Hubert Anysz, Łukasz Brzozowski, Wojciech Kretowicz and Piotr Narloch

Materials 2020, 13(10), 2317; https://doi.org/10.3390/ma13102317 - 18 May 2020

Cited by 31 | Viewed by 3525

Abstract

Cement-stabilized rammed earth (CSRE) is a sustainable construction material. The use of it allows for economizing on the cost of a structure. These two properties of CSRE are based on the fact that the soil used for the rammed mixture is usually dug [...] Read more.

Cement-stabilized rammed earth (CSRE) is a sustainable construction material. The use of it allows for economizing on the cost of a structure. These two properties of CSRE are based on the fact that the soil used for the rammed mixture is usually dug close to the construction site, so it has random characteristics. That is the reason for the lack of widely accepted prescriptions for CSRE mixture, which could ascertain high enough compressive strength. Therefore, assessing which components of CSRE have the highest impact on its compressive strength becomes an important issue. There are three machine learning regression tools, i.e., artificial neural networks, decision tree, and random forest, used for predicting the compressive strength based on the relative content of CSRE composites (clay, silt, sand, gravel, cement, and water content). The database consisted of 434 samples of CSRE, which were prepared and crushed for testing purposes. Relatively low prediction errors of aforementioned models allowed for the use of explainable artificial intelligence tools (drop-out loss, mean squared error reduction, accumulated local effect) to rank the influence of the ingredients on the dependent variable—the compressive strength. Consistent results from all above-mentioned methods are discussed and compared to some statistical analysis of selected features. This innovative approach, helpful in designing the construction material is a solid base for reliable conclusions. Full article

(This article belongs to the Special Issue Modeling of Cementitious Materials and Structures)

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16 pages, 4059 KiB

Open AccessArticle

Early-Age Properties of Concrete Based on Numerical Hydration Modelling: A Parametric Analysis

by Marco Pepe, Carmine Lima and Enzo Martinelli

Materials 2020, 13(9), 2112; https://doi.org/10.3390/ma13092112 - 02 May 2020

Cited by 7 | Viewed by 1970

Abstract

The early-age performances of cement-based mixtures are governed by cement hydration reactions. As a matter of fact, the heat generated during the setting and hardening phases due to the hydration processes increases the temperatures within the concrete elements while it starts developing its [...] Read more.

The early-age performances of cement-based mixtures are governed by cement hydration reactions. As a matter of fact, the heat generated during the setting and hardening phases due to the hydration processes increases the temperatures within the concrete elements while it starts developing its mechanical properties. These thermal stresses can cause the premature cracking of the cementitious matrix and undermine the long-term durability of the whole concrete element, especially in the case of massive structures where the dissipation of generated heat is more difficult. It is worth highlighting that the kinetics of cement hydration is mainly governed by the mixture composition; on the other hand, the heat generated during the setting and hardening is also influenced by the geometry of the element and/or its curing conditions. In this context, this study presents a numerical procedure intended to simulate the hydration reactions, and hence scrutinize the development of concrete properties at the early-age. Specifically, considering the variation of several factors, such as concrete strength class, element size and curing conditions, a comprehensive parametric analysis is presented herein, leading to the proposal of a simplified approach for both predicting the time evolution of the concrete mechanical performances at the early-age and mitigating the risk of premature cracking. Full article

(This article belongs to the Special Issue Modeling of Cementitious Materials and Structures)

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21 pages, 9586 KiB

Open AccessArticle

Implementation of Numerical Mesostructure Concrete Material Models: A Dot Matrix Method

by Hao Xie and Jili Feng

Materials 2019, 12(23), 3835; https://doi.org/10.3390/ma12233835 - 21 Nov 2019

Cited by 7 | Viewed by 2445

Abstract

We develop a dot matrix method (DMM) using the principles of computational geometry to place aggregates into matrices for the construction of mesolevel concrete models efficiently and rapidly. The basic idea of the approach is to transform overlap detection between polygons (or polyhedrons) [...] Read more.

We develop a dot matrix method (DMM) using the principles of computational geometry to place aggregates into matrices for the construction of mesolevel concrete models efficiently and rapidly. The basic idea of the approach is to transform overlap detection between polygons (or polyhedrons) into checking the possibility of any intersection between the point sets within a trial placement aggregate and the already placed ones in mortar. Through the arithmetic operation of integer point sets, the efficiency of the underlying algorithm in the dot matrix method is higher. Our parking algorithm holds several advantages comparing with the conventional placement issues. First, it is suitable for arbitrary-shape aggregate particles. Second, it only needs two sets for examining if the overlap between a trial placement aggregate and the already placed ones. Third, it accurately places aggregates according to aggregate grading curves, by order of reduction, led to more efficiently reducing aggregate placement time. The present method is independent of the size of aggregate particles. Combing with 3D laser scanning technology, the present method can also be used to create mesostructure concrete models conveniently and flexibly. Several examples show that DDM is a robust and valid method to construct mesostructure concrete models. Full article

(This article belongs to the Special Issue Modeling of Cementitious Materials and Structures)

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12 pages, 6028 KiB

Open AccessArticle

Relating Ettringite Formation and Rheological Changes during the Initial Cement Hydration: A Comparative Study Applying XRD Analysis, Rheological Measurements and Modeling

by Cordula Jakob, Daniel Jansen, Neven Ukrainczyk, Eddie Koenders, Ursula Pott, Dietmar Stephan and Jürgen Neubauer

Materials 2019, 12(18), 2957; https://doi.org/10.3390/ma12182957 - 12 Sep 2019

Cited by 58 | Viewed by 3769

Abstract

In order to gain a deeper understanding of the rheological development of hydrating ordinary Portland cement (OPC) pastes at initial state, and to better understand their underlying processes, quantitative X-ray diffraction (XRD) analysis and rheological measurements were conducted and their results combined. The [...] Read more.

In order to gain a deeper understanding of the rheological development of hydrating ordinary Portland cement (OPC) pastes at initial state, and to better understand their underlying processes, quantitative X-ray diffraction (XRD) analysis and rheological measurements were conducted and their results combined. The time-dependent relation between phase development and flow behavior of cement paste was investigated at two different temperatures (20 and 30 °C), over a period of two hours. Regarding the phase development during hydration, ettringite precipitation was identified as the dominant reaction in the first two hours. For both temperatures, the increasing ettringite content turned out to correlate very well with the loss of workability of the reacting cement paste. An exponential relationship between ettringite growth and flow behavior was observed that could be explained by applying the Krieger-Dougherty equation, which describes the influence of solid fraction on the viscosity of a suspension. Full article

(This article belongs to the Special Issue Modeling of Cementitious Materials and Structures)

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28 pages, 22699 KiB

Open AccessArticle

Validation and Investigation on the Mechanical Behavior of Concrete Using a Novel 3D Mesoscale Method

by Yuhang Zhang, Zhiyong Wang, Jie Zhang, Fenghua Zhou, Zhihua Wang and Zhiqiang Li

Materials 2019, 12(16), 2647; https://doi.org/10.3390/ma12162647 - 20 Aug 2019

Cited by 24 | Viewed by 3679

Abstract

The mechanical performance of concrete is strongly influenced by the geometry and properties of its components (namely aggregate, mortar, and Interfacial Transitional Zone (ITZ)) from the mesoscale viewpoint, and analyzing the material at that level should be a powerful tool for understanding macroscopic [...] Read more.

The mechanical performance of concrete is strongly influenced by the geometry and properties of its components (namely aggregate, mortar, and Interfacial Transitional Zone (ITZ)) from the mesoscale viewpoint, and analyzing the material at that level should be a powerful tool for understanding macroscopic behavior. In this paper, a simple and highly efficient method is proposed for constructing realistic mesostructures of concrete. A shrinking process based on 3D Voronoi tessellation was employed to generate aggregates with random polyhedron and grading size, and reversely, an extending procedure was applied for ITZ generation. 3D mesoscale numerical simulation was conducted under a quasi-static load using an implicit solver which demonstrated the good robustness and feasibility of the presented model. The simulated results resembled favorably the corresponding experiments both in stress–strain curves and failure modes. Damage evolution analysis showed that the ITZ phase has profound influence on the damage behavior of concrete as damage initially develops from here and propagates to mortar. In addition, it was found that tensile damage is the principal factor of mortar failure while compressive damage is the principal factor of ITZ failure under compression. Full article

(This article belongs to the Special Issue Modeling of Cementitious Materials and Structures)

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Graphical abstract

15 pages, 2662 KiB

Open AccessArticle

Nonlinear Stress-Strain Model for Confined Well Cement

by Yan Li, Yunhu Lu, Ramadan Ahmed, Baoguo Han and Yan Jin

Materials 2019, 12(16), 2626; https://doi.org/10.3390/ma12162626 - 17 Aug 2019

Cited by 10 | Viewed by 4335

Abstract

The cement sheath is the key for providing the zonal isolation and integrity of the wellbore. Oil well cement works under confining pressure, so it exhibits strong nonlinear and ductile behavior which is very different from that without confining pressure. Therefore, for the [...] Read more.

The cement sheath is the key for providing the zonal isolation and integrity of the wellbore. Oil well cement works under confining pressure, so it exhibits strong nonlinear and ductile behavior which is very different from that without confining pressure. Therefore, for the accuracy of the simulation and the reliability of well construction design, a reliable compression stress–strain model is essential for confined well cement. In this paper, a new axial stress–strain model for confined well cement is developed based on uniaxial and triaxial test data, examinations of failure mechanisms, and the results of numerical analysis. A parametric study was conducted to evaluate and calibrate the model. The model is simple and suitable for direct use in simulation studies and well design. Results from this study show the nonlinear compressive behavior of confined well cement can be predicted using the traditional uniaxial compressive strength test measurements. Full article

(This article belongs to the Special Issue Modeling of Cementitious Materials and Structures)

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24 pages, 9057 KiB

Open AccessArticle

Generalized Softened Variable Angle Truss Model for RC Hollow Beams under Torsion

by Luís Bernardo

Materials 2019, 12(13), 2209; https://doi.org/10.3390/ma12132209 - 09 Jul 2019

Cited by 3 | Viewed by 2502

Abstract

In recent studies, a new softened truss model called Generalized Softened Variable Angle Truss Model (GSVATM) has been proposed to compute the full torsional response of reinforced concrete (RC) rectangular solid beams under pure torsion. In this article, the GSVATM is extended to [...] Read more.

In recent studies, a new softened truss model called Generalized Softened Variable Angle Truss Model (GSVATM) has been proposed to compute the full torsional response of reinforced concrete (RC) rectangular solid beams under pure torsion. In this article, the GSVATM is extended to cover RC hollow beams under torsion. The modification of the calculation procedure, in order to account for the specific behavior of RC hollow beams for low loading levels, as well as the final solution procedure, is presented. The theoretical predictions from the extended GSVATM are compared with experimental results of RC hollow beams under torsion found in the literature. Good agreement is observed between the experimental and theoretical results, for both high and low loading levels. Full article

(This article belongs to the Special Issue Modeling of Cementitious Materials and Structures)

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Graphical abstract

8 pages, 3793 KiB

Open AccessArticle

Reactivity of Different Crystalline Surfaces of C₃S During Early Hydration by the Atomistic Approach

by K. M. Salah Uddin and Bernhard Middendorf

Materials 2019, 12(9), 1514; https://doi.org/10.3390/ma12091514 - 09 May 2019

Cited by 12 | Viewed by 2865

Abstract

Early hydration of tricalcium silicate (C₃S) has received great attention over the years due to the increased use of composite cement with a reduced number of clinker phases, especially the addition of what should be very reactive C₃S to [...] Read more.

Early hydration of tricalcium silicate (C₃S) has received great attention over the years due to the increased use of composite cement with a reduced number of clinker phases, especially the addition of what should be very reactive C₃S to guarantee early strength. Although many mechanisms have been proposed, the dissolution of polygonal C₃S at the material interface is not yet fully understood. Over the last decade, computational methods have been developed to describe the reaction in the cementitious system. This paper proposes an atomistic insight into the early hydration and the dissolution mechanism of calcium from different crystalline planes of C₃S using reactive force field (ReaxFF) combined with metadynamics (metaD). The reactivity and thermodynamic stability of different crystal planes were calculated from the dissolution profile of calcium during hydration at 298 K. The simulation results, clearly describe the higher reactivity of (

0 \bar{1} \bar{1}

), (011), (100), and

(\bar{1} 00)

surfaces of C₃S due to the strong interaction with the water, whereas, the dissolution profile explains the lower reactivity of (

\bar{1} \bar{1} 0

), (110), (

0 \bar{1} 0

) and the effect of water tessellation on the (001), (010) planes. Full article

(This article belongs to the Special Issue Modeling of Cementitious Materials and Structures)

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