Durability Of Cementitious Materials Research Articles

Freezing of water confined between calcium-silicate-hydrate layers: a coarse-grained molecular dynamics study

Freezing of water has a direct impact on the durability of cementitious materials, which include porous binding phases, like calcium-silicate-hydrate (CSH). Molecular dynamics (MD) simulations can capture behaviors of the water freezing in the pores and may give rise to insightful observations. In this work, the monoatomic water (mW) model and all-atom CSH model are combined to study low-temperature behavior of water molecules restricted within CSH layers. The developed model features good accuracy and accelerated computational rate, and is employed to study how ultra-confined water in CSH phases (≤6 nm) freezes. The threshold width of CSH gap that allows the stable existence of ice is 1.5 ± 0.1 nm. A non-icing layer with an average thickness of ∼0.65 nm exists ambient to CSH surface. The main factor affecting the melting point of confined water is the size of the confined space rather than the water filling fraction. The Gibbs-Thomson model is utilized to describe the relationship between the melting temperature and the width of the confined CSH layers. The utilization of this modeling technique presents a novel approach to replicate the freezing process of nanostructures in cementitious composites subjected to low-temperature erosion.

Interaction of layered double hydroxide phases with chloride ions

AbstractFor the sustainable transition of the construction sector, the durability of cementitious materials needs to be guaranteed. This requires a fundamental understanding of the deterioration mechanisms for example how the ingress of potentially detrimental ions affects the composition of the pore solution as well as the phase assemblage. This contribution links results from several research projects investigating the changes in layered double hydroxides (LDH) composition upon exposure to chlorides. The Cl/Al ratio in chloride‐containing AFm phases depends on the chloride concentration as well as on the pH of the liquid phase. In addition, the amount of AFm phases is affected by the pH. Another member of the LDH group, hydrotalcite (Ht), can also incorporate chloride ions into the interlayer and exhibit a similar chloride‐binding capacity as stoichiometric Friedel's salt. However, the chloride‐binding capacity of Ht also depends on the composition of the pore solution. These findings aid the fundamental understanding of chloride‐binding mechanisms of cementitious materials. This is especially important, as the pH and calcium availability in the pore solution of hydrated cement may be altered during its service life. Moreover, the results may help to accurately predict the durability performance of samples in the laboratory.

Atomistic insights into the effect of temperature on capillary transport of water molecules in epoxy-modified calcium silicate hydrate nanopore: diffusion, kinetics, and mechanism

The movement of water molecules at the atomic scale within the calcium silicate hydrate (C–S–H) gel pores serves a dual role: it creates an environment for harmful chemical reactions within the pores and functions as a carrier for the transport of detrimental ions, thereby affects the mechanical properties and durability of cementitious materials. However, direct experimental observation poses substantial challenges. This study offers new insights into how temperature (253 K, 273 K, 293 K, and 313 K) affects the capillary transport of water molecules in epoxy-modified C–S–H. The findings demonstrate that the pore size undergoes continuous changes during immersion due to epoxy clustering or detachment, resulting in three scenarios: narrowing of epoxy/C–S–H channels (253 K, 273 K), channel blockage (293 K), and complete detachment (313 K). Moreover, the interactions between water molecules and epoxy lead to epoxy detachment or cluster formation on the C–S–H surface. As the temperature increases, the interaction between C–S–H and cross-linked epoxy resin weakens. The coordination between C–S–H and epoxy resin decreases, while the coordination with water increases. This paper provides valuable insights into the transport behavior of liquids within the epoxy-modified C–S–H pores of cement-based materials. It contributes to a better understanding of how liquids move and interact within the modified pore structure, which is beneficial for enhancing the performance and properties of cement-based materials.

Deterioration of Cement-Based Materials in Low-Temperature Seawater.

Cementitious materials have potential for infrastructure development in low-temperature marine environments, including in seawater at high latitudes and in deep-sea environments (water depths of >1000 m). Although the marine deterioration of cementitious materials has been widely investigated, the influence of seawater temperature has not been elucidated. In this study, to determine the effects of low-temperature seawater on the durability of cementitious materials, cement paste specimens were immersed in a seawater tank at room temperature and 2 °C for 433 days. The specimen immersed in low-temperature seawater exhibited significant deterioration with a partially collapsed surface, whereas the specimen immersed in room-temperature seawater maintained its original shape. Following low-temperature immersion, Ca dissolution was more pronounced and dissolved portlandite, decalcified calcium (alumino)silicate hydrate (C-(A-)S-H), magnesium (alumino)silicate hydrate (M-(A-)S-H), and thaumasite were observed on the collapsed surface. Such significant deterioration can be attributed to the increased solubility of portlandite under low-temperature conditions, which could promote Ca dissolution and subsequently lead to C-(A-)S-H decalcification and the formation of M-(A-)S-H and thaumasite. These insights are expected to contribute to the successful construction and maintenance of cementitious structures in low-temperature seawater.

Water-soluble polymers in cementitious materials: A comprehensive review of roles, mechanisms and applications

This review paper provides an extensive assessment of the diverse roles played by water-soluble polymers in cementitious materials. It commences with an introduction that provides a thorough overview of the background, objectives and limitations of the review. Subsequently, the various types of water-soluble polymers, encompassing natural, semi-synthetic and synthetic variants, are examined in detail, alongside an exploration of their working mechanisms within cementitious materials. Mechanisms discussed include entanglement and association, adsorption and complexation, as well as bridging. Furthermore, this review delves into the influence of water-soluble polymers on the microstructure, fresh properties, mechanical properties and durability of cementitious materials. A comprehensive analysis of the challenges and opportunities associated with the implementation of water-soluble polymers in cementitious materials is also presented, followed by a summary of the key findings and recommendations for both practical applications and future research endeavors. Overall, this review provides invaluable insights for researchers and practitioners, shedding light on the multifaceted functions of water-soluble polymers in cementitious materials.

Modeling of monolayer water adsorption on surface of cement minerals by molecule simulation and adsorption isotherm

The performance of water on the pore surface governs the mechanical properties and durability of cementitious materials and structures. As a fundamental mechanism, the interaction between water and cementitious mineral micropore surfaces behaves differently under various circumstances, which can be investigated by molecular simulation methods in detail. Molecular simulations based on Grand Canonical Monte Carlo method were performed to obtain the water vapor adsorption isotherms on the surface of tricalcium silicate (C3S) and calcium hydroxide (CH), which are selected as typical cement mineral and hydration product respectively. The adsorption behavior of C3S and CH is compared by the adsorption energy and adsorption isotherm model. The condensation processes were explained by the Kelvin equation. The critical pore sizes of C3S and CH for condensation are 19 Å and 15 Å respectively. Beyond the critical pore size, water adsorption shows monolayer adsorption performance. The water adsorption process on the surface includes three stages: rapid adsorption, stable adsorption and slightly condensed adsorption, which are related to the surface interaction of minerals with water molecules. The Langmuir model is more suitable for the CH with homogeneous surface, while the Freundlich model is more suitable for the C3S model with nonhomogeneous surface. The adsorption heat of the first layer of water film and adsorption energy on the surface of CH are higher.

Development of Pore Pressure in Cementitious Materials under Low Thermal Effects: Evidence from Optimization of Pore Structure by Incorporation of Fly Ash.

Studies on durability of cementitious materials have focused on harsh environments, but less attention has been paid to low thermal loading situations. In this paper, with the aim of exploring the evolution of internal pore pressure and microcrack extension of cementitious under low thermal environment, cement paste specimens with thermal environment slightly below 100 °C and three water-binder ratios (0.4, 0.45 and 0.5) and four fly ash admixtures (0, 10%, 20% and 30%) were designed. Firstly, the internal pore pressure of the cement paste was tested; secondly, the average effective pore pressure of the cement paste was calculated; and finally, the phase field method was used to explore the expansion of microcracks inside the cement paste when the temperature gradually increased. It was found that the internal pore pressure of the paste showed a decreasing trend as the water-binder ratio and fly ash admixture increased, and the numerical simulation found that the sprouting and development of cracks were delayed when 10% fly ash was added to the cement paste, which was consistent with the experimental results. This work provides a basis for the durability development of concrete under low thermal environment.

How nano-bubble water and nano-silica affect the air-voids characteristics and freeze-thaw resistance of air-entrained cementitious materials at low atmospheric pressure?

With more infrastructures being built in plateau regions, low atmospheric pressure is put forward as a new factor affecting the mechanical properties and durability of cementitious materials, but its influence is inconclusive, and the failure of freeze-thaw has not been effectively solved. This research explored the influences of both nano-bubble water (NBW) and nano-silica (NS) on air-voids characteristics and freeze-thaw resistance of cementitious materials formed and cured at different air pressure (0.4P, 0.7P, P; P=1atm); and investigated the effects and its mechanisms of low air pressure on performances of cementitious materials. The air-voids structure analyser, SEM, XRD and TG-DSC were employed to evaluate the microstructure and cement hydration of hardened cement paste samples. Results show that low-pressure samples have abnormal air-void parameters and poor bubble stability, which lead to a decrease in freeze-thaw resistance. It is proved that both NBW and NS can improve the freeze-thaw resistance and mechanical strength of samples at low atmospheric pressure by accelerating cement hydration, enhancing bubble stability, and optimizing air-voids parameters. The mechanisms of low pressure, NBW and NS on properties of cementitious materials are expounded. This research proposes new perspectives for improving the durability of air-entrained cementitious materials in plateau and enables us to further comprehend the effects and principles of low air pressure on performances of cementitious materials.

Degradation of thermal stability and micromechanical properties of the C-S-H phase induced by ultra-confined water at elevated temperatures.

Water in the nanometer to micrometer-sized pores of calcium silicate hydrate (C-S-H) is essential for the binding process of cementitious materials. The quantity, location, and physical state of water in C-S-H pores under extreme conditions significantly influence the strength and durability of cementitious materials. The present study employed ReaxFF and molecular dynamics (MD) simulation to evaluate the effects of water ultra-confined in the nanopores on the structure, bonds, dynamics, and tensile mechanism of the C-S-H grains at elevated temperatures. The results indicate that the temperature elevation may interfere with the water molecule's hydrogen-bond network between the C-S-H grains, causing a notable nanometer-scale pore expansion. Simultaneously, the diffusion coefficient of water molecules confined in nanopores gradually increased, and their dynamic characteristics shifted from a glassy nature to free water. Additionally, high temperatures promoted hydrolysis reactions and the breakage of chemical bonds in the C-S-H framework, causing disintegration of the silicate skeleton and a decrease in the mechanical attributes of C-S-H. Moreover, the uniaxial tensile test at high temperatures revealed that the silicate chain groups in the C-S-H substrates underwent thermal curling. In contrast to interlayer-bound water, under the action of tension, water molecules in nanopores are viscous, forming water layers.

Durability Improvement of Cement Using Amphiphilic Calcium Carbonate Nanoparticles

The durability of cementitious materials is significant concerning long-term performance. Nanomaterials are promising candidates for deep refinement of cement durability. Hydrophobic calcium carbonate is a widely applied and easily accessible nanomaterial. However, its hydrophobicity and poor dispersity in water prohibit its direct application in cementitious materials. In this study, hydrophobic calcium carbonate nanoparticles (HbCC) were modified using a novel amphiphilic comb-shaped dispersant that is capable of laurinol release. The modification was conducted to improve the dispersity of HbCC and their compatibility with hydration products. The dispersion-improved calcium carbonate particles (AmphCC) were characterized and tested for cement durability improvement performance. According to the results, the AmphCC particles showed a pronounced effect on improving permeation resistance of cement mortars, with water absorption and chloride penetration considerably lowered. Moreover, the introduction of AmphCC in cement did not show significant adverse effects on strength development. Compared with AmphCC, a single addition of the unmodified HbCC and the dispersant cannot achieve equivalent effects. The superior effect of AmphCC is due to the synergistic effect of good particle dispersion and controlled release of the hydrophobic molecules, which is achieved by dispersion of HbCC with binding of the dispersant.

A numerical chemo-micromechanical damage model of sulfate attack in cementitious materials

The sulfate attack (SA) of cementitious materials widely exists, which severely reduces the mechanical properties and durability of cementitious materials. However, few numerical SA damage models of cementitious materials have been comprehensively developed. The understanding and simulation of the chemo-mechanical behavior of cementitious materials are beneficial to better modeling, predictions and designs of underground structures. In this research, a numerical chemo-micromechanical damage model under the SA and loading is proposed to explore the cracking process of the cementitious materials based on the discrete element method (DEM). Some inherent characteristics of the chemical attack can be well considered in the proposed numerical model. The local damage effect can be simulated, as well as the sulfate corrosion degree and the material component. The performance of this proposed model is confirmed and validated by available experimental results. We examine the dependence of the strength and the elastic moduli of the cementitious material on: (a) the content of ettringite, (b) the distribution of ettringite, (c) the mechanical properties of the cementitious matrix, (d) the void ratio of the cementitious materials, (e) the confining pressure, and (f) the expansion coefficient of sulfate corrosion products. The softening and fluctuating phenomena are witnessed in the stress-strain curves. The failure mode of cementitious materials with the SA is different from that of specimens without the SA. The damage parameters of cementitious materials under the SA are examined in depth. The numerical results reveal that the proposed damage model is feasible and valuable in the modeling, predictions, applications and durability of chemo-mechanical sulfate attack problems in cementitious materials.

Quantitative assessment of microstructural changes of hydrated cement blends due to leaching and carbonation, based on statistical analysis of image data

The evolution of the microstructure in corrosive environments plays a key role for the performance and durability of cementitious materials, however, appropriate methods to quantitatively describe microstructural alterations are limited. Here, statistical analysis of microscopic data is used to describe changes in porosity, continuous and individual pore size distributions of reactive cement phases during leaching and carbonation of hydrated cement blends. Therefore, BSE images obtained from (un)damaged areas of the cement blends were segmented using image processing techniques, followed by geometrical characterization and quantitative evaluation of the microstructural response(s). It is shown that the dissolution of portlandite generates a high meso- and macro-porosity (> 100-4000 nm pores), whereas precipitation of C-(A)-S-H and Ca-carbonate polymorphs leads to a densification of the microstructure, i.e., reducing the fine meso- and micro-porosity (< 500 nm pores). Cement blends made with hydraulically active SCMs and chemically poorly reactive carbonate fillers performed better than pure (OPC-based) cement paste.

CemGEMS – an easy-to-use web application for thermodynamic modeling of cementitious materials

Thermodynamic equilibrium calculations for cementitious materials enable predictions of stable phases and solution composition. In the last two decades, thermodynamic modelling has been increasingly used to understand the impact of factors such as cement composition, hydration, leaching, or temperature on the phases and properties of a hydrated cementitious system. General thermodynamic modelling codes such as GEM-Selektor have versatile but complex user interfaces requiring a considerable learning and training time. Hence there is a need for a dedicated tool, easy to learn and to use, with little to no maintenance efforts. CemGEMS (https://cemgems.app) is a free-to-use web app developed to meet this need, i.e. to assist cement chemists, students and industrial engineers in easily performing and visualizing thermodynamic simulations of hydration of cementitious materials at temperatures 0-99 °C and pressures 1-100 bar. At the server side, CemGEMS runs the GEMS code (https://gems.web.psi.ch) using the PSI/Nagra and Cemdata18 chemical thermodynamic data-bases (https://www.empa.ch/cemdata).&#x0D; The present paper summarizes the concepts of CemGEMS and its template data, highlights unique features of value for cement chemists that are not available in other tools, presents several calculated examples related to hydration and durability of cementitious materials, and compares the results with thermodynamic modelling using the desktop GEM-Selektor code.

Evaluation of self-healing performance of a smart composite material (SMA-ECC)

The durability of cementitious materials is affected by the presence of cracks. This paper proposed a novel composite material and evaluated its crack healing ability. This material consisted with engineered cementitious composite (ECC) and shape memory alloy (SMA) fibers. A total of 12 specimens were made and tested under flexural loads. Test parameters included material type and target displacement level. Test results indicated that specimens with SMA-ECC had great increase in strength and ductility compared with specimens with concrete. Specimens with SMA-ECC exhibited promising crack healing ability by effectively reducing the crack number and width. The self-healing ability reduced with increasing target displacement level. The self-healing ability was further investigated through ultrasonic pulse test. Ultrasonic pulse test results were consistent with the mechanical test results, indicating effectiveness of this test method. This composite material SMA-ECC has promising application in infrastructure critical for security to mitigate damage and heal cracks, and increases durability of the structure, and reduces maintenance cost.

Modified self-healing cementitious materials based on epoxy and calcium nitrate microencapsulation

Aim This study was conducted to utilise the effective self-healing system to regain the mechanical properties of the cementitious materials containing micro-cracks. Methods Storing epoxy and calcium nitrate as healing agents was performed by microencapsulation in the urea–formaldehyde shell. The microcapsules were characterised by Fourier transform infrared, thermogravimetric analysis, differential scanning calorimetric, field emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. Cementitious samples were prepared by mortar mixing with various amounts of microcapsules (0, 1, 3 and 6% w/w). The healing potential of microcapsules was analysed based on the recovery rate of the mechanical properties. Results The obtained microcapsules have an outer rough surface, suitable diameter (1–100 μm) and shell thickness (0.2–0.6 µm), and remarkable thermal stability (up to 260 °C). Mechanical test results exhibit that created micro-cracks were healed completely and regained the recovery rates over 100%. Conclusion The prepared microcapsules besides enhancing thermal stability, demonstrate a high performance in microcracks sealing to improve durability of cementitious materials.

Monitoring the Setting Process of Cementitious Materials Using Guided Waves in Thin Rods.

Characterizing early-age properties is very important for the quality control and durability of cementitious materials. In this paper, an approach using embedded guided waves was adopted to monitor the changes in the mechanical proprieties of mortar and concrete during setting, and embedded thin rods with low-cost piezoelectric sensors mounted on top were used for guide wave monitoring. Through continuous attenuation monitoring of the guided waves, the evolution of mortar and concrete properties was characterized. Four different kinds of metallic rods were tested at the same time to find out the optimal setup. Meanwhile, shear wave velocities of the mortar and concrete samples were monitored and correlated to the attenuation, and setting time tests were also performed on these samples. Experimental results demonstrate that the proposed approach could monitor the evolution of the setting of cementitious materials quantitatively, and time of the initial setting could be determined by this technique as well. In addition, it is found that the attenuations of fundamental longitudinal guided wave mode are almost the same in concrete samples and mortar samples sieved from concrete, indicating that this technique is able to eliminate the effects of coarse aggregates, which makes it of great potential for in-situ monitoring of early age concrete.

A Review on the Application of Nanocellulose in Cementitious Materials.

The development of the concrete industry is always accompanied by some environmental issues such as global warming and energy consumption. Under this circumstance, the application of nanocellulose in cementitious materials is attracting more and more attention in recent years not only because of its renewability and sustainability but also because of its unique properties. To trace the research progress and provide some guidance for future research, the application of nanocellulose to cementitious materials is reviewed. Specifically, the effects of cellulose nanocrystal (CNC), cellulose nanofibril (CNF), bacterial cellulose (BC), and cellulose filament (CF) on the physical and fresh properties, hydration, mechanical properties, microstructure, rheology, shrinkage, and durability of cementitious materials are summarized. It can be seen that the type, dosage, and dispersion of nanocellulose, and even the cementitious matrix type can lead to different results. Moreover, in this review, some unexplored topics are highlighted and remain to be further studied. Lastly, the major challenge of nanocellulose dispersion, related to the effectiveness of nanocellulose in cementitious materials, is examined in detail.

Effects of pH on the nano/micro structure of calcium silicate hydrate (C-S-H) under sulfate attack

Calcium silicate hydrate (C-S-H), the most important Portland cement hydration product, determines the mechanical properties and durability of cementitious materials. In marine environment, C-S-H often suffers from sulfate attack – one of the most common and severe degradations for concrete. pH is considered as a critical factor in determining the deterioration behavior of C-S-H during sulfate attack, of which the significance may be overlooked. This study focused on the role of pH on the deterioration of C-S-H in terms of the composition and nano/micro structure under sulfate attack. The results show that lowering pH aggravates the decalcification of C-S-H, whereas a strong alkaline condition is beneficial to increase the resistance to deterioration. An increase in the mean chain length together with the proportion of large pores (>10 nm) is observed when C-S-H is subjected to low-pH sulfate attack (pH = 10–12), resulting in a relatively loose structure. The deep analysis on defective tobermorite model reveals that calcium at the interlayer of C-S-H nanostructure is readily removed under sulfate attack, thereby improving the potential of Si-O-Si groups formation and increases the mean chain length of C-S-H.

Advances of graphene- and graphene oxide-modified cementitious materials

Abstract Emerging nanomaterials provide an invaluable opportunity for the development of cementitious materials. Many scholars have explored the influence of graphene (GP) and graphene oxide (GO) on the performance of the cementitious materials. This article reviews the previous research on the effect of GP and GO on the properties of cementitious materials. Detailed review of the mechanical properties and durability of cementitious materials containing GP or GO nanofilms is presented, and the mechanism is discussed. The mechanical properties of GO-cementitious materials are significantly enhanced. The optimal improvement of GO-modified compressive, flexural, and tensile strengths is 77.3%, 78.3%, and 78.6%, respectively. The durability of GO- and GP-modified cementitious material is compared with the control group. The incorporation of GP or GO significantly improves the sulfate attack resistance, and the transport properties can be decreased, while the frost resistance of GO- and GP-modified cementitious materials needs further research. This literature review shows that the microstructure of GO- and GP-modified cementitious material is improved in three aspects: accelerating the cement hydration, refining the pore structure, and hindering the crack propagation.

Investigation on parameters optimization for gas permeability testing of concrete: Inlet-gas pressure and confining pressure

Permeability is an important characteristic associated with the durability of cementitious materials. Gas permeability testing could overcome some shortcomings of traditional methods but its key parameters have so far not been identified for long periods, reducing comparability of test results. In this study, coarse-aggregate settlement in concrete was taken into consideration by dividing concrete cores into smaller segments and the gas-permeability of concrete specimens was measured by the modified CemBureau method. Apparent gas-permeability (Ka) values of the segments were determined under multiple inlet-gas pressures (1.0 bar–40.0 bar) and various confining-pressures (30 bar–90 bar), which then were applied to calculate the intrinsic permeability (Kint) values and Klinkenberg coefficient (βk) to obtain optimal parameters of inlet-gas pressure and confining-pressure. Meanwhile, X-ray computed tomography (X-ray CT), mercury intrusion porosimetry method (MIP) and specific gravity method (SG) were used for auxiliary calibration of test parameters. The results showed that four zones with different inlet-gas pressures were observed for apparent gas-permeability: unstable zone, metastable zone, stable zone, and anamorphic zone. Combined with gas-permeability, pore characteristics were employed for auxiliary calibration of parameter optimization. In sum, 15.0 bar–30.0 bar inlet-gas pressure and 50 bar confining-pressure were determined as the best parameters for concrete gas-permeability testing.