Microstructure Of Cement Paste Research Articles

Relationship Between Expansion and Strength of Cement Paste with CaO-Based Expansive Agent.

In order to explore the intrinsic relationship between the expansion and strength of cementitious materials with CaO-based expansion agent (CEA), the effects of CEA on the expansion rate, strength, microstructure, and hydration products of cement paste were studied. The interaction mechanism between the expansion rate and compressive strength of cement paste with CEA was discussed. The results show that the addition of CEA increases the expansion rate, porosity, and hydration degree of cement paste while reducing the compactness and compressive strength of cement paste. As the CEA dosage increases, the expansion rate of cement paste gradually increases. During the expansion of cement paste, microcracks may occur. The larger the expansion rate, the more microcracks there are, and the compressive strength decreases linearly with the increase in the expansion rate. When the CEA dosage is the same, the expansion rate of cement paste gradually increases with the increase of mineral admixture content, and the expansion rate decreases linearly with the increase of compressive strength.

Influence of water-repellent admixtures ( Sitren and Stearate materials) on the microstructure and mechanical performance of conventional Portland cement paste and mortar

The longevity of mortar and concrete structures can be compromised by the absorption of water and other fluids, leading to deterioration and aesthetic issues. To address this, water-repellent admixtures are employed to enhance the service life of mortar and concrete components by improving their mechanical and microstructural characteristics. This study focus on the effects of incorporating Sitren P 750 and various stearate materials (calcium, zinc, aluminum, and barium) as admixtures with ordinary Portland cement at mortar and paste dosages of 0.5%, 1.0%, and 1.5% of the cement content. We found that mortars with water-repellent admixtures exhibited competitive mechanical properties at all curing ages. Additionally, the study confirmed the contribution of these admixtures to the production of hydration products and the structural development of the mortars, as investigated through scanning electron microscopy, thermogravimetric–derivative thermogravimetric, and X-ray diffraction analyses. Despite alterations in several physical properties and hydration kinetics due to the water-repellent compounds and their dosages, all admixtures provided effective water-repellent protection. This was further corroborated by water contact angle tests and the measurement of the capillary water absorption coefficient for all samples. Identifying the optimal mixture ratio for construction technology and effectively incorporating repellence features is a crucial aspect of this research.

Study on the effect of nano-silica on the early-age strength and microstructure of cement paste mixed with calcium nitrite under negative temperature conditions

During construction at low temperatures, fresh concrete is susceptible to early freeze damage, which can permanently damage the concrete structure. Therefore, this study aimed to enhance the early-age strength and durability properties of the cement paste at −5 ℃ by incorporating calcium nitrite (CN) antifreeze and nano-silica (NS). First, the effects of CN and NS on the fresh properties of the cement paste were measured by setting time and bleeding rate tests. Subsequently, the mechanical properties and chloride content after salt solution erosion were tested for each group of specimens, and the change in slurry densification was further observed by ultrasonic pulse velocity and resistivity tests. Finally, the hydration products and microstructure of the specimens were analyzed using XRD and SEM tests. The results showed that the addition of CN and NS could reduce the setting time of cement paste and avoid the bleeding phenomenon of cement paste under negative temperature environment. The decrease in curing temperature and the use of NS both inhibited the promotion of C3A hydration by nitrite ions, which led to a decrease in nitrite-AFm content. However, NS can compensate for the reduced nitrite-AFm content by promoting the production of hydrated C-S-H through nucleation and pozzolanic effects. Ultimately, the strength and resistance of the slurry to chloride erosion are improved.

Green synthesis of graphene oxide from invasive plant species (Nymphaeaceae) for enhancing cement paste microstructure and compressive strength

The proliferation of invasive species, particularly water lilies (Nymphaeaceae), in aquatic ecosystems, such as Dal Lake in Srinagar, J&K, India, has led to significant challenges for aquatic life. This research addresses this issue by harnessing the invasive water lily as a resource for an environmentally conscious approach to produce graphene oxide (GO) through thermal pyrolysis. The synthesized GO was incorporated into cement paste (CP) (ranging from 0 to 0.09 wt%) to explore its impact on workability, mechanical properties, and microstructure. Increasing GO concentrations led to decreased workability. However, GO positively influenced compressive strength, with optimal enhancements observed at 0.06 %, a maximum enhancement in compressive strength of 53.7 % and 35.4 % at 7 and 28 days when compared to the control CP. Microstructure analysis through FE-SEM revealed improved cement hydration, pore filling, and densified microstructure, supported by XRD and FT-IR findings. Specifically, GO at 0.06 % concentration showed notable improvements, indicating its crucial role in enhancing mechanical properties.

A novel mesh algorithm to improve the packing efficiency of irregular-shaped particles in simulating cement paste's microstructure

Irregular-shaped particle packing is important to simulate the cement paste microstructure. However, the efficiency of current packing models is relatively low. This study proposes a novel packing algorithm named the Mesh Optimization Packing (MOP) model inspired by the VOX and extent overlap box (EOB) methods. The MOP model's performance in terms of accuracy, uniformity, and randomness were evaluated. Meanwhile, compared to the Anm model 2.0 and the VOX model, the MOP model excels in simulating the initial microstructure of cement paste with high cement volume fractions. When the cement volume fraction is 56.03 %, the VOX model requires 124.68 h, while the MOP model only takes 18.80 h. By adding uniform-thickness shells to irregular-shaped particles, the MOP model integrates with the HYMOSTRUC3D-E model to simulate the evolution and uniaxial stretching process of the cement paste microstructure. This innovative modelling approach offers a promising solution for future simulations of cement paste microstructure.

Micromechanics and microstructure based machine learning approach: Unveiling the role of porosity and hydrated phases on the tensile behaviour of cement pastes

The fracture process and the mechanical performance of the cement paste rely significantly on its tensile behaviour. Machine learning methods have been recently developed to predict this behaviour based on numerous experimental measurements. Due to multi-phase heterogeneous nature of cement paste microstructure, evaluation of the role of each chemical phase on the cracking of cement paste is necessary to develop optimized binder systems. Numerous experimental tests would be necessary to determine the best cement pastes in a considered environment. Therefore, in this study, a hybrid approach based on an ensemble machine learning model and a microstructure informed micromechanical model is proposed for predicting the tensile behaviour of hydrated cement pastes. The model can be used as a quick prediction tool for tensile strength of a given microstructure or for deep analysis on the optimization of binder system. A Deep Neural Networks (DNN) model was developed by training and validating a large dataset detailing the chemical phase composition, phase volume fractions and the tensile strength of the cement pastes. This dataset covers an extensive range of Portland cements, hydration ages and water-to-cement ratios. It was developed by simulating cement thermodynamics and tensile behaviour using a damage micromechanical model; which is otherwise almost impossible to obtain through experimental means. Additionally, two generative algorithms, tabular generative adversial networks (TGAN) and conditional generative adversial networks (CTGAN), were employed for dataset augmentation as a sampling method for the sensitivity analysis. This machine learning study provides an in-depth investigation to identify the role of volume fraction of solid phases (C-S-H, ettringite, portlandite and hydrogarnet) and micro porosity (dry and filled) in affecting the tensile behaviour of hydrated cement paste. Optimization assessment of the microstructure was then performed using micromechanical analysis and damage propagation in hydrated cement paste phases and porous network.

Effect of admixed silicone emulsion on water and chloride transport properties of concrete

The addition of silicone is effective method for improving both surface and internal hydrophobicity of concrete, thus clarifying its effect on transport property of concrete is very important. In this study, both water and chloride transport properties of concrete incorporated with three silicone emulsions based on different active ingredients (silane oligomers or silane monomers) were evaluated and investigated. The results show that all three silicone emulsions exhibit no obvious negative effect on hydration and microstructure of cement paste; however, the admixed silicone emulsions increase both the thickness and porosity of ITZ in concrete. Therefore, the admixed silicone emulsions result in reduced compressive strength of concrete. Further, the incorporated silicone emulsions efficiently increase surface and internal water contact angle of concrete, thus mitigating both water absorption and chloride transport in concrete. Due to more pronounced interaction between silane oligomers and hydration products based on molecular dynamics simulation, the beneficial effect on improving hydrophobicity of concrete and halting water and chloride transport is more significant for the admixed silicone emulsion with silane oligomers as active ingredient.

A closed-loop recycling of wastewater derived from aqueous carbonation of basic oxygen furnace slag in cement paste production

Aqueous carbonation (AC) treatment is a promising method for enhancing the cementitious activity of Ca- and Mg-rich solid wastes, such as basic oxygen furnace slag (BOFS), while also reducing carbon emissions. However, the carbonated filtrate (CF) solution generated during the AC process poses significant environmental challenges and limits its large-scale application. This paper, therefore, explores the feasibility of recycling CF in cement paste production as a strategy for managing AC wastewater. The study examines the impact of CF on the physico-mechanical properties, hydration behavior and microstructure of cement pastes (pure and blended with either 10% as-received or carbonated BOFS), compared to those prepared with tap water (TW) and carbonated water (CW). The results indicate that carbonated solutions (CF and CW) promote the hydration of aluminate phase in cement, with a more pronounced effect observed for CW. The solid suspensions in CF, particularly nesquehonite, restrict the growth space for calcium silicate hydrates (C-S-H) in the paste matrix, resulting in the formation of foil-like Type II C-S-H and lowering compressive strength. However, the additional nucleation sites provided by calcite crystals in carbonated BOFS (C-BOFS) accelerate cement hydration in CF-based pastes and mitigate strength loss by promoting the formation of more fibrillary C-S-H. Furthermore, the addition of a superplasticizer reduces interparticle forces in the C-BOFS-CF paste, further enhancing strength development and achieving a 28-day strength comparable to that of the control sample (OPC-TW paste).

Effect of chelator on carbon sequestration and mechanical properties of CO2-cured cement pastes with different pore structures

Chelator can accelerate the mineralization reaction of cement-based materials, playing a positive role in reducing CO2 emissions into the atmosphere. Cement pastes with different pore structures were prepared by adjusting the water cement ratio, and effects of chelator on the microstructure, phase composition, carbon sequestration and mechanical properties of CO2-cured cement pastes with different pore structures were investigated in this study. The results indicated that chelator could promote CO2 transport in dense cement paste with more gel pore and transition pore and medium dense cement paste with many transition pore and capillary pore, and induce mineralization reaction to repair larger pores in loose cement paste with more capillary pore and megalopore (LCM). Chelator had the most significant effect on improving the performance of cement paste of LCM, increasing the carbonation sequestration rate and compressive strength of cement paste cured for 48 h by 19.0 % and 28.1 %, respectively.

Influence of Curing Humidity on the Strength and Microstructure of Cement Paste Incorporating Metakaolin and Limestone

Influence of Curing Humidity on the Strength and Microstructure of Cement Paste Incorporating Metakaolin and Limestone

The influence of sugarcane bagasse ash on the microstructure of autoclaved cementitious material: Comparative study with amorphous and crystalline silica

This study aimed to investigate the effects of a partial replacement (25 wt%) of Portland cement with sugarcane bagasse ash (SCBA) on the microstructure of cement pastes. The effects were compared with those of pastes containing amorphous (silica fume) or crystalline (crushed quartz) silica. Two curing methods were used for the pastes: conventional curing (25 °C and RH > 95%) and autoclave curing (220 °C under 2.1 MPa for 8 h). The microstructure of the pastes was characterized by XRD, SEM, FTIR, and the hardness and elastic modulus of their C–S–H regions. The results showed that the pastes cured at room temperature exhibited similar microstructure development, showing little or no reaction, even though silica fume is a highly reactive pozzolanic material. Differently, the hardness of the pastes containing silica fume, SBCA and crushed quartz replacement for cement increased approximately threefold after autoclave curing, while, in contrast, the reference sample, no cement replacement, showed no improvement. This is attributed to the formation of tobermorite and xonotlite. The presence of Al in the SCBA allowed the formation of tobermorite under the autoclave curing conditions (220 °C, 2.1 MPa for 8 h), and in this case, the SCBA exhibited behavior between silica fume and fine quartz.

Microstructure analysis of cement-biochar composites

The use of biochar as a concrete constituent has been proposed to reduce the massive carbon footprint of concrete. Due to the low density and complex porosity of biochar, microstructural analysis of Portland cement-biochar composites is challenging. This causes challenges to the improvement of the micro-scale understanding of biochar composite behavior. This work advances the microstructural understanding of Portland cement composites with 0, 5, and 25 volume percent (vol%) of cement replaced with wood biochar by applying common characterization techniques of mercury intrusion porosimetry (MIP), gas sorption, scanning electron microscopy, and isothermal heat flow calorimetry (HFC) in conjunction with 1H nuclear magnetic resonance (NMR) and micro-X-ray computed tomography (XCT) analysis techniques. The combination of these techniques allows a multi-scale investigation of the effect of biochar on the microstructure of cement paste. NMR and XCT techniques allow the observation and quantification of the pore space. HFC and MIP confirmed that biochar absorbs moisture and reduces the effective water-cement ratio. Gas sorption, MIP, and NMR shows that 5 vol% replacement does not significantly affect the gel and capillary pore structures. Results from XCT (supported by MIP and NMR) show that biochar can reduce the formation of larger pores. Importantly, XCT results suggest that biochar can act as a flaw in the microstructure which could explain reductions in the mechanical properties. Overall, the mechanical properties already analyzed in the literature are consistent with the microstructural changes observed, and these results highlight the need to carefully tailor the volume fraction of biochar to control its effect on the paste microstructure.

Study on the Modification Mechanism of Soap-Free Latex on the Microstructure and Mechanical Properties of Cement Paste

Abstract In view of problems such as the decline in strength of cement paste and latex exudation caused by the addition of conventional latex, JAS soap-free latex (JAS latex) was prepared by soap-free emulsion polymerization technology. JAS latex had the characteristics of low viscosity, uniform particle size, good dispersity of particles, and good compatibility with cement admixtures. JAS latex had little impact on the fluidity of oil-well cement paste. The free liquid of the cement paste with 10 % JAS latex was 0 %, and its liquid-loss content was 43 mL. When the JAS cement paste was cured at 90°C, its compressive strength was 34.08 MPa. When the curing temperature was 70°C, the bond strength between the paste and metal casing reached 4.95 MPa. Combining the results tested by X-ray diffraction, scanning electron microscopy, and atomic force microscopy showed that JAS latex did not affect the hydration process of oil-well cement, had good film-forming ability in cement paste, and improved the density and impact resistance of the cement paste. It is helpful to improve the sealing integrity and sealing ability of cement sheath in cementing engineering and ensure the safe and efficient development of oil and natural gas resources.

Bond behaviour between steel fibre and cement mortar exposed to elevated temperature

In order to accurately evaluate the deterioration of the mechanical properties of concrete reinforced with steel fibre (SF) after exposure to elevated temperature, it is particularly important to study the bonding properties between the SF and the concrete matrix. In this work, four types of SFs and five cement mortars with different strengths were used to investigate the bond behaviour of the SF–mortar interface after exposure to elevated temperature. The results showed that the compressive and flexural strengths of each mortar decreased significantly after elevated temperature treatment, and the attenuation degree of flexural strength was greater than that of the compressive strength. In addition, the ultimate pull-out load of specimens with straight SFs gradually decreased with an increase in exposure temperature. However, the ultimate pull-out load of specimens with hooked-end SFs showed no significant change between exposures to 20°C and 400°C. When the exposure temperature exceeded 400°C, the ultimate pull-out load gradually decreased with an increase in temperature. The damage mechanism of the SF–mortar interface under elevated temperature was investigated by analysing the interfacial microstructure and phase change of cement pastes. Finally, a formula to related the ultimate bond strength with temperature was established.

Effect of ground granulated blast-furnace slag (GGBS) and sulphoaluminate cement (SAC) on the strength and microstructure of ordinary Portland cement paste at elevated temperatures

This study explored the potential of GGBS and SAC to enhance the thermal resistance of cement. The research explores changes in compressive strength and pore structure at various temperatures, employing microscopic analysis to elucidate underlying mechanisms. The results indicated that an optimal GGBS content enhanced strength, whereas SAC significantly reduced strength. The strength variation was not correlated with porosity or pore size distribution but rather with the hydration products of the blended cement. GGBS promoted the generation of C-A-S-H gels by introducing Al to replace Si in C-S-H gels, thereby increasing both the quality and quantity of gels. This enhancement suggested that GGBS improved thermal resistance by augmenting hydrate formation. SAC promoted ettringite formation even at high temperatures but reduced the quantity of hydrate gels, illustrating that SAC did not provide Al for the generation of C-A-S-H gels, consequently diminishing strength.

Mechanism of recalcification and its effects on the microstructure and transport properties of cement paste

Calcium leaching involves the removal of calcium ions from the pore solution and hydration products, leading to a decrease in pH, coarsening of pore structure, and, in severe cases, loss of cohesion, shrinkage, and cracking. Recalcification is a restoration process aiming at repairing degraded C-S-H structures by externally supplying calcium ions. However, our understanding of recalcification mechanism, its potential to reverse calcium leaching, and its effects on deteriorated cementitious matrices remains limited. This study aims at enhancing the understanding of the impact of recalcification on calcium leached cement pastes. Our findings demonstrate that calcium leaching can be partially reversed by immersion in a saturated calcium hydroxide solution. Recalcification functions by introducing calcium ions to the degraded matrix, triggering a reaction with the degraded C-S-H. This process reverses silicate polymerization, increases the Ca/Si ratio in the degraded zone’s, and densifies the pore structure. After only 14 days of recalcification, the degraded portion experienced a 50 % reduction in porosity, an increase in pH. By day 28, recalcification halved the permeability of the treated sample and completely consumed all silica gel. Additionally, our findings reveal that higher temperatures adversely affect the structure of C-S-H, hindering the beneficial structural modifications facilitated by recalcification.

Effect of nano-silica on mechanical properties and microstructure of high-volume ground granulated blast furnace slag cement paste

Effect of nano-silica on mechanical properties and microstructure of high-volume ground granulated blast furnace slag cement paste

Mechanical property evaluation of 3D multi-phase cement paste microstructures reconstructed using generative adversarial networks

This study proposes an artificial intelligence based framework for reconstructing the 3D multi-phase cement paste microstructure to evaluate its mechanical properties using simulation. The reconstruction of cement paste microstructures is performed using modified generative adversarial networks (GANs) based on microstructural images from micro-CT. For computational efficiency, 2D microstructures are first reconstructed and then extended to 3D microstructures. The reconstructed microstructures exhibit the same microstructural features as the original microstructures when characterized by probability functions. Mechanical properties such as stiffness and tensile strength are evaluated for the original and reconstructed specimens using a phase-field fracture model, and similar behaviors are observed. The results confirm that the reconstructed virtual microstructures can be used to supplement the real microstructures in evaluating the mechanical properties of 3D multi-phase cement paste. This approach thus provides a critical element of a data-driven approach to correlating its microstructure and properties.

Research on the effect of different content of rice husk ash on the microstructure of concrete

Mercury injection porosimetry test is used to study the microstructure of rice husk ash cement paste with different content. The influence of rice husk ash on the microstructure of cement paste is analyzed through porosity, pore size distribution, the most probable pore size, pore size gradation and critical pore size analysis. The results show that with the increase of rice husk ash content, the porosity of cement paste decreases, and the pore size distribution and the most probable pore size decrease, which indicates that the addition of rice husk ash can improve the pore structure of concrete and improve the durability of concrete. With the increase of rice husk ash content, the number of harmful holes of cement paste decreases, the number of harmless holes increases, and the critical pore diameter decreases, which indicates that the addition of rice husk ash can improve the strength and impermeability of concrete.

Preparation and properties of porous rice husk ash for internal curing of high performance cement pastes

To address the challenges posed by significant autogenous shrinkage in high-performance concrete and mitigate the adverse effects of conventional internal curing materials on its mechanical properties, this study explored the potential use of rice husk ash (RHA) as internal curing materials. The research investigated the impact of combustion regime (combustion temperature and dwelling time) and the milling process on the microstructure and physical-chemical properties of RHA. Moreover, the effect of RHA on autogenous shrinkage, compressive strength, and microstructure in cement pastes were also reported. Experimental results demonstrated that the combustion regime and milling time could significantly affect the pore structure, particle size and pozzolanic activity of RHA. RHA had good potential for internal curing when it was burned at 600°C for 1 h and milled for 15–30 min. RHA released the entrained water after 12 h to slow down the depletion of free water, and thus inhibited the development of self-drying and autogenous shrinkage. The 168 h shrinkage was reduced by 56.8 %, 62 %, and 51.8 %, respectively when the milling time increased to 30 min. Moreover, the addition of RHA with a smaller particle size could refine the microstructure of matrix and enhance the compressive strength due to its higher pozzolanic activity. These findings suggest promising applications for RHA as an effective internal curing material in high-performance cementitious materials.