Microstructure Of Paste Research Articles

Engineering characteristics of one-part alkali-activated slag-based paste incorporating nano-silica and calcined oyster shells ash

ABSTRACT This study investigates the influence of nano-silica up to 5% by mass on the hydration, engineering properties, and microstructure of one-part alkali-activated slag-based paste with up to 20% calcined oyster shell ash (COSA). Adding nano-silica reduced workability and accelerated setting times. A mixture with 3% nano-silica and 20% COSA showed a 31.55% increase in compressive strength, improved thermal conductivity from 0.434 W/(m · K) to 0.715 W/(m · K), and reduced water absorption from 10.43% to 3.02% when compared to those mixtures with only COSA. These improvements are due to nano-silica interacting with calcium hydroxide, forming hydration products such as ettringite and C-S-H gel, which fill micropores and strengthen the microstructure. This rapid hydration and strength development make it ideal for precast manufacturing. Thus, incorporating nano-silica allows efficient use of up to 20% COSA, making it a sustainable and eco-friendly construction material.

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.

Silicon carbide nanowire-reinforced micro-Ag joint based on pinning effect for power electronics packaging

Low-temperature sintering Ag technology is a feasible approach employed in power electron devices. In this study, the influence of the different amounts (0, 0.03, 0.05, 0.07, 0.10, 0.20 wt%) of silicon carbide nanowires (SiC NWs) on the properties and microstructure of micro-Ag paste sintered at 250 °C without pressure has been investigated. The results exhibit that the bonding strength of the Ag-SiC joint reaches a maximum of 43.57 MPa after doping 0.07 wt% SiC NWs, with an increase of 13 % compared with pure Ag joint. This enhancement mechanism can be owed to the Orowan mechanism and the pinning effect of SiC NWs, which nail at grain boundaries that will restrain the dislocation motion of Ag grains. Meanwhile, the electrical resistivity of Ag-0.07SiC shows a minimum value of 5.20 μΩ cm, approximately 10.65 % lower than pure Ag joint. This is attributed to the well-sintered Ag network and the bridging effect of SiC NWs distributed in Ag particles. Thus, incorporating appropriate content of SiC NWs into micro-Ag paste can strengthen the mechanical performance and electrical conductivity of sintered Ag joint. It is hoped that this research could develop a new micro-Ag paste with outstanding properties that could be employed in high-power electronic devices.

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.

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

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.

Internal hydrophobic treatment for mortar containing supplementary cementitious materials: thermal analysis of kinetics and products of hydration

AbstractThe presented research investigates the application of the organosilicon admixtures based on triethoxyoctylsilane (OTES) on the hydration of the cement-based material with addition of supplementary cementitious materials (SCM) such as blast furnace slag and microsilica. The influence of silane-based admixtures on the kinetics of hydration was investigated by isothermal calorimetry. The calorimetric results disclosed that applied admixtures affect the hydration process of cement paste with SCM. The DTA/TG analysis provided the information about impact of triethoxyoctylsilane on the composition and formation of the mineral phases. The DTA/TG measurements showed noticeable changes in the thermal decomposition of the tested materials and amount of bounded water. The impact of OTES on the microstructure and pore size distribution of pastes was examined by mercury intrusion porosimetry. The result showed significant changes in the range of pore diameters. The influence of organosilicon admixtures on the compressive strength of mortars after 2, 7, 28, 56 and 90 days was also investigated. The effect depended on the mineral additive used. In case of blast furnace slag, the development of compressive strength was only delayed, however, in the case of microsilica, it was stopped.

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.

Influence of Early Hydration Process on the Hydrostatic Pressure Change of Cement Pastes at Different Temperatures.

In cementing operations, a rapid decrease in the hydrostatic pressure of cement paste is one of the main causes of early gas channeling. In response to this issue, tests were conducted on the variation in the hydrostatic pressure of cement paste over time at different temperatures (30 °C-180 °C), and it was found that the curve of its rapid decrease time point with temperature change conforms to the Boltzmann function. The relationship between the early hydration process and the microstructure of paste at 90 and 150 °C, as well as the changes in hydrostatic pressure, was studied using X-ray powder diffraction, thermogravimetry, and scanning electron microscopy. The results show that the hydrostatic pressure curve of the paste shows a trend of first stabilization and then rapidly decreasing at medium and low temperatures (30 and 90 °C). At high temperatures (150 °C), the pressure curve initially increases until stabilization, enters a stable period, and finally rapidly decreases. In the early stage of hydration induction, there is a large amount of free water between hydration products, and the hydrostatic pressure of the paste remains stable. In the process of hydrostatic pressure reduction, the microstructure of the paste develops from the particle hydration products to a "gel framework", which isolates the pressure transfer of part of the free water. During the acceleration period of hydration, the hydration products enhance the "framework" and reduce the porosity of the paste, completely cutting off the transmission of water pressure, resulting in a rapid decrease in the hydrostatic pressure of the paste. A method for predicting the rapid decrease in hydrostatic pressure of the paste was proposed using the hydration reaction process.

Evaluation of rheo-viscoelasticity of magnesium-silicate-hydrate mixes incorporating different superplasticizers

This study investigated rheo-viscoelastic behaviors of MgO-SiO2 pastes with three phosphate additives (sodium hexametaphosphate (SHMP), sodium trimetaphosphate (STMP), and sodium orthophosphate (SOP)) as superplasticizers. Static yield stress, dynamic yield stress, median differential viscosity, thixotropic loop area, structural recovery rate, and non-destructive structural build-up were analyzed. Furthermore, assessment of hydration and particle dispersion stability was facilitated by employing isothermal calorimetry, XRD, DTG, and zeta potential techniques. SHMP significantly decreased the static and dynamic rheology, thixotropy, and viscoelastic evolution. Samples incorporating 2 wt% SOP exhibited enhanced rheological parameters, particularly static yield stress, owing to increased brucite formation and a denser microstructure in the fresh paste. Adsorption of phosphate additives on MgO surfaces inhibited formation of brucite and improved interparticle electrostatic repulsion, thereby increasing suspension stability. High-efficiency adsorption of SHMP on MgO surfaces, coupled with the retardation of brucite nucleation-and-growth, and enhancement in suspension stability, greatly restrained the rheo-viscoelastic evolution of MgO-SiO2 system.

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.

Influence of water-to-binder ratios on the performance of limestone calcined clay cement-based paste for mining applications

This study aims to investigate the impact of various water-to-binder (w/b) ratios by mass (0.3–2.0) on the performance of limestone calcined clay cement (LC3) pastes. The flowability, setting time, density, unconfined compressive strength, hydration, and microstructure of LC3 pastes under different w/b ratios were thoroughly investigated. The results show that increasing the w/b ratio extends the flowability and setting time while significantly reducing the unconfined compressive strength of LC3 pastes. LC3 pastes with w/b ratios above 0.6 exhibited a final flow diameter surpassing 167 mm, indicating good flowability. The 28-d unconfined compressive strength decreased from 82.3 to 1.3 MPa as the w/b ratio increased from 0.3 to 2.0. This study confirmed that the relationship between unconfined compressive strength and the w/b ratio of LC3 follows Abram’s law. Furthermore, a modified gel/space ratio was proposed to reflect the concentration of solid products, effectively explaining the influence of the w/b ratio on strength, with an R2 of 0.96.

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.

Study on the microstructure and impermeability of calcium aluminate cement containing metakaolin for development of high-performance marine engineering materials

To provide a high-performance marine engineering material, the microstructure and impermeability of calcium aluminate cement (CAC) containing metakaolin (MK) were studied. The chloride penetration resistance of the CAC-MK and Portland cement (PC) mortars was assessed based on physical and chemical barrier effects. The results show that the alumina in MK is more easily dissolved than silica, which inhibits the transformation of CAH10 and prevents microstructural deterioration. Adding 7.5% and 15.0% MK reduces the volume of large pores in the 3-day-old CAC paste by 49.8% and 69.1% while increasing the volume of pores smaller than 50 nm by 175.6% and 242.5%, respectively. Moreover, the microstructure of MK-containing CAC pastes becomes denser with age when cured at 40 °C, enhancing the mechanical strength and water penetration resistance. The CAC mortar containing MK exhibits better resistance to chloride attack than PC mortar, due to the stronger chloride binding capacity and migration resistance.

Enhancement of mechanical and microstructural characteristics of magnesium oxychloride cement with metasteatite

Magnesium oxychloride cement (MOC) has recently garnered considerable research attention as an environmentally sustainable building material. Nevertheless, the mechanical characteristics of MOC have effectively hindered its extensive implementation in engineering structures owing to their inefficient water resistance. In this regard, this study investigates the novel application of steatite to MOC to augment the water resistance of paste. First, steatite was thermally processed to improve the reactivity of the particle and was introduced as a metasteatite with rich magnesium silicate. Furthermore, metasteatite is substituted for MgO in the MOC paste by varying the replacement level from 0 % to 25 % with an interval of 5 %. Thus, metasteatite's effect on MOC paste water resistance is investigated in terms of compressive strength, strength retention under water exposure, and microstructural characterization. Compressive strength results revealed that the influence of metasteatite deteriorated the strength of the matrix with an increased dosage of metasteatite. Moreover, the compressive strength of MOC paste susceptible to water enhanced the strength retention coefficient to 42.9 % for MS10 compared to control specimens. FE-SEM analysis exhibits the formation of M-S-H gel that leads to dense microstructure and contributes to water resistance. In addition, the porosity of the paste is decreased owing to the reaction of Phase 5 with SiO2. The EDS analysis and mapping showed the occurrence of hydration products and the binding affinity between Mg and Si, which improved the continuity of microstructure and water resistance of MOC paste. Therefore, the optimum enhancement is observed for the MOC paste with 10 % metasteatite, demonstrating its efficacy in bolstering water resistance. Finally, this investigation elucidates the feasibility of using metasteatite as a supplementary material for MgO in MOC for developing water resistant MOC.

Underwater carbonation of alkali-activated slag pastes

Carbonation of alkali-activated slag (AAS) materials has been primarily concerned in atmospheres with gaseous CO2. This study, by contrast, highlights that AAS pastes would also be carbonated under tap water immersion. Calcite is the main CO2-bear phase in both sodium hydroxide- and sodium silicate-activated AAS pastes, and the paste pre-cured for a longer curing period shows more severe carbonation. Additionally, calcium carbonate can densify the deteriorated microstructure of sodium hydroxide-activated paste caused by long-term leaching. The indentation modulus of pastes subjected to tap water immersion is higher than those under deionized water immersion. The uptake of CO32- by hydrotalcite (Ht) and gels is also detected, resulting in the formation of Ht-CO3 and decalcification of gels. Due to the synergistic effect of leaching and carbonation, a characteristic layered distribution of pastes close to the exposure front is observed, comprising the carbonated layer, transitional (carbonated + leached) layer, and leached layer, progressing from the outermost to the inner regions. Eventually, the kinetics of underwater carbonation, as well as the discrepancy between dry and underwater carbonation, is revealed.