Stages Of Hydration Research Articles

An investigation into the microstructural evolution and shrinkage control in internally cured mortars with milkweed fibres

This study presented a significant advancement in the use of Milkweed (MW) fibres as internal curing agents in low water-to-cement (w/c) cementitious materials. The research focused on how different pre-treated MW fibres, with different composition, can impact internal curing efficacy in reducing autogenous shrinkage of cement mortars. In addition, the hydration behaviour and microstructural development were revealed using a series of tests including setting time, compressive strength, flexural strength, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA/DTG). A key finding of this study is the remarkable reduction in autogenous shrinkage, with using 0.1 % wt. pre-treated MW fibres leading to up to 28 % reduction at 7 days, compared to plain mortars. Furthermore, internal curing effect resulted in narrowing the compressive strength gap between the reference mixes and those with pre-treated MW fibres in the later stages of hydration. It was also found that the removal of hemicellulose through hybrid treatment can reduce the delay in the final setting time of cement from 45 minutes to 18 minutes. Additionally, while the incorporation of N- and HT-treated MW fibres had negligible effects on drying shrinkage, the inclusion of HY-treated MW fibres led to a 15 % increase in drying shrinkage at 7 days. This difference in behaviour was attributed to the presence of lignin in N- and HT-treated fibres. Lignin was found to play a crucial role in influencing the drying shrinkage, microstructural development, and mechanical properties of MW fibre-incorporated cementitious mixes. Acting as a protective barrier, lignin shielded the MW fibres from cement infiltration into their lumina. Moreover, it served as both a physical and chemical barrier, reducing moisture transport through the capillary network during drying. In conclusion, this study demonstrated the potential of using pre-treated MW fibres as internal curing agents to effectively reduce autogenous shrinkage, with minimal compromise in terms of the compressive strength of cementitious composites.

New impulse-based test method for early-age elastic modulus measurement in cementitious materials

Accurate monitoring of the elastic modulus evolution during the early-age fluid-solid transition in cementitious materials is crucial for understanding their mechanical behavior under early stresses. While existing methods, such as EMM-ARM, have proven effective, they are often associated with high costs or complex setups. This study presents the development of a low-cost, easy-to-implement system that employs impulse excitation applied to a composite beam, introducing the EMM-IRM method for the effective assessment of the elastic modulus of cement paste from the earliest stages of hydration. The use of impulse excitation is particularly advantageous in low-cost systems with accelerometers of lower sensitivity, as it enhances signal clarity and reduces interference from background noise, thereby improving measurement reliability. The system was validated through experimental comparisons with conventional EMM-ARM, cyclic compression, and traditional impulse excitation techniques, using Portland cement paste as the test material. The results show that EMM-IRM consistently estimates the elastic modulus, with a maximum deviation of 6.33% from other methods. Moreover, despite its cost-effectiveness, EMM-IRM demonstrates a higher signal-to-noise ratio compared to conventional EMM-ARM. This approach offers a practical solution for early-age characterization of cementitious materials, balancing cost, simplicity, and measurement accuracy.

Optimizing the content of Li2CO3, Na2SO4 and TEA in fly ash–cement system by response surface methodology

With an optimized dosage, hardening accelerators become a vital means of modifying fly ash-cement system (FAC). This study comprehensively investigated the mechanical properties of FAC modified by Li2CO3, Na2SO4, and triethanolamine (TEA) under different dosages, and optimized the dosage of accelerators through the response surface method (RSM). The synergistic effect of accelerators on the hydration of FAC was characterized by thermogravimetric differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results demonstrated that the factors and response value followed a quadratic polynomial model. The regression coefficients R2 of the model were all greater than 0.9, indicating good agreement with the experimental data. The content of Li2CO3 and Na2SO4 had an extremely significant effect on the compressive strength of 1d and 3d, followed by TEA. The optimal mix ratio predicted by RSM was 0.12% Li2CO3, 0.47% Na2SO4, and 0.40% TEA. Early hydration stages revealed that the combined action of these accelerators increased the formation of CH, CaCO3, and amorphous C-(A)-S-H gel. Microscopically, the surface of fly ash exhibited alkali-induced corrosion, thereby enhancing its pozzolanic reactivity.

Impact of TiO2 powder type on hydration and photocatalytic NOx degradation in cement paste

This study was aimed at developing novel functional construction materials with NOx removal capabilities using TiO2 powder. To this end, the effects of the chemical composition of TiO2 powder on the hydration process and the mechanical properties of cement were investigated. The hydration characteristics of the cement were assessed by analyzing the setting time and heat of hydration, while the mechanical properties were evaluated by measuring compressive strength at different curing ages. Additionally, the NOx degradation performance was examined. The results demonstrate that TiO2 powder accelerates the hydration of cement, enhancing the compressive strength during the early stages of hydration. Furthermore, the NOx degradation performance of mortar specimens was enhanced with the incorporation of TiO2 powder. However, the extent of these improvements varied significantly depending on the chemical composition of the TiO2 powder, with the composition ratio of anatase and rutile being particularly influential. When utilizing TiO2 powder to enhance the performance of construction materials or impart new functional properties, it is advisable to consider the composition of the TiO2 powder to ensure alignment with the intended performance improvement objectives.

Substitution of blast furnace slag by melting furnace slag as active component in green concrete application

Blast furnace slag (BFS), a commonly used substitute for cement clinker, is in large demand and gradually increasing in price. Melting furnace slag (MFS), a by-product of the co-disposal of waste incineration fly ash and metallurgical dust sludge, has potential hydration properties, and its large accumulation also poses a serious threat to the environment. In this study, we focus on the effect of MFS replacing BFS on concrete properties and its hydration mechanism. Results showed that MFS significantly enhanced the compressive strength at the later stage of hydration, and the 28-d compressive strength of MSD concrete was 15.15 % higher than BSD concrete. MFS enriched with a large amount of amorphous silica and alumina played a key role in the hydration process. This is mainly shown as the increase in the fluctuation of Si-O and Al-O bond strengths and the decrease in the energy separation between Ca 2p and Si 2p levels. In addition, the increased substitution of aluminum for silicon in MSD results in the formation of C-A-S-H gels, which are tightly bonded with ettringite to form a composite structure. Subsequent durability assessments indicate that the incorporation of MFS diminishes the permeability to chlorides and sulfates, while also bolstering the concrete’s resistance to carbonation. These findings imply a positive impact on the concrete’s enduring service life.

The Impact of Fly Ash on the Properties of Cementitious Materials Based on Slag-Steel Slag-Gypsum Solid Waste.

This paper presents a novel low-carbon binder formulated from fly ash (FA), ground granulated blast furnace slag, steel slag, and desulfurization gypsum as a quaternary solid waste-based material. It specifically examines the influence of FA content on the mechanical properties and hydration reactions of the quaternary solid waste-based binder. The mortar test results indicate that the optimal FA content is 10%, which yields a 28-day compressive strength 11.28% higher than that of the control group without FA. The spherical particles of fly ash reduce the overall water demand and provide a "lubricating" effect to the paste due to their continuous gradation, improving the fluidity of the slag-steel slag-gypsum cementitious materials. The micro test results indicate that fly ash has minimal effect on the early hydration products and process of the solid waste-based cementitious materials, but after 7 days, it continuously dissolves silicon-oxygen tetrahedrons or aluminum-oxygen tetrahedrons, consuming Ca2+ and OH- in the system. After 28 days, the amount of ettringite and C-(A)-S-H gel generated increases significantly. The pozzolanic activity of fly ash is mainly stimulated by the Ca(OH)2 from steel slag in the later hydration stage. Additionally, spherical fly ash particles can fill the voids in the hardened paste, reducing the formation of cracks and weak zones, and thereby contributing to a denser overall structure of the hydrated binder. The findings of this paper provide data support for the development of low-carbon cement-free binders using fly ash in conjunction with metallurgical slags, thereby contributing to the low-carbon advancement of the construction materials industry.

Effect of fly ash and nano Silica on the formation and evolution of Calcium Silicate Hydrate in Portland Cement during hydration process

Recently, the trend of replacing cement with mineral admixtures in concrete has witnessed increasing interest in the construction industry due to the reduction in embodied energy and CO2 emissions. However, the addition of these admixtures in Portland Cement (PC) affected the formation as well as the structure of the hydration product Calcium-Silicate-Hydrate (C-S-H), which is reflected in the mechanical and durability properties of cement concrete. In the present study, nano-silica (NS) and a mixture of fly ash (FA) and NS were replaced into PC (PC + 0.5 % NS, PC + 1 % NS, PC + 0.5 % NS + 20 % FA and PC + 1 % NS + 40 % FA) to systematically study the formation and structural evolution of hydration products, namely C-S-H, at atomic and micro-scales at the early stage of hydration (3 days) and a later stage of hydration (90 days). The formation and structure of C-S-H were analyzed to correlate the microstructure development by using XRD, Rietveld technique, FESEM, TEM, FTIR and nano-scale mechanical properties by employing the nanoindentation techniques. Atomic Pair Distribution Function (PDF) is used to understand the effect of admixtures on the C-S-H structure from atomic point of view. PDF shows the structural modification of C-S-H such as different polyhedral, separation of intralayer/interlayer, pair/bond length, coordination number of atoms corresponding to the addition of additives with hydration age. Also, porosity measurements show increasing or decreasing porosity during hydration with additives. It is observed that the contribution of low-density C-S-H (LD C-S-H) is greater than that of high-density C-S-H (HD C-S-H) in the beginning days, whereas HD C-S-H more than LD C-S-H in the latter days of hydration. The elastic modulus increased from 15.44 GPa to 19.82 GPa and the hardness decreased from 0.41 GPa to 0.35 GPa of LD C-S-H in early days, whereas elastic modulus decreased from 34.84 GPa to 29.33 GPa and the hardness increased from 0.75 GPa to 0.83 GPa of HD C-S-H in the latter stage due to addition of additives. However, both increased for LD C-S-H and HD C-S-H for each corresponding mixture during hydration. The present study reported the formation and microstructural modifications of C-S-H and the correlation with nano-mechanical properties due to addition of nano or micro-sized admixtures (nano silica and fly ash) in the cement system. This correlation helps to develop low-energy cement composites by tailoring cement systems with desired properties.

Experimental study on the macroscopic and microscopic properties of cement paste backfill after treatment with carbon dioxide carbonize filling slurries during the mixing process

Introducing CO2 during the mixing process of filling slurry for wet carbonation enables simultaneous carbonation and hydration reactions of the carbonated filling slurry (CSL). This study evaluates the microstructural evolution and strength development of carbonated cemented paste backfill (CCPB) under different carbonation times, and discusses the carbonation products and carbon sequestration of CCPB. The results reveal that introducing 99% pure CO2 at a flow rate of 1 L/min for 10 min into the filling slurry in a non-sealed container effectively optimizes the microscopic pore structure and mechanical properties of CCPB, achieving a carbon sequestration rate of 6.42%. Short-term carbonation leads to a continuous decrease in the T2 relaxation signal of CSL in the early hydration stage, enhancing pore structure by converting secondary pores to micropores. The main carbonation product is calcite crystalline CaCO3, which forms a dense carbonation layer on the surface of the tailings particles. However, prolonged carbonation results in the formation of microscopic pore encapsulation layer, hindering further CO2 diffusion, reducing carbonation efficiency, and deteriorating the mechanical properties of CCPB. With a carbonation time of 10 min, the UCS and EM of CCPB with different cement-to-tailings ratios show significant improvement, and the specimens exhibit lower fragmentation and fewer secondary cracks, maintaining better integrity after failure. In conclusion, the wet carbonation of filling slurry not only enhances the strength of the filling material but also achieves the reutilization of gaseous and solid wastes through carbon sequestration filling method, providing an efficient and eco-friendly solution for mine backfilling.

Study on the hydration characteristics, mechanical properties, and microstructure of thermally activated low-carbon recycled cement

Based on the thermal activation method, utilizing fine particles of waste concrete to prepare low-carbon recycled cement (RC) is currently one of the research hotspots. Based on existing literature research results, this paper identifies four calcination temperature conditions (120, 450, 750, 1000 ℃) and uses replacement rates of 10 %, 30 %, 50 %, 70 %, and 100 % of RC to replace ordinary Portland cement (OPC).The main physical properties, hydration characteristics, mechanical properties, and microstructure of RC are studied. The study elucidated the influence of RC thermal activation temperature, replacement rate, fineness, and age on its hydration characteristics, mechanical properties, and microstructure, establishing a macro-micro correlation for RC and revealing the mechanism of improvement in mechanical properties of thermal-activated RC. The research indicates that in the initial stage of hydration, RC exhibits a relatively fast hydration rate, with higher initial total heat release than OPC. Hydration products include internal hydration products (formation of C-(A)-S-H gel) and external hydration products (formation of plate-shaped AFm). Furthermore, RC exhibits a faster hydration rate at a hot activation temperature of 750°C, with CH and C-S-H gel transforming into the highly hydrated α´L-C2S, forming a denser microstructure at an early stage. Moreover, at a replacement rate of 30 %, the compressive strength of cement mortar reaches its optimum at 28 days, achieving 13.81 MPa, equivalent to 60.7 % of OPC cement mortar, with a 66.67 % reduction in carbon emissions. Microstructure analysis reveals that when the temperature reaches 1000°C, excessive combustion of RC leads to the formation of low-reactivity C2AS and β-C2S, resulting in a decrease in macroscopic mechanical properties. Additionally, increasing the fineness of RC significantly enhances its rehydration capability, especially as the age increases. This study is of great significance for the preparation of green cement-based composite cementitious materials.

Effect and mechanism of phase change lightweight aggregate on temperature control and crack resistance in high-strength mass concrete

Under temperature stress, high-strength mass concrete is brittle due to its high total heat of hydration. In this study, a control mixture of C55 high-strength mass concrete meeting the performance requirements was prepared. The effects of different functional aggregates on the thermal properties, such as setting and hardening rate, peak temperature, and temperature rise and fall rate in the early stage of cement hydration, as well as the effects of functional lightweight aggregates on the workability, mechanical properties, and deformation properties of concrete, were investigated in this paper using two types of aggregates with thermal insulation and phase change energy storage functions. The study shows that, in addition to having some early strength impacts and temperature management capabilities, thermal storage coarse lightweight aggregate (PCCLA) and thermal insulation fine lightweight aggregate (TIFLA) can both increase the workability and crack resistance of concrete. When it comes to temperature regulation, thermal storage coarse aggregate outperforms thermal insulation functional aggregate significantly. Thermal insulation fine aggregate can improve the rate of setting and hardening, while coarse thermal storage aggregate may work as in-situ self-heating curing in the early stages due to its phase change energy storage. This quickens the rate of setting and hardening and increases the resistivity of the set period, which in turn increases the rate of drying shrinkage.

Hydration and microstructure formation of magnesium oxysulfate (MOS) cement regulated by sepiolite with high adsorption ability

Magnesium oxysulfate (MOS) cement is a potential low-carbon cementitious material with its characteristic depending on the reaction between light-burned magnesia (LBM) and MgSO4 solution. This work aimed to elucidate the effect of sepiolite with high adsorption ability on regulating the reaction within MOS cement. Replacement levels of LBM by sepiolite at 2 and 5 wt% were adopted. Hydration kinetics, microstructure, phase composition and compressive strength of MOS cement without and with sepiolite were studied. Results showed that adding sepiolite into MOS cement adjusted the ion distribution at the early hydration stage and promoted the reaction with an early onset of heat flow peaks. The presence of sepiolite refined the morphology of formed needle-like 5 Mg(OH)2·MgSO4·7H2O (517 phase) and strengthened the bond water within its structure. The high adsorption ability of sepiolite enabled the nucleation of 517 phase and amorphous phase onto its surface. Sepiolite also densified the poorly hydrated regions by tightly combining with the incompletely hydrated MgO grains. Consequently, compressive strength of MOS cement under air curing was improved after adding sepiolite.

Effect of nano-metakaolin on the early-age fracture properties of cement mortar

In this paper, the fracture performance of nano-metakaolin (NMK) cement mortar during early hydration period was investigated. Different NMK contents (0 %, 3 %, 5 %, 7 %) were considered, and three-point bending tests were conducted. The digital image correlation technology and acoustic emission technology were utilized to analyze P-CMOD curves, initial fracture toughness, unstable fracture toughness, fracture energy, cumulative AE hits, and cumulative AE energy, AE source locations of cement mortar at early hydration stages. Furthermore, SEM experiments were utilized to analyze the mechanism by which NMK affects fracture performance of cement mortar. The results indicate that the incorporation of NMK enhances the fracture properties of cement mortar, with the most suitable NMK content being 5 %. The addition of NMK increases the cracking load, peak load, and the CMOD at the peak load of the cement mortar at 3 d, 7 d, and 14 d. The cracking load and fracture energy of the cement mortar with 5 % NMK increase by 22.5 % and 35.7 % respectively, compared to ordinary cement mortar at 14 d. NMK enhances the initial fracture toughness and unstable fracture toughness of the cement mortar, improving its crack propagation resistance. The unstable fracture toughness of the cement mortar is the largest when the NMK content is 5 % at 14 d, which is 31.6 % higher than that of ordinary cement mortar. Furthermore, NMK increases the cumulative AE energy and fracture energy of the cement mortar, increasing the cumulative ring counts and cumulative AE hits, causing the crack propagation path to deviate and resulting in improved crack resistance. The cumulative ring counts and AE hits for the cement mortar with 5 % NMK are 42.9 % and 66.2 % higher, respectively, than those for ordinary cement mortar at 14 d. NMK significantly modifies the cement matrix, thereby enhancing the fracture resistance of cement mortar.

Mechanical properties of sisal fiber-reinforced fly ash cement mortar activated by sodium sulfate

The substantial use of fly ash as cement replacement to reduce carbon emissions is identified as the primary goal, 50 % of the cement was substituted with fly ash and in order to avoid the low early stage mechanical properties of the composite, varying doses of sodium sulfate were used as an activator of fly ash. Additionally, sisal fibers were chosen to enhance the flexural strength. The results indicate that sodium sulfate significantly enhances the early stage mechanical performance of the cementitious composites and the matrix exhibits the optimal mechanical performance at 4 wt% sodium sulfate dosage (4SS). The addition of sisal fibers resulted in an enhancement of the flexural performance of the material. The collaboration between sodium sulfate and sisal fibers results in an improvement in the initial flexural performance of the material while preserving its compressive strength. The single-fiber pullout test further confirmed that adding sodium sulfate enhances the fiber-matrix interface and bonding. Microstructural investigations by XRD, TGA, MIP, and SEM-EDS revealed accelerated hydration and early formation of a large amount of ettringite due to the addition of sodium sulfate. Ettringite acts as a gel nucleation seed, promoting the formation of a dense gel structure and effectively improving the early mechanical properties of the composite. Furthermore, with curing age, sodium sulfate also effectively improves the pore structure of the matrix in the late hydration stage.

Cell Wall Profiling of the Resurrection Plants Craterostigma plantagineum and Lindernia brevidens and Their Desiccation-Sensitive Relative, Lindernia subracemosa.

Vegetative desiccation tolerance has evolved within the genera Craterostigma and Lindernia. A centre of endemism and diversification for these plants appears to occur in ancient tropical montane rainforests of east Africa in Kenya and Tanzania. Lindernia subracemosa, a desiccation-sensitive relative of Craterostigma plantagineum, occurs in these rainforests and experiences adequate rainfall and thus does not require desiccation tolerance. However, sharing this inselberg habitat, another species, Lindernia brevidens, does retain vegetative desiccation tolerance and is also related to the resurrection plant C. plantagineum found in South Africa. Leaf material was collected from all three species at different stages of hydration: fully hydrated (ca. 90% relative water content), half-dry (ca. 45% relative water content) and fully desiccated (ca. 5% relative water content). Cell wall monosaccharide datasets were collected from all three species. Comprehensive microarray polymer profiling (CoMPP) was performed using ca. 27 plant cell-wall-specific antibodies and carbohydrate-binding module probes. Some differences in pectin, xyloglucan and extension epitopes were observed between the selected species. Overall, cell wall compositions were similar, suggesting that wall modifications in response to vegetative desiccation involve subtle cell wall remodelling that is not reflected by the compositional analysis and that the plants and their walls are constitutively protected against desiccation.

Effect of Composite Fibers and Fly Ash on the Properties of Portland–Sulfoaluminate Composite Cement-Based Grouting Sealing Materials

Current conventional cement materials are no longer able to meet the actual usage needs of geotechnical engineering. In order to improve the workability of cement materials used in geotechnical, transportation, and mining engineering, it is necessary to improve the formulation of cement materials. Polypropylene fibers (PVAF), polyvinyl alcohol fibers (PPF), and fly ash (FA) are used in this study to modify Portland–sulfoaluminate composite cement to improve the workability of the cement material system. Meanwhile, the microstructure that affects the system performance was also studied. The research results indicate that adding FA to the composite cement system can improve its fluidity. In the later stage of hydration, due to the volcanic ash reaction, the production of hydration products will increase, but it will not affect the type of hydration products. Adding PPF-PVAF can effectively improve the strength performance of the cement system. The compressive strength reached 24.61 MPa after 28 days of curing, which was 13.8% higher than the blank sample. Adding calcium hydroxide powder and FA to the system can improve the fluidity of the cement system to a certain extent and positively impact the later strength. After 28 days of curing, the compressive strength of experimental group 9 reached 30.21 MPa, which increased by 70.5% compared to after 7 days These results were found at the microscopic level, based on analyses via XRD, TG, and SEM. The Mix-EXP cured for 28 days has better hydration product content and composition arrangement of cement slurry than the O-S-C cured for 28 days.

High temperature calcined red mud-cement mortar: Workability, mechanical properties, hydration mechanism, and microstructure

To efficiently utilize red mud (RM) in cement-based materials, this study employed high-temperature calcination to enhance RM's pozzolanic activity. Calcined RM replaced cement in RM-cement mortar, examining the effects of different calcination temperatures and RM addition amounts on the workability and mechanical properties of the mortar. Additionally, XRD, FTIR, SEM-EDS, TAM-Air, and TG were used to explore the hydration mechanism and microstructure of RM-cement mortar. Research showed that as the calcination temperature increased, minerals like Calcite, Hematite, and Cancrinite in RM began to decompose, and the glassy structure increased. At 800 °C, the serrated and amorphous diffraction peaks significantly increased. Calcined RM positively influenced the setting and hardening of cement mortar but negatively affected its fluidity. The optimal calcination temperature for RM was 800 °C, with an optimal addition amount of 10%. The compressive strengths of RM-cement mortar at 3, 7, and 28d, with optimal conditions, are 9.62, 29.94, and 40.12 MPa, respectively, showing increases of 4.25, 1.72, and 1.39 times over untreated RM-cement mortar. When RM was calcined to 800 °C, the diffraction peak intensities of Portlandite, C–S–H, and Ettringite in the RM-cement paste were the highest, and the hydration products interwove to form a dense microstructure. Adding calcined RM extended the induction period of cement, increased the rate of heat release, shortened the acceleration period, and further accelerated the rate of heat release. Nevertheless, the alkaline components in calcined RM pose a certain hindrance to the later stages of cement hydration. In summary, calcining RM to 800 °C enhanced its pozzolanic activity, improved the workability, early hydration, and early strength of cement, and reduced cement consumption and CO2 emissions.

Ultrasonic wave diffusion-based investigations on microstructural development in multi-scale cementitious materials

Microstructural study of cement and its composites has immense significance from both fundamental and applied research points of view. Concrete, a mesoscale cementitious material, possesses high heterogeneity and inherent complex behavior. The multi-phases of concrete show an evolving nature at any instance of time, starting from the initiation of hydration to the complete maturity level. The hydration products and the aggregate-matrix Interfacial Transition Zone (ITZ) play a crucial role in defining the microstructural arrangement, which determines the mechanical and durability properties. Ultrasonic diffusion-based study has a unique advantage for characterising microstructural behavior in heterogeneous materials as it can decouple the different attenuating parameters- diffusivity (D) and dissipation (σ), where, D reflects the material microstructure and σ indicates the viscoelastic property of the base material. For that purpose, an ultrasonic diffusion study has been carried out in the present research for hydration monitoring in two scales, cement (micro-scale), and concrete (meso-scale) under different transmission modes. Ultrasonic measurements have been processed in the time-frequency domain to deduce the diffusivity and dissipation parameters using Spectral Energy Density distribution over the entire time window. The present research reveals the key findings as follows: (1) the influence of microstructure in ultrasonic wave propagation can be explicitly demonstrated using diffusion based analytical formulation and experimental results; (2) ultrasonic parameters (in terms of diffusivity and dissipation) can provide physical information on microstructural development in cementitious material during its hydration stage; and (3) the diffusion based method can distinguish the complex microstructural behavior across the scales of heterogeneity- micro-scale (cement paste) to meso-scale (concrete).

Hydration of mafic crustal rocks at high temperature during brittle‐viscous deformation along a strike‐slip plate boundary

AbstractThe Poroshiri ophiolite (Hidaka metamorphic belt, Japan) occurs within a crustal‐scale network of high‐temperature, dextral shear zones that accommodated hundreds of kilometres of displacement due to the opening of the Japan Sea in the Neogene. The opholitic rocks comprise ultramafic, mafic and sedimentary protoliths that have been variably hydrated and metamorphosed. This work investigates the mechanisms and timing of fluid influx relative to viscous deformation in metagabbros and amphibolites deformed during exhumation from granulite‐ to amphibolite‐facies conditions. We consider a range of microstructures, from low strain domains and 1–2 mm thick shear bands to mylonites with a thickness of a few meters. Low strain domains of metagabbros exhibit corona textures with symplectites consisting of pargasitic amphibole (Ed0.7) ‐ anorthitic plagioclase (An80–92) ± orthopyroxene ± clinopyroxene forming around olivine and igneous pyroxene and with similar plagioclase–amphibole‐orthopyroxene ± clinopyroxene granoblastic aggregates in micrometric‐thick fractures. These textures result from hydration under low fluid‐rock ratio, with elevated H2O content only occurring locally (H2O > 1–1.2 wt%). Igneous mineral replacement leads to grain size reduction from 1 mm to ~10 μm. Amphibole exhibits a strong core‐rim zonation primarily controlled by the high diffusivity of Fe, Mg and OH and the low diffusivity of Al. Mineral compositional equilibrium is achieved at the scale of 100–200 μm. In mm‐thick localized shear bands and in metric‐scale mylonitic amphibolites, the heterogeneous mineral composition of amphibole (Ed0.2–0.5) and plagioclase (An40−An80) indicates only partial re‐equilibration (at the scale of 200–500 μm) despite higher fluid‐rock ratios and more pervasive fluid percolation than in metagabbros. Plagioclase–amphibole thermometry and equilibrium phase diagrams indicate that the initial fluid infiltration and corona formation occurred at 800–850°C by fracturing and percolation along grain boundaries. This was followed by the main fluid percolation and mylonitization event, which occurred during exhumation and cooling at conditions of 720–580°C, ~4 kbar. Continuous hydration during retrogression was achieved by the influx of dominantly seawater‐derived fluid, as attested by the high chlorine (Cl) contents (>300–400 ppm) of amphiboles in fractures. The heterogeneous distribution of fractures controls the distribution of fluid from the earliest stages of hydration, creating positive feedback where the growth of hydrous minerals as amphibole (up to +300 vol% of amphibole in high strain areas relative to the low‐strain ones) and the formation of fine‐grained mixed domains that led to further localization of viscous strain and mass transfer (variations of ± 30–40% in major elements). The Poroshiri ophiolite therefore represents a good fossil example of a former transpressional plate boundary where coupled metamorphic and deformation processes were triggered by seawater‐derived fluid that percolated to depths of ~15 km.

Ultrasonic wave characteristics in multiscale cementitious materials at different stages of hydration

Monitoring the microstructural change in cementitious materials during hydration is an essential but challenging task. Therefore, a non-invasive and sophisticated technique is warranted to understand the microscopic behaviour of the multiphase cementitious materials (where the length scale of the constituents varies from centimeters to micrometers) in different stages of hydration. Due to exothermic hydration reactions, different hydration products start to evolve with individual mechanical properties. In concrete, an interface transition zone (ITZ) appears between the aggregate surface and paste matrix, which influences the overall properties of concrete material. In the present research, 1) several wave characteristics, such as wave velocity, energy distribution, and signal phase are found out using Ultrasonic Pulse Velocity (UPV), Wavelet Packet Energy (WPE) and Hilbert Transform (HT) methods, to monitor the hydration mechanism (1d-28d) in cement-based materials with two levels of heterogeneities (cement paste and concrete, representing microscale and mesoscale, respectively). Also, the unique nonlinear behaviour is studied in the frequency domain using the promising Sideband Energy Ratio (SER) and Sideband Peak Count Index (SPC-I) methods. 2) Numerical simulations are carried out to understand the wave interaction in the developing microstructure. A discretized microstructure of cement shows microscopic details of each phase at any instant of hydration (e.g., formation stage and after complete maturity level). The experimental and numerical investigations on the characteristics of the nonlinear ultrasonic wave propagation show the impact of microstructural development of multi-scale cementitious materials during hydration.

Hydration characteristics and kinetic analysis of polyacrylamide (PAM) anti-dispersion cement-based materials

Abstract Through phase analysis and quantitative calculations of the hydration process, the inclusion of polyacrylamide (PAM) in Anti-dispersion Water Paste affects its hydration characteristics is discovered. Specifically, the presence of PAM reduces early reactivity while accelerating progress in the middle to late stages of hydration. By employing K-D hydration kinetic analysis, it is confirmed that the use of PAM results in the formation of a multi-nucleation homogeneous point system within the cement slurry. This system prolongs the NG (nucleation and growth) process time, increases the hydration degree during the transition from NG to I (induction) process, and inhibits the heterogeneous precipitation of hydration products. Consequently, the early hydration of cement is hindered. As the hydration reaction advances, the microstructure of the product under multi-nucleation points increases the specific surface area. This gradual breakthrough of the hydration threshold barrier shortens the duration of the phase boundary reaction process and reduces the hydration degree during the I and D (diffusion) processes. Consequently, the late-stage hydration rate is accelerated.