Early Hydration Research Articles

Rice husk ash and recycled sand as synergistic substitutes in ultra-high performance concrete: Microstructural, mechanical performance, and eco-economic analysis

Quartz sand and silica fume (SF), commonly used in UHPC production, are costly and contribute to dust pollution and significant carbon emissions. In this work, we explored the preparation of an environmentally friendly ultra-high performance concrete (e-UHPC) by substituting SF and quartz sand with rice husk ash (RHA) in ratios of 10 %, 20 %, and 30 %, and recycled building sand (RS) in ratios of 25 %, 50 %, and 75 %. We assessed the impact of these substitutions on workability, mechanical strength, hydration products, and the micromechanical characteristics of the interfacial transition zone. In addition, an environmental and economic assessment index for e-UHPC was introduced. Results showed that while RHA and RS reduced the flowability of e-UHPC, RHA helped mitigate the compressive strength loss due to RS (3.9 %-9.7 %). RHA accelerated early hydration, and improved densification in the transition zone, enhancing late hydration and refining the pore structure of e-UHPC. Notably, a 10 % RHA replacement rate optimally improved early hydration efficiency and minimized CH content. The combination of 10 % RHA and 25 % RS proved most effective in optimizing the interfacial transition zone and improving the pore structure of e-UHPC. Importantly, e-UHPC reduces the carbon footprint at a lower cost and offers significant environmental and economic advantages over traditional UHPC. The results of this study will promote the incorporation of construction and agricultural wastes into concrete.

Impact of treated sewage water on early strength development of calcium sulfoaluminate cement paste: A comparative study

This study investigates the use of treated sewage water (TSW) as a substitute for fresh tap water (FTW) in concrete production using calcium sulfoaluminate (CSA) cement. The research addresses concerns about freshwater scarcity and emphasizes CSA cement's rapid setting properties, crucial for emergency constructions like military airfield recovery. The focus is on the early-age properties of CSA paste mixed with TSW, with assessments conducted at 4 hours, 1 day, and 3 days post-mixing. Key parameters, including slump, setting times, and hardened characteristics, were evaluated. TSW contained significant metal concentrations and a high pH, with total dissolved solids exceeding FTW by 67%, yet all parameters remained within acceptable limits. Analytical techniques identified ettringite (AFt) as a primary hydration product, while ye'elimite (C4A3Š) was present as a component of the unhydrated clinker in the CSA cement. Simulations showed improved stability in the TSW-CSA interface compared to FTW, although early hydration was slower, likely due to delayed C4A3Š hydration and increased AFt formation. Initially, CSA/TSW pastes presented a refined microstructure, which altered by 3 days. Despite a 14% faster final setting time, compressive strength was 21% lower at 4 hours. These findings highlight TSW's potential as a sustainable alternative in CSA cement mixing, necessitating further research for long-term performance evaluation.

Optimization design of ultra-fine supplementary cementitious materials ultra-high performance concrete mix proportion based on orthogonal experiment

Traditional ultra-high performance concrete has problems such as high viscosity, high early-age autogenous shrinkage, and high heat release during early hydration. In recent years, with the development of ultra-fine grinding technology, ultra-fine supplementary cementitious materials (USCMs) have received widespread attention, which have higher pozzolanic activity than traditional supplementary cementitious materials. This study investigated the effects of water-binder ratio, silica fume content, and ultra-fine supplementary cementitious materials (USCMs) content on the workability, mechanical properties, and early-age autogenous shrinkage of ultra-high performance concrete (UHPC) based on orthogonal experiments. In orthogonal experiments, multiple factors and levels were introduced, and a combination of range analysis, variance analysis, and multi-factor interaction analysis were combined to determine the optimization level range of each factor. The results showed that the water-binder ratio had the greatest impact on the fluidity, compressive strength, and autogenous shrinkage of UHPC; The content of silica fume had the greatest impact on the flexural strength of UHPC. Compared with the control group, USCMs can significantly improve the workability and rheological properties of UHPC, reduce early hydration heat release, and inhibit the autogenous shrinkage of UHPC.

Study on the fluid-solid transition mechanism of natural hydraulic lime pastes: Consider the water to binder ratio and polycarboxylate superplasticizer

Natural hydraulic lime (NHL) is used as a grouting material in the restoration of ancient buildings, the formation and evolution of its early workability are crucial for the reliability of the restoration effects. This paper conducts an in-depth study on the effects of water to binder (w/b) ratio and polycarboxylate superplasticizer (SP) dosage on the viscoelastic properties of fluid-solid transition process in NHL paste through tests on the fluidity, rheological characteristics, micro-rheology, hydration heat release, and early phase composition. The results show that the fluidity of NHL paste significantly increases with increasing w/b ratio and SP dosage, while its yield stress and plastic viscosity show downward trend, and it has shear thinning characteristics. In the initial stage, elevated w/b ratio leads to the significant reduction in both macroscopic viscosity index (MVI) and elastic index (EI) of NHL paste, along with delayed rapid increases, the effect is even more pronounced by adding SP. High w/b ratio or adding SP are able to enhance the dispersed state of solid particle in NHL pastes, the viscoelastic transition point of NHL paste is delayed and the viscoelastic transition time is prolonged. Increasing the w/b ratio and adding SP both inhibit the early dissolution and hydration of NHL paste, affecting the fluid-solid transition process. Overall, as the spatial network gradually develops by the solid particles dissolve and continue to hydrate, NHL paste undergoes a transition from a viscous fluid to an elastic semi-fluid state, exhibiting low strength and noticeable plasticity characteristics. With further hydration, NHL paste initiates consolidation and hardening processes, progressively transforming from a plastic semi-fluid into hardened paste.

Understanding the time-dependent rheological behavior of seawater mixed cement paste with fly ash

Due to the relative scarcity of freshwater resources in coastal regions, the use of seawater in concrete construction has great potential due to its benefits in cost and resource. To further advance the application of seawater concrete, a deeper understanding of its rheological properties is essential. This study investigates the effects of fly ash on the time-dependent rheological behavior of seawater cementitious paste, such as yield stress, plastic viscosity, and structural build-up rate. The underlying mechanisms are analyzed using the theories of water film thickness (WFT), ion concentration, and hydration heat. The research findings confirm that the rheological parameters of seawater paste are generally higher than those of deionized water paste, regardless of the cementitious compositions. As fly ash content increases, the plastic viscosity of seawater paste increase, while the fluidity and dynamic yield stress decreases. Further analysis reveals that the decrease in the yield stress with fly ash content is well related to the increase in the WFT, but it cannot sufficiently explain the change of yield stress over time. Instead, the amount of hydration products in seawater paste shows a linear increasing relationship with the dynamic yield stress at 65 min. By contrast, the plastic viscosity can be related to the ion concentration in the interstitial solution, wherein an increase in the concentration of Ca2+ corresponds to an increase in the plastic viscosity. Moreover, the rheological parameters increase over time, with the growth rates between 5 and 35 minutes being higher than those between 35 and 65 minutes, possibly due to the rapid early hydration of the binder materials. This study offers a fundamental theoretical support for the use of seawater in various concrete applications.

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.

Investigation of early hydration of cement by hydrogen nuclear magnetic resonance (1H NMR): new insights into paramagnetic effect

Investigation of early hydration of cement by hydrogen nuclear magnetic resonance (1H NMR): new insights into paramagnetic effect

Study on the hydration characteristics and mechanical properties of recycled powder-slag powder-cement system

This study systematically investigated the influence of different blending ratios of recycled powder and slag powder on hydration heat evolution and mechanical properties. Various modern microscopic testing techniques were employed to quantitatively characterize hydration products and microstructures, revealing their hydration mechanisms. The results indicate that both recycled powder and slag powder can accelerate the early hydration rate. When recycled powder and slag powder are co-blended, their early hydration rate and cumulative heat release surpass those of specimens with single additions of recycled powder. Moreover, the mechanical properties in the later stage are superior to those of specimens with single additions of recycled powder. At 60d, the PRS70-1-2 in the multi doped recycled powder and slag powder system even exceeds that of the uni doped SL system, but is much higher than that of the uni doped RP system，the compressive strength of the multi doped recycled powder and slag powder system increased by 25.5%, 37.1% and 36.9%, respectively, compared with that of the uni doped RP system. Specimens with single additions of recycled powder and slag powder have a relatively high proportion of harmful and very harmful pores. At 28d, the porosity of the multi doped recycled powder and slag powder system decreased by 19.2%, 24.2% and 14.8%, respectively, compared with that of the uni doped RP system. However, when recycled powder and slag powder are co-blended, the proportion of harmful and very harmful pores decreases, while the proportion of less harmful and harmless pores increases. This leads to an overall reduction in porosity and an improvement in mechanical properties.

Utilizing diatomaceous earth (DE) as a sustainable substitute in alkali-activated cementitious materials: Performance and life cycle assessment

As the demand for alkali-activated cementitious materials (AACM) increases, reliance on blast furnace slag (BFS) raises concerns about potential shortages. This study evaluates the substitution of BFS with diatomaceous earth (DE) in AACM, using three DE types—raw (RDE), calcined (CDE), and spent (SDE)—at substitution rates of 0–30 %. The impact of these substitutions on fluidity, setting time, and compressive/flexural strength of the prepared mortar was assessed, along with an analysis of the mechanisms through hydration heat, product composition, and pore structure. Results indicate that DE, characterized by the porous structure and high content of amorphous silica, enhances early hydration, reduces fluidity, accelerates setting times, and refines pore structure, thereby improving strength. CDE, with its low organic content and large surface area, exhibited the best performance, while SDE was effective despite impurities, and RDE performed the poorest. Increasing DE substitution raised water absorption, impacting fluidity and setting times, with 20 % identified as the optimal substitution rate, balancing strength and workability. The entropy method-analytic hierarchy process (EM-AHP) confirmed this rate, with CDE as the optimal variant. Life cycle assessment (LCA) showed that while SDE reduces environmental impacts significantly, CDE achieves a greater reduction when considering both environmental and mechanical performance. In conclusion, CDE and SDE are viable BFS substitutes in AACM, offering enhanced performance and reduced environmental impacts.

Preparation of C-S-H seeds from waste glass powder and its effect on early performance of cement paste

This study investigates the hydrothermal synthesis of calcium silicate hydrate (C-S-H) seeds using nano-size glass powder (NGP) derived from siliceous raw materials and CaO as the calcareous precursor. The influence of varying NGP concentrations on the particle size, microstructure, and phase composition of the C-S-H seeds was systematically analyzed. The synthesized C-S-H seeds were subsequently employed as additives to evaluate their effects on the early hydration process and compressive strength development of cement paste. The results indicate that increasing the NGP concentration from 0.2 mol/L to 0.8 mol/L leads to an exponential increase in the median particle size of the C-S-H seeds from 147 nm to 1328 nm and a corresponding morphological transformation from flocculent to granular structures. Additionally, the purity of the C-S-H sample decreased from 74.8% to 54.5% as the NGP concentration increased. The addition of C-S-H seeds can increase the 12h compressive strength of cement pastes by 15.5%–53.5%. This improvement is due to the accelerated early hydration kinetics induced by the C-S-H seeds, which act as nucleation sites, thereby increasing the nucleation and growth rates by 31.4% and 53.2%, respectively.

Absorption and Release mechanism of superabsorbent polymers and its impact on shrinkage and durability of internally cured concrete – A review

Superabsorbent polymers (SAP) are considered as a promising assortment of chemical admixtures which present novel prospects for influencing the properties of cementitious materials in the fresh, setting, and hardened states. However, the diversity of commercial SAP, especially in terms of monomers, crosslinking agents, and synthesis methods, still poses many obstacles in their large-scale application. Therefore, this review aims to shed light on intrinsic absorption and release mechanism of various SAP and its impact on rheological properties, mechanical properties, shrinkage properties, and durability for cementitious materials. Our research findings indicate significant differences in the water absorption and release mechanisms between ionic and non-ionic SAP. The swelling of non-ionic SAP is dependent on the osmotic pressure formed between the polymer network and the solution. In contrast, ionic SAP not only exhibits osmotic properties but also generates charged hydrophilic groups in solution, which is a crucial factor contributing to polymer swelling. The water absorption characteristics of SAP facilitate the regulation of early cement matrix hydration and ensure the long-term stability of the concrete structure. These attributes are crucial for maintaining stable development in cement hydration and ensuring the overall structural integrity over time. The knowledge gleaned from this review offers a robust framework for the further research work on SAP and serves as support for practical application of internally cured concrete in construction engineering that need to withstand challenging environmental conditions.

Sustainable utilization of phosphorus-rich sludge in cement composites: Multiscale evaluation and mechanistic analysis

The treatment of sludge poses challenges for resource utilization and environmental protection, and utilizing sludge as supplementary cementitious materials (SCMs) presents a viable solution. However, the phosphorus content significantly influences the cement hydration process. This study primarily investigates the feasibility of phosphorus-rich sludge (PRS) as SCMs and examines the effects of combining PRS with calcined clay on cement hydration. The research focuses on hydration heat, mechanical properties, microstructure, and durability of composites comprised of PRS, limestone, calcined clay, and ordinary Portland cement. The results indicate that PRS delays early hydration reactions, leading to a decrease in early compressive strength; after 7 days, the compressive strength is approximately 14.3 MPa (sample S20C10L15). However, over time, the strength increases to 34.1 MPa at 28 days, reflecting a 138.5 % increase compared to the 7-day compressive strength (with sample OPC exhibiting only 69.1 %). This correlates with the hydration exothermic peak occurring in the later stages and the transition of phosphorus's effect on cement hydration from inhibitory to non-inhibitory. The phosphorus in PRS partially replaces silicon atoms in C-(A)-S-H gel, forming C-S(A,P)-H gel. This process refines pore sizes within PRS cementitious materials, enhancing compressive strength over time. Early hydration inhibition and the subsequent pozzolanic reaction of PRS reduce portlandite content, which lowers carbonation durability and thermal expansion coefficient. However, the quaternary blend of PRS, limestone, calcined clay, and ordinary Portland cement demonstrates excellent mechanical properties. This study provides experimental evidence for reducing the environmental impact of PRS and exploring carbon reduction strategies in the cement industry.

Study on the mechanical property and durability of alkali-activated seawater and sea sand recycled aggregate concrete

This study investigates the potential of Alkali-Activated Seawater Sea Sand Recycled Aggregate Concrete (ASSRAC) as a novel sustainable construction material. By utilizing recycled aggregates from construction and demolition waste, seawater, sea sand, and alkali-activated materials such as fly ash and blast furnace slag, this innovative concrete aims to mitigate carbon emissions from cement production and optimize resource usage. The impact of recycled aggregate replacement rate, water-to-binder ratio, and sand type on the compressive strength of ASSRAC was examined through analysis of variance. Cylindrical axial compression and prism flexural tests were conducted to evaluate the long-term performance of ASSRAC under seawater immersion. The results indicate a decrease in compressive strength with higher recycled aggregate replacement rates and water-to-binder ratios, with recycled aggregates being the primary weak link. Additionally, increasing the water-to-binder ratio hampers hydration by diluting alkali activators, weakening polycondensation reactions. Under seawater immersion, ongoing reactions foster denser C-(A)-S-H structures, enhancing compressive strength and elastic modulus over time. Moreover, higher recycled aggregate replacement rates result in improved ductility, attributed to reactions between the old mortar on recycled aggregate surfaces and slag/fly ash at interfaces. For specimens immersed for 0 and 90 days, most theoretical models accurately predict results, except for the CEB-FIP model, which only accurately reflects the stress-strain curve at 180 days. The seawater-sea sand group's flexural strength initially exceeds that of the freshwater-river sand group due to accelerated early hydration, but this advantage diminishes over time due to high salt content.

Study on properties and CO2 emission of self-pulverizing calcium sulfoaluminate (SPCSA) after carbonization curing

The extensive use of Portland cement (OPC) has resulted in a steady rise in CO2 emissions from the construction industry, posing a significant climate threat. While adopting low-carbon cement enriched with belite minerals holds promise for substantial CO2 emission reduction in the cement industry, the limited early hydration activity of C2S constrains its engineering applications. Carbon capture, storage, and utilization (CCUS) technology, capable of rapidly developing the strength of C2S, opens up a new avenue for utilizing low-carbon cement. This study evaluated the properties of self-powdering calcium sulfoaluminate (SPCSA) cements with different C2S contents, and the carbon emissions during production and application were analyzed. The samples' carbonation area, compressive strength, and capillary water absorption properties were tested. The carbonation products and pore structures were also characterized using XRD, TGA, SEM, and Low-NMR. The results show that when the molar ratio of C4A3S̅ to C2S is 1:12 (S̅12), the compressive strength and CO2 sequestration of SPCSA are 69.78 MPa and 0.15 g/g, respectively. When CCUS technology is adopted, the CO2 emission during the production and application of SPCSA is 585.78 kg/t, much lower than that of OPC of 878.28 kg/t. This is significant as a reference for realizing carbon neutrality in the cement industry.

Effect of different amounts of barium substitution for calcium on the hydraulic activity of the high belite binary C2S-C4A3$ system

The substitution of Ba2+ for Ca2+ in both dicalcium silicate (C2S) and ye'elimite (C4A3$) has the potential to stimulate the development of early hydration activity of high belite sulfoaluminate cement (HBSAC). To relieve the emission pressure of CO2 in the cement industry and promote the early compressive strength development of HBSAC, the C2S-C4A3$ binary system with different amounts of Ba2+ substitution for Ca2+ was synthesized and investigated in this study. The SEM-EDS and XRD test methods confirmed the stoichiometric composition of Ba-bearing C2S-C4A3$ binary systems. The results showed that Ba2+ tends to preferentially replace Ca2+ in C4A3$ compared to replacing Ca2+ in C2S, resulting in more substitution amount of Ba2+ in C4A3$ mineral, as the designed substitution amount of barium increased from 25 wt.% to 55 wt.%, the stoichiometric formula of Ba-bearing C2S was transformed from Ca1.66Ba0.34SiO4 to Ca1.45Ba0.55SiO4, and the stoichiometric formula of Ba-bearing C4A3$ was transformed from Ca2.29Ba1.71Al6SO16 to Ca0.86Ba3.14Al6SO16. While excessive amount of barium (more than 45 wt.%) resulted in the increased content of by-products, such as BaSO4 and BaAl2O4, as well as the formation of C3S. The hydration properties of each group of synthetic clinker were investigated, including compressive strength, qualitative and quantitative analyses of the hydration products, leaching solution environment, and micromorphological analysis. The hydration products including C-(A)-S-H and AH3, as well as hydroxide (Ca(OH)2 and Ba(OH)2·8H2O), which can be carbonated to form carbonates (BaCO3 and CaCO3) by CO2 in the air. As the substitution amount of Ba2+ increased from 25 wt. % to 35 wt. %, the hydration degree of Ba-bearing α′L-C2S was promoted in the early stage, and the presence of C3S may affected the increase of early hydration activity of Ba-bearing α′L-C2S, however, the hydration degree of α′L-C2S with the most amount doping of barium in A055 samples exhibited the highest hydration degree of 88.0 % after hydration for 90 days. The compressive strength of high belite C2S-C4A3$ binary system of 3-day displayed a rapid increase from 8.6 MPa to 16.1 MPa, with the amount of barium increased from 25 wt. % to 55 wt. %. The compressive strength of A025 and A035 after hydration for 90 days increased steadily, reaching 35.0 MPa and 34.0 MPa respectively. However, the compressive strength of hydrated A045 and A055 samples for 90 days deteriorated and even cracked seriously for the hydrated A055 sample, which was attributed to the formation of a large amount of Ba(OH)2·8H2O and BaCO3 by excessive barium amount, and leading to the expansion and broken of the matrix. Thus, the designed amount of barium substitution for calcium in the C2S-C4A3$ binary system should be controlled, for a higher content of barium more than 35 wt. % could be damage to the development of the long-term hydration strength of the clinker. These results provided a theoretical basis to make it possible for the large-scale application of activated HBSAC, devoted to the sustainable development of infrastructure.

Influence Mechanism of Accelerator on the Hydration and Microstructural Properties of Portland Cement

Shotcrete is one of the most important types of concrete used in engineering construction, and its properties are significantly influenced by accelerators. This study investigates the effects of aluminum sulfate series alkali-free accelerator (AKF) and alkali accelerator (ALK) on the strength, hydration process, characteristic hydration products, and microstructure properties of shotcrete. Techniques such as setting time measurement, isothermal calorimetry, simultaneous thermal analysis, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDS), and mercury intrusion porosimetry (MIP) were utilized. The results indicate that both ALK and AKF significantly accelerate and increase the early hydration heat release rate and cumulative hydration heat of Portland cement, producing the characteristic hydration products hexagonal plate AFm and rod AFt, respectively. This acceleration notably speeds up the setting process of Portland cement. ALK negatively impacts the later-stage microstructural development and pore structure filling of hardened cement paste, leading to average reductions of 15.3% and 19.9% in flexural and compressive strengths at 28 days, respectively. Specifically, compared to ALK, AKF shows a faster hydration heat release rate during the induction period and a more significant increase in cumulative hydration heat during the hydration process; the cumulative hydration heat is on average 18.2% higher than AKF. Furthermore, AKF does not hinder the subsequent C3S hydration and C-S-H gel densification process. After 28 days of curing, EDS analysis indicates an average Ca/Si ratio of 1.171 for the AKF-treated shotcrete; the average Ca/Si ratio shows minimal variation from the reference group and is classified as the same type of C-S-H gel as the reference group. Therefore, the strength of hardened cement paste with AKF continues to increase steadily in the later stages. At 28 days, the average flexural strength increased by 10.2%, while the compressive strength decreased by only 3.0%. These findings suggest that AKF enhances the microstructural development and strength of shotcrete, making it a more effective accelerator for engineering applications.

Clarifying early period hydration process of ultra‐low W/B cementitious composite subjected to underwater circumstance

AbstractAn innovative method is proposed in this study that combines long sequence precision prediction model with experiments to study how early hydration affects ultra‐low water‐binder ratio cementitious composite (ULWBRCC) properties. To be specific, by using heat release and degree of hydration as variables and introducing various temporal models to analyze the early hydration process, the micro‐ and macroscopic properties of specimens at different ages are assessed in detail. The obtained results can be summarized as follows: The long‐sequence accurate time series model can predict the earliest hydration process of underwater ULWBRCC, and the predicted late‐stage hydration pattern matches the experimental results. The underwater environment optimizes ULWBRCC's hydration process and increases its early compressive strength by 19.6%. The hydration of ULWBRCC is predicted using a time series model in the paper, filling the gap of uncertainty in the earliest performance of underwater rapid repair cement‐based composite materials, and the MSE of the Informer is improved by 92.88% compared with other models.

Solubility-controlled early age hydration of carbonate-activated slag: Underlying mechanisms and acceleration via seeding

The low environmental impacts and good performance of carbonate-activated binders have attracted substantial interest, while their intrinsically delayed reaction and prolonged setting times constrain widespread implementation. This study aims to investigate the early-age reaction kinetics of carbonate-activated binders, elucidate the underlying mechanisms and propose controlling methods. Results reveal that hydrotalcite and C-A-S-H gel precursors rapidly reach supersaturation within hours, yet precipitation of these phases remains absent. This phenomenon, coupled with high Si/Ca ratios in the pore solution, exhibits characteristics that may contribute to the observed reaction delays. A prolonged induction period and lethargic strength development are observed owing to the lack of strength-giving phases. The hydrotalcite and C-A-S-H concentrations surpass their theoretical solubility thresholds due to rising ionic strength and salt-in effects. The addition of a pH-neutral layered double hydroxide salt accelerates the reaction, confirming seeding impacts control pore solution saturation limits, constituting the underlying accelerator mechanism.

Bamboo fiber-enhanced UHPC: Early hydration and microstructural/mesoscale analysis

This study investigates the impact of incorporating bamboo fibers, a natural and renewable material, into ultra-high performance concrete (UHPC) on its early hydration, mechanical properties, internal relative humidity, autogenous shrinkage, and microstructure. The results show that adding bamboo fibers significantly improves various UHPC properties. Bamboo fibers regulate hydration and prolong the hydration process through their water absorption and retention abilities. With a fiber content of 1.0 vol percent (vol%), the compressive strength increases by 10.2 %, reaching 97.1 MPa, and at 2.0 vol%, flexural strength and toughness increase by 37.9 % and 739.5 %, respectively. Additionally, bamboo fibers help maintain internal relative humidity above 98 % during the first 7 days of curing and reduce autogenous shrinkage by up to 55.9 %. The fibers also optimize the microstructure by minimizing voids, with a 1.0 % fiber content reducing the void ratio to 1.64 %. This reduces large voids and improves the material's density. Overall, bamboo fibers show great promise in enhancing UHPC's structural performance and environmental adaptability while being a sustainable and cost-effective material.

Synergistic enhancement of g-C3N4/CoAl-LDH nanoflower and mineral admixtures on the properties of nano-engineered cementitious composites

The nano-engineered cementitious composites (NCC) were prepared using g-C3N4/CoAl-LDH nanoflower (nano-CN/L), in combination with mineral admixtures including fly ash (FA), metakaolin (MK), and ground granulated blast furnace slag (GGBFS). The synergistic effects and mechanisms of nano-CN/L and mineral admixtures on the mechanical, chloride penetration resistance and air purification properties of NCC were investigated. The results show that nano-CN/L promotes the early hydration of cementitious materials and improves the composition and morphology of C-S-H gel. Furthermore, the filling effect of nano-CN/L significantly optimizes the pore structure and interfacial crack width of NCC, thereby eliminating the adverse impact of FA, MK, and GGBFS on its early mechanical strengths. Additionally, nano-CN/L enhances the chloride penetration resistance and NOx removal properties of NCC through its strong ion adsorption and photocatalytic activity, respectively. Incorporating 0.9 % nano-CN/L by mass of cementitious materials reduces the chloride diffusion coefficient of NCC at curing age of 56d by 26.9 % and increases the NOx removal ratio by 11 times. The 7d’s compressive and flexural strengths of NCC increase by 13.6 % and 4.6 %, respectively, compared to the one without nano-CN/L. As a novel multifunctional nanomaterial, nano-CN/L not only provides a new pathway for extending the service life of cementitious composites, but also injects new momentum into their environmental-friendly development.