While environmentally beneficial, recycled fine aggregates (RFA) are limited by high porosity and poor interfacial properties, which also aggravate segregation behavior in lightweight expanded polystyrene (EPS) concrete. To synergistically address these dual challenges, this study provides the first systematic investigation of carbonation pretreatment (0.1-0.4 MPa, 12-48 h) for modifying RFA tailored specifically to EPS concrete applications. The effects were evaluated through a comprehensive approach that integrated a newly developed ultrasonic pulse velocity-density model with image analysis, allowing for the quantification of EPS spatial uniformity, a key methodological innovation in this study. Results show that optimal carbonation conditions (0.4 MPa, 48 h) reduced RFA water absorption by up to 31.7 % while increasing aggregate density by 5.6 %, improving concrete workability and enhanced compressive strength by up to 15.3 % at a 50 % replacement level. Notably, a nonlinear "reaction inhibition effect" was identified, indicating that excessive surface densification can constrain further treatment efficiency. Carbonated RFA substantially improved EPS spatial uniformity, reducing segregation indices by 46-52 %, as validated by the proposed quantitative model. Overall, this work demonstrates a synergistic waste-to-resource strategy, in which carbonated RFA simultaneously enhances both the mechanical performance and uniformity of lightweight EPS concrete, contributing to the development of advanced low-carbon construction materials.

Corrosion of steel reinforcement in chloride-contaminated concrete poses a significant threat to infrastructure durability. To address this, an environmentally friendly tannic acid-phytic acid composite conversion coating (TA-PACC) was developed for carbon steel. The coating was formed through a sequential immersion process, and its formation mechanism, tailored by processing time, was elucidated using SEM, EDS, AFM, FT-IR, and XPS. The results reveal that a 10-minute treatment yields an optimal, uniform monolayer (similar to 16 mu m thick) with the lowest surface roughness, attributable to the effective sealing of inherent micropores in the initial tannic acid layer by phytic acid complexes. Consequently, this coating achieved exceptional corrosion protection, with an efficiency of 99.90% after 7 days in a chloride-containing simulated concrete pore solution. Conversely, prolonged treatment (30 min) induced cracking due to excessive hydrogen evolution and interfacial stress, drastically reducing the protection efficiency to a mere 12%. This work underscores the critical role of processing time in designing high-performance conversion coatings and provides a fundamental basis for their application in alkaline concrete environments.

Chloride ions are primary factors in metal corrosion in marine environments. Layered double hydroxides (LDHs) are widely used in corrosion protection due to their anion-exchange properties. However, conventional LDHs have low selectivity for chloride ion exchange and unsatisfactory adsorption and immobilization efficiency. So, enhancing LDHs' adsorption and immobilization ability for chloride ions is a research frontier in metal corrosion protection. Metal-organic frameworks (MOFs), characterized by exceptional adsorption capacity, extremely high specific surface area, and abundant active sites, have found broad applications in separation, catalysis, and corrosion prevention. Consequently, combining MOFs with LDHs to harness their complementary advantages for improving chloride ion adsorption and immobilization efficiency holds promising research prospects.In this study, a Zn-Al-LDH@ZIF-8 composite material was successfully prepared via an in-situ synthesis method. Its adsorption performance was investigated through chloride ion titration, adsorption kinetics, and adsorption thermodynamics. Furthermore, the immobilization mechanism of chloride ions was examined by means of scanning electron microscopy, X-ray diffraction, infrared spectroscopy, and specific surface area analysis. The results demonstrated that the composite exhibited a maximum adsorption capacity of 66.25 mg/g, which was significantly higher than that of single-component materials, while showing optimal structural stability and adsorption efficiency under neutral conditions. The superior performance of the composite can be attributed to the synergistic effect of Zn-Al-LDH's interlayer anion-exchange capability and ZIF-8's high surface area and microporous structure. Additionally, temperature and pH regulation experiments indicated that 25 degrees C and a neutral environment represented the optimal adsorption conditions, further confirming the material's potential for practical applications.

Autogenous shrinkage is one of the important factors affecting early-age cracking of concrete face slabs in rockfill dams. Carbon nanotubes (CNTs) possess excellent potential to enhance the performance of face slab concrete. The autogenous shrinkage behavior of CNTs-modified face slab concrete urgently requires investigation. Currently, studies on the effect of temperature on autogenous shrinkage often focus on a single temperature condition. To address this limitation, this study investigates the effects of different curing temperatures (20 degrees C, 30 degrees C, and 40 degrees C) and CNT dosages (0%, 0.03%, 0.06%, 0.10%, and 0.15%) using cement paste. The results showed that an increase in curing temperature significantly accelerates the early-age autogenous shrinkage rate, particularly within the first 24 h, and also intensifies the ultimate shrinkage magnitude. Similarly, a higher CNT content was found to enhance both the development speed and the final value of early-age autogenous shrinkage. Furthermore, a multiscale model for early-age autogenous shrinkage of cement paste was established by integrating continuum micromechanics with capillary pressure theory, which provided good agreement with the experimental data. The results showed that chemical shrinkage in the unsaturated humidity stage is driven by capillary pressure. Moreover, the model indicates that chemical shrinkage accounts for the majority of autogenous shrinkage, approximately over 70% of the total. It also reveals that the effects of temperature and CNTs on autogenous shrinkage primarily manifest through accelerated early-age cement hydration, increased chemical shrinkage during the humidity-saturated phase, and the prolonged duration of this phase.

Carbon nanotubes-(CNTs) play a crucial role in enhancing the crack resistance of cementitious material, especially for mass concrete structures. However, the crack-bridging effect of CNTs remains unclear under different internal relative humidity (RH) conditions. In the present work, three-point bending experiments, molecular dynamics (MD) simulations, and theoretical analysis were systematically applied to investigate the crack-bridging effect of CNTs on cement composites. The results indicated that the crack-bridging effect of CNTs was highly dependent on RH and was primarily reflected by their strengthening and toughening contributions. With increasing RH, CNTs reinforced the Calcium-Silicate-Hydrate (C-S-H) system primarily by inducing structural compaction of the interlayer regions through water migration and silicate chain rearrangement. In contrast, the toughening effect was progressively suppressed as a continuous water film formed at the CNT/C-S-H interface, lubricating the interfacial interaction and weakening crack-bridging capability during crack propagation. Moreover, the fracture toughness of the CNT/C-S-H system was theoretically evaluated using Irwin formula, which bridged MD simulation results with macroscopic mechanical properties. Overall, this study identified an optimal humidity condition (RH ≈70%) where the strengthening and toughening effects of CNTs operate synergistically. These insights provide a theoretical foundation for the rational design of CNT-reinforced cementitious composites from a nanoscale perspective.

Nanocellulose, a nanostructured cellulose with high modulus, large specific surface area, and excellent mechanical properties, has shown great potential in cementitious materials. This study first presents a bibliometric analysis of research on nanocellulose-modified cementitious materials and then comprehensively reviews four nanocellulose types, namely, cellulose nanofibers, cellulose nanocrystals, bacterial cellulose, and cellulose filaments. Their effects on the mechanical performance, hydration, shrinkage, rheological behaviour, microstructure, and durability of cementitious materials are compared and discussed. The results indicate that different nanocellulose types influence cementitious materials in different ways. Appropriate incorporation of nanocellulose, together with suitable mixture parameters such as water-to-cement ratio, supplementary cementitious materials, and mix design, can effectively improve the mechanical, rheological, and durability-related properties of cementitious composites. Finally, promising application scenarios, such as oil well cement and dental materials, are highlighted, while major technical bottlenecks, including dispersion difficulties caused by nanoscale agglomeration and alkaline instability due to glycosidic bond hydrolysis, are discussed.

With the growing depletion of natural sand resources, manufactured sand has been increasingly adopted in concrete production. However, the clay content in manufactured sand, especially montmorillonite (MMT), severely impairs the workability and mechanical properties of concrete due to its strong water absorption and high affinity for polycarboxylate superplasticizer (PCE). To address this issue, this study elucidates the role of polyethylene glycol (PEG) in a cement-MMT system incorporating PCE and investigates its underlying triggering mechanism. The effects of PEG on the workability, hydration behavior, and microstructural evolution of the system are systematically examined. Additionally, the triggering mechanism of PEG's action in MMT is revealed by means of molecular dynamics methods. The findings suggest that the appropriate incorporation of PEG can enhance both the workability and compressive strength of the cement-MMT paste. Compared with the sample without PEG, when the PEG dosage is 0.50%, the enhancement rates of the compressive strength of the hardened paste at 3 d and 28 d reach 25.0% and 16.1%, respectively. A further analysis of the impact of PEG on the hydration shows that its incorporation significantly accelerates water consumption in the system. Although it does not alter the fundamental stages of the hydration process, it substantially promotes the hydration kinetics. Specifically, this results in a rise of C-S-H gel content by approximately 12.88% and a distinct elevation in the polymerization degree of silicate chains. In terms of triggering mechanism, PCE begins to adsorb between the MMT layers at 7500 ps, while the binding time of PEG to the interlayer sites of MMT is significantly reduced to 1350 ps. By 7500 ps, PEG has completely occupied the interlayer sites of MMT, effectively preventing PCE from adsorbing on MMT. This phenomenon avoids the loss of PCE's effectiveness due to its adsorption on MMT, ensuring that PCE can fully exert its dispersing effect on cement particles, thus optimizing the workability and hydration behavior of the paste.

Although CO2 curing of cement-based materials offers a promising pathway for carbon capture, utilization, and storage (CCUS), the multiscale regulation of porosity on CO2 curing in aerated concrete is not well understood, limiting the optimization of this technology for carbon sequestration and performance. This study aims to investigate the influence of porosity on the CO2 curing behavior of aerated concrete with dry densities ranging from 550 to 850 kg/m3. Through macro-and micro-scale analyses, including compressive strength tests, XRD, FTIR, TG, SEM, BET, and X-CT, the evolution of strength, phase composition, carbonation depth, and pore structure was investigated. Results show that mass gain after CO2 curing exhibits a decreasing trend with increasing dry density, following a negative power relationship, with the lowest density specimen (550 kg/m3) achieving a 9.7% increase. Early-age strength was enhanced by 4-29% after CO2 curing, although later strength development was moderately inhibited. After 5 h of carbonation, the degree of carbonation at the maximum depth decreased with increasing density-from 77.1% in low-density samples to 52.1% in high-density samples-as small pores constrained CO2 diffusion and permeation. Pore structure analysis showed that total pore volume in low-density specimens was approximately 4.5 times that of high-density specimens, and CO2 curing reduced porosity by up to 3.2% through pore filling and segmentation, particularly in pores below 0.2 mm. The study elucidates the porosity-dependent mechanisms of CO2 diffusion and product formation, providing a theoretical basis for efficient carbon sequestration and performance assurance in aerated concrete.

In the contemporary construction industry, the efficient utilization of solid wastes and the pursuit of low-carbon development have emerged as critical challenges. To address the challenge of utilizing low-reactivity lithium slag (LS), this study used LS as a precursor, combined with ground granulated blast furnace slag (GGBS) and fly ash (FA), to develop a novel ternary alkali-activated material (AAM) system. Multiple mixes of GGBS, FA, and LS were prepared and tested for fresh, mechanical, and microstructural properties, along with cost and environmental assessments. The experimental results showed that the mix with a GGBS:FA:LS mass ratio of 5:3:2 achieved the highest compressive strength. Specifically, compared with the reference sample without LS, the strength enhancement rates at 3 d and 28 d were 102.0 % and 22.8 %, respectively. This is because the incorporation of LS promotes the hydration of AAM and enhances the structural density. After achieving excellent mechanical performance, from a cost perspective, ternary AAM systems fabricated using LS also exhibit significant cost advantages. Under the condition of optimal compressive strength, an impressive energy savings of 190 MJ and a substantial carbon footprint reduction of 24.90 % were achieved. This work reveals that in the AAM system, LS synergistically interacts with GGBS and FA. The GGBS:FA:LS = 5:3:2 mix is an optimized and validated option, offering valuable insights for solid-waste utilization and low-carbon construction development.

Using subsea tunnel spoil aggregate (STSA) in concrete alleviates natural sand and gravel shortages while promoting excavation waste recycling. However, inherent chloride ions in STSA act as an internal chloride source, risking the long-term durability of concrete structures. To clarify STSA chloride release behavior, leaching tests were conducted in a simulated concrete pore solution (saturated Ca(OH)2). The effects of aggregate lithology, particle size, and temperature on leaching were investigated, with mechanisms analyzed via MIP, XRD, FTIR, and SEM. Results indicate lithology primarily controls leaching behavior. Although the initial free chloride content of diabase was 41.7% higher than granite, its 56-day cumulative leaching was only 27.2%-57.1% of granite's. Granite exhibited rapid early-stage leaching, releasing 82.0% of its 56-day total within the first 3 days, whereas diabase released only 41.0%, demonstrating a more sustained process. A pseudo-second-order kinetic model well-described the leaching process for both aggregates. Furthermore, particle size and temperature had limited influence on granite. Conversely, diabase leaching increased with smaller particle sizes and showed a non-monotonic temperature response: its 56-day leaching amount dropped from 18.60 mg/L at 20 degrees C to 12.83 mg/ L at 40 degrees C, but surged to 30.30 mg/L at 60 degrees C. This indicates that chloride leaching from diabase is jointly governed by temperature-dependent dissolution-precipitation processes and pore-structure evolution. This study provides theoretical support for the safe utilization of STSA in concrete engineering.

The carbonation reaction rate (CRR) and fineness of steel slag (SS) are critical factors influencing its CO2 sequestration rate (CO2 SR). This study employs a wet carbonation method and N-methyl diethanolamine (MDEA) to enhance the CRR of SS and synthesises nanoscale carbonated steel slag powder (CSSP). Results showed that MDEA increased the CRR by 117.9% and enhanced specific surface area and pore volume by nearly 50 times. The carbonation process of SS proceeds through four stages: CO2 absorption and activation, metal ion release, carbonate directional crystallisation, and co-growth of calcium-silicate-hydrate (C-S-H) gel with carbonates. MDEA facilitates the transformation of spherical or needle-shaped aragonite CaCO3(a) on the surface of SS into more stable, porous, cauliflower-like calcite CaCO3(c). The resulting nanoscale CSSP exhibits potential for application as an adsorbent in wastewater treatment.

Recycled carbon fiber (RCF) is a promising material for cementitious composites owing to its exceptional properties. However, the existing evaluation criteria for the comprehensive benefits of recycled carbon fiber reinforced cementitious materials are yet to be fully established. This study developed a multi-criteria benefit evaluation framework for RCF-reinforced mortar based on hybrid weighting methodology. A hybrid weighting model incorporating Analytic Hierarchy Process (AHP) and Entropy Weight Method was employed to assign weights to performance, environmental, and economic indicators, which ensured equilibrium between expert judgment and objective data. Besides, comparative studies were performed using virgin carbon fiber (VCF) and polyvinyl alcohol (PVA) fiber as reference systems, enabling direct performance comparisons. The results demonstrated that the flexural, tensile and splitting tensile strength of RCF-reinforced mortar increased 20.3 %, 35.5 % and 44.6 % than mortar without fiber, respectively. The RCF-reinforced mortar achieved a 19 % higher integrated benefit index than mortar without fiber. These findings confirm that RCF constitute a sustainable construction material exhibiting significant engineering potential.

This paper aims to investigate the mechanism of the effect of recycled carbon fibers on the fracture toughness of cement mortar and assess their environmental impact. The physical and interfacial properties of RCF were first characterized and found comparable to those of virgin carbon fibers (VCF). Three-point bending tests revealed that RCF significantly enhances the fracture energy, ductility index, crack initiation toughness, unstable toughness and cohesive toughness of cement mortar by up to 446.84 %, 238.71 %, 104.22 %, 137.12 % and 169.09 %, respectively. Additionally, the bilinear softening constitutive curve for recycled carbon fibers reinforced cement mortar was applied to compute the cohesive toughness which was validated by experiments and the related research on virgin carbon fibers reinforced cement mortar was conducted for comparison. Finally, a strength-based life cycle assessment showed that the global warming potential and primary energy depletion indicators of RCF-reinforced mortar were reduced by 38.47 % and 13.79 %, respectively, compared to VCF-reinforced mortar. These results confirm the engineering feasibility and sustainability of using RCF as a substitute for VCF in cement mortar.

Bischofite (MgCl26H2O), the byproduct of salt lake resource extraction, is a useful source for valuable resources. This study investigated the production and utilization of reactive magnesia (MgO) cement (RMC) from bischofite. Synthetic RMC recovered through timed calcination was used in preparing CO2-cured mortars and compared to samples produced from commercial RMC. The acid neutralization time, an indication of reactivity, of the synthetic RMC from complete calcination indicated a good correlation with the specific surface area. Synthetic RMC-based mortars exhibited higher reaction rates of hydration and carbonation than mortars involving commercial RMC. Furthermore, mortars prepared with synthetic RMC demonstrated higher compressive strengths, attributed to a denser pore structure and enhanced moduli/hardness in interfacial transition zones. The identification of the key factors governing mechanical performance facilitated the regulation of the strength of high-activity RMC-based mortars. The overall CO2 per MPa of the synthetic MgO-based mortar was 19.7% lower than that for the commercial RMC-based mortar.

Lithium slag (LS), rich in S, Al, and Si, is promising for expansive agents (EA), yet its influence mechanism in cement-based materials remains unclear. In this study, a novel lithium slag expansive agent (LS-EA) was developed using LS, anhydrite, and calcined CaO. The effects of LS content, CaO activity, and anhydrite/CaO ratio on performance of mortar containing 10 wt% LS-EA was evaluated by the orthogonal design. Optimized LS-EA (L55S25C20, L55S15C30, L65S15C20) were selected to compare with commercial EA (UEA, HP-CSA). Results show anhydrite/CaO ratio most significantly impacted restrained expansion rate. Meanwhile, calcining CaO at 1350 degrees C for 1 h optimally delayed hydration, maximizing expansion. Optimal group L55S15C30 reduced 28 d drying shrinkage by 31.2 % and decreased cracking area density by 48.2 % due to enhanced AFt and Ca(OH)2 formation and denser microstructure. Overall, a higher restrained expansion rate of EA correlated with better deformation control, crack resistance, and durability of mortar. LS-EA performance matched commercial HP-CSA, superior to commercial UEA. This study provides a theoretical basis for the application of LS in EA to enhance the deformation control and crack resistance of mortar.

Solid waste steel slag (SS) has a limited carbonation degree. MDEA was used to accelerate the carbonation of SS fine aggregate in this study, and mortars were prepared by using uncarbonated/carbonated SS fine aggregate to replace 50 % natural sand. The results showed that MDEA promoted the dissolution of Ca2 + in SS and accelerated the carbonation of SS. At the 10 wt% MDEA, SS exhibited the highest carbonation degree (33 % higher than carbonated SS without MDEA). However, excessive MDEA led to hindered COQ transfer efficiency, resulting in a decreased carbonation degree. Meanwhile, CO2 treatment significantly improved the volume stability of SS, with autoclave expansion rate of 0.13 %-0.29 %. Moreover, owing to carbonated enhanced SS, better pore structure and ITZ performance in mortar, the strength of carbonated SS fine aggregate-based mortar was enhanced. MM10SS group revealed the largest 28 d compressive strength (37 % higher than group with natural sand). This study paves the way for using MDEA to accelerate the carbonation of SS and enhance its mechanical property and volume stability in mortar.

This study explores the feasibility of incorporating copper slag (CS) as a partial mineral precursor in alkaliactivated materials (AAM). By utilizing ground granulated blast furnace slag (GGBS), fly ash (FA), and CS as precursors, a novel three component eco-friendly binder has been successfully developed. The study comprehensively assesses the influence of CS on the reaction rate, microstructural feature, and environment impact of AAM system. Compared to FA, CS exhibits higher solubility of silica and calcium, which can participate more effectively in geopolymerization and play a notable role in the formation of C-(A)-S-H gels. A K-D model was constructed using heat release data, revealing that the addition of CS significantly enhances the reaction extent. This led to a 33.3 % increase in the compressive strength of the matrix at 3 d and a notable enhancement in the degree of polymerization of the gel network. Microstructural analysis demonstrates that increasing CS substitution improves gel enrichment and pore filling effects. This optimization of the pore structure resulted in a decrease in both porosity and the quantity of large sized pores. From an economic and environmental perspective, reusing CS brings about a substantial decline in both energy consumption and carbon emissions, achieving a 56.92 % decrease in energy consumption and a 75.81 % reduction in carbon emissions. Such work may shed valuable insights to the recycling of various types of solid waste and low-carbonation of building field.

Mineral carbonation of civil engineering materials (MC-CEM) has received increased attention in reducing CO2 emissions. This work comprehensively describes the research trends and hotspots in MC-CEM based on bibliometric analysis. Articles were collected in the Web of Science core database from 2001 to 2024 and analyzed in detail. The results show that MC-CEM is a hot research topic, with hot-topic words changing quickly. China and Switzerland reveal the most publications and the highest average citations, respectively. Under carbonation curing, the strength and durability are usually improved due to carbonate formation. Concerning CO2 storage capacity, carbide slag, reactive magnesium oxide cement, and β-C2S are active, while fly ash, mine tailings, and carbon mix are inactive. Slow kinetics and low carbonation influence the large-scale industrial application of MC-CEM. Finally, challenges and prospects in MC-CEM are illustrated. In future studies, it is necessary to enhance the CO2 sequestration capacity by investigating the carbonation mechanisms and optimizing the process parameters. A comprehensive life-cycle assessment of MC-CEM is also needed. This work provides the basis for the development of large-scale mineral carbonation by using civil engineering materials.