Wet carbonation of calcium-rich solid wastes to produce Supplementary Cementitious Materials (SCMs) has gained research attention. This study investigates a capture-mineralization approach using monoethanolamine (MEA), diethanolamine (DEA), and triethanolamine (TEA) to enhance carbonation of recycled cement powder (RCP). The novelty lies in exploiting the dual alkalinity and complexation capability of alkanolamines to overcome the kinetic bottlenecks of CO2 transport and Ca2+ leaching. Results show alkanolamine solutions significantly accelerate carbonation, achieving a final degree of 64.8% within 60 min, compared to 56.4% with pure water. At 10 min, DEA reached 57.2%, versus 39.3% conventionally. The hydration induction period of cement mortars incorporating modified RCP was shortened by 1.2–2.4 h, with DEA exhibiting the most pronounced catalytic effect, attributed to calcite nucleation sites and reactive silica gel. This modified RCP accelerates early-age hydration and enhances early strength compared to untreated RCP, offering a viable sustainable option for cement replacement.

Recycled powder (RP) is a by-product generated during the crushing process of construction and demolition waste for the production of recycled aggregate. The potential of using RP as a supplementary cementitious material (SCM) has not been widely investigated, which is due to its low activity and high-water demand. This article analyzes the physical properties, chemical composition of RP, and its influence on the hydration process. The effects of RP used as an SCM and sand replacement on the workability, microstructure, mechanical properties, and durability of concrete have been conducted. RP exhibits a pozzolanic activity index range of 50% to 85%. The relative strength is higher than 0.8 when the replacement ratio of RP is below 20%. The utilization of RP as an SCM or sand replacement could be a potential technique for developing sustainable cement-based materials. This strategy could reduce the quantity of natural resources and carbon emissions in the concrete industry.

This study examines the flexural behavior of seawater sea sand high-performance concrete (SWSSHPC) reinforced with polypropylene fibers (PPF), sisal fibers (SSF), and their hybrid combination. Fiber type, volume fraction (0.5%, 1.0%, 1.5%), and length (5, 10, 15 mm) were evaluated in a unified experimental program. Compressive strength, three-point bending, flowability, and microstructure were assessed using FTIR, XRD, and SEM. Fiber addition increased flexural strength by about 16–79% compared with the plain mix. The highest gain, 79.3%, was achieved with SSF at 0.5% and 5 mm, while the best PPF mix reached 59.9% at 1.0% and 5 mm. Hybrid fibers produced more stable flexural performance and the greatest deformation capacity. Compressive strength showed a weaker response, with gains up to 23.6%. Microstructural analysis showed stronger SSF matrix interaction than PPF matrix. A regression model predicted flexural strength accurately (R2 = 0.915).

This study examines the influence of wind intensity on mixture behavior, forming quality, mechanical performance, hydration characteristics and interfacial transition zone (ITZ) of roller-compacted concrete (RCC). Meanwhile, the formation mechanism of its spatial variability is revealed through the probabilistic statistical analysis of compressive constitutive parameters. The results show that wind disturbances cause surface RCC to present increased VC values, more surface pitting, inhibited hydration and pozzolanic reactions, and reduced microhardness and compressive strength. Especially, force-9 wind increases 123.7% in porosity and 174.8% in thickness of the ITZ. With enhancing wind force, AFt tends to convert to carbonoaluminates and the reaction degree of C3A and C4AF decreases by up to 10%, exhibiting higher wind sensitivity. Statistically, the spatial variability is transmitted across scales and amplified along the thickness direction under high wind-force level, ultimately increasing the coefficients of variation of elastic modulus and peak strain by 4.8 and 2.7 times, respectively.

Concrete has high compressive strength but limited tensile capacity and deformation, leading to brittle failure. This study extends the Triangular Plate Method (TPM), originally developed for cement-based materials, to steel fiber-reinforced concrete (SFRC) and validates it against the EN 14651:2005 + A1:2007 three-point bending (TPB) test. Plain and fiber-reinforced concretes containing hooked-end steel fibers at 0.3%, 0.6%, and 0.9% were tested using equilateral triangular plates and notched beams. Load-displacement responses were used to evaluate tensile strength, ductility, and toughness. The results show that steel fibers have a limited effect on compressive strength but markedly improve post-cracking stability, tensile performance and energy absorption, particularly at fiber contents of 0.6% and above. The strong correlation between TPM and TPB toughness values demonstrates that TPM can reliably assess SFRC under biaxial bending-type stress conditions and support practical evaluation of plate-like fiber-reinforced cementitious elements.

The weak interfacial transition zone (ITZ) and high porosity of recycled coarse aggregates (RCA) limit their use in structural concrete. A sequential triple-treatment: HCl chemical treatment, mechanical abrasion, and cement slurry coating, was developed to densify the ITZ. Testing 198 specimens across six mix designs (0–100% RCA), TTRCA at 25% and 50% retained 92.1% and 87.3% of compressive strength, 93.6% and 87.7% of flexural strength, and 95.6% and 89.9% of splitting tensile strength versus the NCA control. Resistivity reached 81–91% of control; shrinkage remained 8–18% above control. XRD confirmed reduced Ca(OH)2 content with enhanced C–S–H formation; SEM revealed reduced ITZ porosity. ITZ densification was identified as the primary governing mechanism, supported by microstructural, mechanical, and durability evidence. Statistical analysis confirmed significant treatment effects (ANOVA, p < 0.001). A critical 50% replacement threshold was established, supporting regulatory RCA limit revision and circular economy goals.

The discovery of the feasibility of using activated clays to produce reactive aluminosilicates has significantly expanded the raw material base for supplementary cementitious materials, opening up new prospects and options for low-carbon cements. Furthermore, the potential of kaolin clays for producing pozzolans has been thoroughly studied and practically realized. However, the more widely available and accessible non-kaolin clays of the 2:1 structural type require further comprehensive studies of their suitability in relation to the variety of influencing factors. In this study, the reactivity of five montmorillonite clays calcined at 830 °C and milled to Dv,50 of 11.5–13.8 µm was explored through chemical, mechanical, and thermal methods. Based on the consistency of results obtained through these techniques insights into the relationship between the reactivity of low-, medium, and high-grade montmorillonite clays and their chemical/mineralogical composition are presented. These findings advance the understanding of the categorization of montmorillonite clays as supplementary cementitious materials.

Silica fume (SF) is widely used to improve concrete strength and durability; however, in practice it is often supplied in densified form, producing agglomerates that may not fully disperse during mixing. Although coarse SF agglomerates can act as localized sources of reactive silica and promote alkali–silica reaction (ASR), their effect on concrete mechanical and durability performance remains unclear. This study investigates whether the agglomeration of commercially densified SF can decouple conventional durability indicators from ASR mitigation. Three densified SF grades, moderate, large, and very large were evaluated. Concrete and mortar performance was assessed through compressive strength, water-permeability, chloride-ion penetrability and sulfate resistance. ASR susceptibility was examined by accelerated mortar bar testing, and damage was characterized by petrography and SEM. All SF mixtures improved conventional performance, but ASR response was strongly dependent on agglomerate size and dosage. These findings identify agglomerate-size distribution as a key qualification parameter for commercially densified SF.

With the rapid development of structural health monitoring, intelligence has become an important trend in cement-based materials. Recycled carbon fibers (RCF) feature favorable electrical conductivity. This study investigates the effects of varying fiber contents on the piezoresistive properties of cement mortar. The relationship between electrical signals and stress under failure and cyclic loading was analyzed. Piezoresistive performance was evaluated in terms of linearity, sensitivity, repeatability, and hysteresis, and the damage-sensing capacity was explored via acoustic emission tests. The results reveal that the incorporation of RCF significantly enhances the piezoresistive properties of cement mortar, exhibiting a favorable linear correlation between the fractional change in resistance and stress. Acoustic emission signals and resistivity variations can effectively characterize the internal damage evolution of mortar. Under cyclic loading, recycled carbon fiber cement mortar (RCFCM) presents good repeatability and stability. With rising loading amplitude, the irreversible damage of the conductive network aggravates, and the hysteresis effect increases.