Assessing the risk of alkali-silica reaction (ASR) in large-scale concrete structures remains a critical challenge, particularly due to the scarcity of field-based data and the long timescales involved. This study proposes a methodology to evaluate ASR risk in concrete containing slowly dissolving aggregates. The approach consists of three steps: (i) identifying material properties such as the dissolution rate and chemical composition of the dissolved phases; (ii) determining the critical reaction degree at which amorphous silica forms, using equilibrium calculations based on GEMS thermodynamic simulations; and (iii) estimating the time required to reach this threshold by solving coupled equations for moisture transport and aggregate dissolution under real structural conditions. The methodology is demonstrated using in-situ data from the aged concrete walls of the Hamaoka nuclear power plant. Key factors that mitigate ASR risk are identified, including low dissolution rates, water depletion over time, and the presence of stabilizing species such as Al₂O₃ and MgO in the dissolved phase. While developed for a specific case, the proposed approach provides an adaptable framework for rational ASR risk evaluation in existing and future concrete structures.

3D concrete printing (3DcP) offers a transformative approach to modern construction, providing unique benefits such as faster construction, lower labour costs, and minimal material waste. Despite these advantages, high cement consumption and the challenge of achieving conflicting rheological requirements limit its widespread application. This study addresses these challenges by developing an Ordinary Portland Cement (OPC)-based 3D printable mortar incorporating magnesium oxide (MgO) as a partial cement replacement and using carbonated water (CW) as the mixing water. MgO is an abundant material capable of reacting with CO₂ to form stable carbonates, while CW promotes early hydration and carbonation. Unlike previous approaches that require hydration agents to overcome the low dissolution of MgO, this work combines MgO and CW to meet the rheological demands of 3DcP without additional additives. Rheological properties such as static yield stress, buildability, and workability were evaluated alongside compressive strength and microstructural characteristics using XRD, SEM, TGA, and FTIR analyses. Results showed that MgO increased static yield stress due to higher water absorption, while CW further enhanced it through accelerated hydration. The MgO-CW combinations, particularly mixes with 25% (25MCW) and 50% MgO (50MCW), exhibited yield stress increases of 505% and 425%, respectively, after 30 minutes compared to a control mix with pure water (CPW). Among the tested mixes, 25MCW achieves a practical balance of extrudability, buildability and compressive strength, confirming its applicability for 3D printing applications under the tested conditions. Moreover, microstructural analysis confirms enhanced hydration and carbonation reactions in the MgO-CW modified mix, which contribute to the improved performance of the developed sustainable material. This study offers insights for advancing eco-friendly 3D printable materials and sustainable construction.

In cold climates, the durability of construction materials against freeze-thaw cycles is critical for ensuring long-term structural safety. To minimize environmental impact, blast furnace slag cement, incorporating varying proportions of blast-furnace slag fines, is increasingly being adopted as a sustainable alternative to ordinary cement. While the freeze-thaw resistance of such materials has been widely studied, their performance after repeated dry-wet cycling, which simulates moisture fluctuations that can occur in typical environments, has not been thoroughly investigated. This study evaluates the freeze-thaw resistance of blast furnace slag cement with different blast-furnace slag replacement ratios following repeated dry-wet exposure. The influence of entrained air, introduced via an air-entraining agent, was also examined. Freeze-thaw resistance was assessed using the RILEM CIF method, and microstructural characteristics were analyzed via mercury intrusion porosimetry. Results showed that, even though capillary pores became coarser with AE addition, the presence of adequate entrained air mitigated frost damage. In specimens without AE, increasing blast-furnace slag content improved resistance by reducing the prevalence of capillary voids formed during dry-wet cycling. These findings suggest that the microstructural changes induced by blast-furnace slag and AE agents play a crucial role in enhancing the frost durability of blast furnace slag cement under cyclic environmental stress.

This study explores the relationship between the physical properties of CO₂-absorbed CaCO₃ and the strength of BFS cement mortar. Four CaCO₃ powders with different specific surface areas and particle sizes were synthesized from industrial by-products. These CaCO₃ powders were used to partially replace BFS cement in mortar. Compressive strength was evaluated, and pore structure was characterized using mercury intrusion porosimetry (MIP). Paste samples were further analyzed to determine hydration degree by thermogravimetric analysis (TG), while early hydration behavior was investigated through isothermal calorimetry and X-ray diffraction (XRD). Although the average particle size, particle size distribution, and specific surface area of CaCO₃ from four different sources varied, the results suggest that CaCO₃ with a higher specific surface area can promote the reactivity of BFS, refine the pore structure, and improve compressive strength, while coarser particles are conducive to the formation of carboaluminate, thus contributing to long-term strength improvement. These findings provide guidance for optimizing CaCO₃ utilization in low-clinker cements and demonstrate the potential of synthetic CaCO₃ derived from industrial waste to enable carbon-negative cementitious materials.

Reinforced concrete structures in marine environments face rapid deterioration due to chloride-induced corrosion. This paper explores a bi-directional electromigration (BIEM) repair method using a cement composite conductive mortar containing an imidazoline rust inhibitor (IMZ), which achieves rapid extraction of chloride ions (Cl⁻) and sustained enrichment of IMZ in the vicinity of the steel. The findings reveal that the applied current density must be strategically selected based on the repair objective. A high current density of 5 A/m² was highly effective for the rapid electromigration and extraction of chloride ions (Cl⁻), capitalizing on the strong electrochemical driving force. In contrast, for the sustained migration and enrichment of the larger IMZ molecules at the steel surface, a prolonged application of a lower current density (3 A/m² for 28 days) proved far more effective, achieving a critical concentration of 0.18 wt%. This is mainly due to a positive shift of the corrosion potential by +600 mV and a 16-fold increase in polarization resistance after 28 days of continuous energization at 3 A/m². The IMZ/ Cl⁻ concentration ratio (R/C) evaluation index was established to assess the repair effect of corroded concrete and the degree of corrosion relief of steel reinforcement, when R/C > 1 indicates that the passivation. This approach provides a practical and effective framework for restoring durability in chloride-damaged marine concrete structures.

The environmentally friendly coal gangue planting concrete (CGPC) was prepared by leveraging the porous structure, nutrient reserves, potential reactivity, and solid waste characteristics of coal gangue. This provides an effective approach to comprehensively enhance the resource utilization of coal gangue solid waste and promotes ecological environmental governance. CGPC was prepared using activated coal gangue powder (ACGP) as a supplementary cementitious material and coal gangue as the aggregate. The influence of ACGP on the physical and mechanical property of CGPC was studied. Meanwhile, the influence of coal gangue powder as part of the guest soil on the planting property of CGPC was also studied. The results showed that low-content ACGP can fill the micropores in CGPC by micro-aggregate and pozzolanic effects, optimizing the structure of the interfacial transition zone between aggregate and paste, and significantly improves its mechanical property and frost resistance. The secondary hydration reaction of ACGP consumes a considerable amount of Ca(OH)₂, significantly reducing the alkalinity of CGPC and forming a more suitable environment for plant growth. Incorporation of 20% to 40% coal gangue powder into the guest soil effectively improves the growth status of the three plant species, especially Elymus dahuricus exhibits the most significant improvement.