This study investigates the carbonation degree of reclaimed water (RW) and its potential use as mixing water for cementitious materials under controlled laboratory conditions using a simplified CO₂ injection method. To reproduce the chemical environment of actual RW, a synthetic reclaimed water (SRW) system with a cement-to-sand ratio of 8:2 was prepared and used throughout the evaluation. Thermogravimetric analysis revealed that the cementitious solids suspended in SRW exhibit high reactivity with CO₂, achieving a net CO₂ uptake of 16.8%, equivalent to 8.31 g of CO₂ sequestered per kilogram of RW. The use of untreated RW as mixing water slightly reduced flowability and increased superplasticizer demand compared with distilled water, whereas carbonation treatment of RW improved workability and mitigated the rapid initial setting typically observed with untreated RW. Notably, replacing 3% of the cement with carbonated RW solids did not cause any reduction in compressive strength, indicating that the carbonated solids can be incorporated without compromising mechanical performance. These results confirm that the CaCO₃ formed during RW carbonation remains stably retained within mortar and concrete, demonstrating the feasibility of using carbonated RW as a dual-function material—serving both as mixing water and as a medium for CO₂ sequestration.

In this study, cementless concrete was produced by completely replacing cement with ground granulated blast furnace slag (GGBFS) and using calcium hydroxide (CH) as the alkali activator. The effects of silica fume (SF) substitution (0%, 10%, and 20%) and curing conditions (ambient, high-temperature steam, and high-temperature water) on the fundamental properties of cementless concrete were examined. Higher SF content reduced slump flow but maintained adequate filling ability. The lower pH of CH delayed setting, particularly at higher SF substitution levels. Under high-temperature curing, pozzolanic reactions improved strength development, resulting in compressive and flexural strengths of 106.1 MPa and 28.3 MPa, respectively, at 20% SF substitution with high-temperature steam curing. The developed cementless concrete is expected to serve as a high-strength, low-carbon structural member for use in precast and modular concrete industries that use high-temperature curing processes.

Pilot-scale validation of controlled CO₂ curing for reinforced concrete members remains limited. This study developed a 2400 L high-temperature CO₂ curing chamber integrating control of temperature, relative humidity (RH), CO₂ concentration, and pressure with real-time monitoring and automated CO₂ regulation. Its applicability was evaluated using commercial concrete bricks and a reinforced concrete slab through mass monitoring, compressive strength testing, phenolphthalein-based carbonation assessment, thermogravimetric analysis (TGA), flexural testing, and carbonation depth measurement. Real-time mass monitoring showed a net mass gain of 50.7 g after 1 h, corresponding to 2.8% of the initial mass. The CO₂-cured bricks achieved a compressive strength of 9.77 MPa, with a calculated CO₂ uptake of 5.72% based on TGA. The CO₂-cured slab exhibited a compressive strength of 41.9 MPa, comparable flexural load capacity to the steam-cured slab, and a higher ductility index of 6.86. Carbonation remained within the concrete cover without reaching the reinforcement. Within the scope of the investigated materials and curing conditions, these results demonstrate the pilot-scale feasibility of controlled CO₂ curing for commercial concrete products and reinforced concrete members and provide a basis for further member-scale validation and process optimization.