In this study, the flexural behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) is examined as a function of fiber length and volume fraction. Straight steel fiber with three different lengths (l_f) of 13, 19.5, and 30 mm and four different volume fractions (v_f) of 0.5%, 1.0%, 1.5%, and 2.0% are considered. Test results show that post-cracking flexural properties of UHPFRC, such as flexural strength, deflection capacity, toughness, and cracking behavior, improve with increasing fiber length and volume fraction, while first-cracking properties are not significantly influenced by fiber length and volume fraction. A 0.5 vol % reduction of steel fiber content relative to commercial UHPFRC can be achieved without deterioration of flexural performance by replacing short fibers (l_f of 13 mm) with longer fibers (l_f of 19.5 mm and 30 mm).

This study aims to examine the mechanical, shrinkage and chemical properties of photocatalytic cementitious materials containing synthetic fibers and a shrinkage-reducing admixture (SRA). Two types of titanium dioxide (TiO₂) powders and white Portland cement were considered along with ordinary Portland cement (OPC) as a control. Two types of synthetic fibers, i.e., glass and polyethylene (PE), and an SRA with contents varying from 0% to 3% were also considered. Using the TiO₂ powders and the white Portland cement was effective in reducing the nitrogen oxides (NO_x) concentration in cement composites. The use of PE fibers was more effective than glass fibers in terms of the mechanical properties, i.e., the compressive strength and tensile performance. With the addition of TiO₂ powders and SRA or the replacement of OPC with white cement, the mechanical properties of the cement mortar generally deteriorated. The total shrinkage of the mortar could be reduced by incorporating the fibers at volume fractions greater than 1%, and the glass fiber was more effective than the PE fiber in this regard. The TiO₂ powders had no significant impact on the shrinkage reduction of the cement mortar, whereas the SRA and the white Portland cement effectively reduced shrinkage. The addition of 3% SRA decreased the total shrinkage by 43%, while the replacement of the OPC with white cement resulted in a 20% reduction in the shrinkage.

This study examined the effect of adding synthetic fibers, that is, polypropylene (PP) and nylon (Ny), on explosive spalling and residual tensile mechanical properties of high-performance fiber-reinforced cementitious composites (HPFRCCs). Three different matrix strengths (100 MPa, 140 MPa, and 180 MPa), four different volume contents of the synthetic fibers (0%, 0.2%, 0.4%, and 0.6%), and three different exposure time (1 h, 2 h, and 3 h) based on the Internatinoal Organization for Standardization (ISO) fire curve were adopted as variables for this experiment. The experimental results revealed that the addition of synthetic fibers improved the resistance to explosive spalling induced by high-temperature, especially when PP and Ny were mixed together. For a higher matrix strength, greater volume content of the synthetic fibers was required to prevent explosive spalling, and higher residual strengths were obtained after the fire tests. An increase in the volume fraction of the synthetic fibers clearly prevented explosive spalling but did not affect the residual tensile strength. In the case of a higher matrix strength, a reduction in the strength ratio was observed with increased exposure time.

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.