The aim of the research is to achieve the strength development performance of high-volume slag concrete or zero-cement concrete with 0.45 of W/B by incorporating of recycled aggregates as a cost-effective alkali activator. Based on the blast-furnace slag (BFS) based cement, like an alkali activated slag (AAS), recycled aggregates were replaced by natural aggregates and were used as an alkali activator for BFS. For compressive strength improvement in concrete, different replacement ratios of ordinary Portland cement ranged from zero to 50%, recycled fine aggregates (RFA) and recycled coarse aggregates (RCA) ranged from zero to 100% were varied. The test results indicated that recycled aggregates could be used as an alkali activator for BFS, and they were also able to help achieve about 90% of compressive strength of the concrete with natural aggregate depending on its optimum proportion with BFS.

The aim of this research is to provide a quantitative method for evaluating concrete segregation. Because of various conditions of concrete materials, mix proportions, and delivery, concrete can be segregated. The acquisition inspection executed in construction field for supplied ready-mixed concrete is an important quality control process for concrete. Among the inspections conducted at the project site, segregation of concrete mixture should be evaluated before placing the concrete mixture, currently a qualitative inspection on concrete segregation was conducted. For a normal concrete mixture with slumping behavior, shear slump or collapse slump often occur as an indication of segregation. The suggested evaluation index of segregation for normal concrete (EISN) was induced from the shape of the concrete slumping: relation between the maximum distance of flow and the minimum distance of flow. To evaluate the feasibility of EISN, two different concrete mixture conditions were tested. The recommended EISN parameter of segregation is 1.09 using the three grades of concrete quality. This new quantitative method of evaluating segregation of the concrete mixture is expected to contribute to a more efficient quality control in concrete construction.

Research on concrete durability during prolonged use has been ongoing due to concrete’s widespread use in construction. Freeze–thaw cycles exert a significant impact on concrete durability, especially in regions with harsh climates. While existing studies primarily focus on material aspects, research on the performance degradation of reinforced concrete (RC) structures is limited. This limitation is attributed to the inadequacy of current freeze–thaw testing standards for large structures like RC structures. Therefore, there is a need to propose freeze–thaw testing methods tailored for RC members. This study investigates the influence of air content and freeze–thaw cycles on the material and structural properties of RC beams, proposing a novel rapid freeze–thaw testing method for RC members. The study compares this new method (N test) with the conventional ASTM C666/C666M-15 rapid freeze–thaw testing procedure (A test), aiming to establish a correlation between the two experiments. Concrete mixtures with air content ranging from 0 to 9% underwent two types of freeze–thaw tests, followed by flexural testing of RC beams. The results were analyzed for air content, slump, compressive strength, mass loss, crack patterns, and failure modes, and they offer insights into the relationship between air entrainment, freeze–thaw resistance, and the structural behavior of RC under diverse environmental conditions.

Research on the long-term durability of concrete has continued due to its widespread application in construction. Freeze–thaw cycles significantly impact concrete durability, particularly in regions with harsh climates. While most studies focus on the material properties of concrete, limited research has addressed the performance degradation of reinforced concrete structures. This study investigates the freeze–thaw resistance of RC beams made with 35 MPa concrete, with particular emphasis on the influence of air content on flexural performance. RC beams were exposed to freeze–thaw cycles using the air freeze–thaw method and the ASTM C666/C666M-15 water freeze–thaw method. Their flexural behavior was evaluated through four-point bending tests. The results showed that low-air-content RC beams exhibited notable reductions in yield load and energy absorption capacity after freeze–thaw cycles, indicating decreased strength and ductility. Conversely, RC beams with appropriate or high air content exhibited minimal reductions, demonstrating superior freeze–thaw resistance. These findings underscore the importance of optimizing air content to enhance the durability of RC structures in harsh environmental conditions.

The aim of the research is to investigate thixotropy in high-fluidity normal-strength cement paste containing PVA and borax. Although high-fluidity concrete offers advantages such as reduced ease of placement and improved concrete quality, it also presents disadvantages, including increased formwork pressure and a higher risk of segregation. Thixotropy is the rheological property of securing the stability of fresh state cement-based materials, depending on the applied forces on them. Although many studies and techniques have suggested that clay can impart thixotropy to cement-based materials, the thixotropy imparted by clay is relatively weak, and recovery is slow. In this research, thixotropy was applied to cement-based materials using the cross-link between PVA and borax. Based on the tests conducted, the cross-link between PVA and borax remained effective within the cement-based materials, and thixotropic behavior was observed. Additionally, the setting time delay due to using borax was resolved by reduction slag. Finally, based on the optimal proportions of PVA, borax, and reduced slag for high-fluidity normal-strength cement paste with high thixotropy, the material was applied to simulate formwork gaps and evaluate its leakage-reducing performance. The high-fluidity cement mortar showed progressive performance in reducing formwork leakage, particularly with PVA and borax, due to its high thixotropy. Based on the research results, it is possible to impart thixotropic behavior to cement-based materials using PVA and borax, and to safely use high-fluidity cement-based materials.