The primary objective of this study is to investigate the effects of cylinder size (150 by 300 mm and 100 by 200 mm) on empirical equations that relate static elastic moduli and compressive strength and static and dynamic elastic moduli of concrete. For the purposes, two sets of one hundred and twenty concrete cylinders, 150 by 300 mm and 100 by 200 mm, were prepared from three different mixtures with target compressive strengths of 30, 35, and 40 MPa. Static and dynamic tests were performed at 4, 7, 14, and 28 days to evaluate compressive strength and static and dynamic moduli of cylinders. The effects of the two different cylinder sizes were investigated through experiments in this study and database collected from the literature. For normal strength concrete (≤40 MPa), the two different cylinder sizes do not result in significant differences in test results including experimental variability, compressive strength, and static and dynamic elastic moduli. However, it was observed that the size effect became substantial in high strength concrete greater than 40 MPa. Therefore, special care is still needed to compare the static and dynamic properties of high strength concrete from the two different cylinder sizes.

The present study intended to find a way to use TiO₂, one of the most widely used photocatalysts, as a construction material. To that end, nano-SiO₂/Al₂O₃-TiO₂ powder (NTCP) was synthesized by coating SiO₂ and Al₂O₃ support materials with TiO₂. The NTCP was anatase phase spherical particles, specific surface areas were 319 m²/g and 267 m²/g for the SiO₂-TiO₂ powder and Al₂O₃-TiO₂ powder. UV absorption test results showed the developed NTCP had a light absorption peak at wavelengths of 380 nm or below, and its absorbance was much larger than that of commercial TiO₂. The NTCP formed smaller pores on the surface than commercial TiO₂. As a result, the flow of the mortar decreased as the adsorption strength increased and combined a large number of water molecules. In addition, the Pozzolanic reaction by SiO₂ and Al₂O₃ used as support materials produced many calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H). This has shown an increased strength of mortar mixed with the NTCP by promoting a nucleation effect and reducing the filling effect and the number of harmful holes in the mortar.

The goal of this study was to improve the water purification performance of secondary concrete products that can be used in rivers and streams. To this end, mortar and porous concrete were produced by adding both de-nitrifying phosphate accumulating organisms ((D)PAOs) and zeolite, and their mechanical properties and water purification performance were analyzed. The compression strength test results showed that the strength was the highest when the mixing ratios of (D)PAOs and zeolite were set to 10% and 5%, respectively. For better contaminant adsorption, however, the optimal mixing ratio of zeolite was determined to be 10%. When the mixing ratio of (D)PAOs was set to 10%, the concentrations of biochemical oxygen demand (BOD) and chemical oxygen demand (COD) decreased by 57.9% and 89.9%, respectively, after seven days of immersion when compared to the initial concentrations. When compared to plain porous concrete, the total nitrogen (T-N) and total phosphorus (T-P) removal ratios of the develop concrete were 11.0% and 17.8% higher, respectively. When the mixing ratios of (D)PAOs and zeolite were set to 10% for both, the T-N and T-P removal ratios were determined to be 86.3% and 88.1%, respectively, while the BOD and COD concentrations were 2.668 mg/L and 16.915 mg/L, respectively. In simpler terms, the water purification performance was up to 17% higher in the concrete mixed with both 10% (D)PAOs and 10% zeolite than in the concrete mixed with 10% (D)PAOs only. Overall, the optimal mixing ratios of (D)PAOs and zeolite to maximize the water purification effect of secondary concrete products while maintaining their strengths equivalent to or higher than those of their corresponding plain concrete products are considered to be 10% for both.

This study investigated the feasibility of utilizing chloride bypass dust (CBPD) and its washed residue (WR), which are byproducts of the cement industry, as controlled low-strength materials (CLSM). The fundamental mix design characteristics were examined by replacing ordinary Portland cement (OPC) and slag cement (SC) with CBPD and WR at substitution ratios of 25%, 50%, and 75%,respectively. The effects on water-to-cement ratio (W/C), flowability, and compressive strength were analyzed. As the replacement level increased from 25% to 75%, both CBPD and WR mixtures exhibited reduced flowability and compressive strength. Notably, WR required a higher W/C than CBPD to maintain equivalent workability, which was attributed to the pronounced early hydration activity of portlandite, a primary mineral in WR. Compressive strength measurements •