The use of titanium dioxide in concrete block pavements is a promising approach to reduce air pollution in the roadside. When TiO₂ is used as an additive of cement concrete or mortar, it is not dispersed uniformly due to agglomeration between particles causing the degradation of photocatalytic reaction. To improve the photocatalytic performance of TiO₂, the Nano SiO₂-TiO₂ (NST) has been developed by coating TiO₂ with SiO₂ as a support using the sol-gel method. The environmental performance of concrete blocks incorporating NST as an additive was evaluated using both laboratory and full-scale chamber experiments. It was observed from laboratory environment chamber testing that the NO reduction efficiency of concrete blocks with 4% NST ranged from 16.5 to 59.1%, depending on the UV intensity. Results of the full-scale chamber test on NST concrete blocks indicated that the NO and SO₂ reduction efficiencies were 22.3% and 14.4% at a 564 W/m² of solar radiation, respectively. It was found that the increase in UV intensity and solar radiation had a positive effect on decreasing NO and SO₂ concentration. In the future, the NST will be applied at in-service photocatalytic block pavements to validate the environmental performance in field conditions.

This paper presents an investigation of the characterization of cement mortar containing phase change materials (PCMs) in order to control the development of hydration heat. The study examined microstructural characteristics and properties of cement mortar with PCMs such as flow, compressive strength, and flexural strength. This research involved two types of PCM and up to 15% cement added to cement mortar mixtures. The two types of PCM used in this study are PCM with barium (PCM-Ba) and PCM with strontium (PCM-Sr). The experimental results indicate that both the incremental temperature rise and the maximum temperature release time of PCM up to 5% addition are delayed. Both PCM-Ba and PCM-Sr are effective in reducing the development of hydration heat. The microstructural analysis results show that the crystalloid content of cement mortar without PCMs is about 3% more from cement mortar with PCMs, regardless of the type of PCMs used, and that no significant difference is evident in the formation of crystals between cement mortar with and without PCMs.

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.

Nitrogen oxide (NOx), emitted at the highest rate among automobile exhaust gases, is the main cause of air pollution, and various construction technologies are being developed to reduce NOx emissions. In this study, the NOx reduction effect of surface treatment technology for road pavements, and the effect of the photocatalytic reaction on asphalt pavements, were evaluated using a photocatalyst. Three types of titanium dioxide (TiO₂) were used as photocatalysts, and an asphalt rejuvenator used to recover aged asphalt was applied as a surface treatment agent. To evaluate the NOx reduction effect, a test device capable of testing large-sized specimens was manufactured and compared with the ISO method, which only allowed the testing of small specimens. In addition, the effect of TiO₂ and the asphalt rejuvenator on the asphalt mixture was analyzed through chemical analysis. The test results of the newly manufactured mixed-tank photo reactor showed the same trend as the ISO test results concerning the evaluation of its NOx removal performance. As a result of the performance evaluation of the surface treatment using TiO₂, the NO removal rate was up to 7.83% when Anatase-type TiO₂ with excellent light efficiency was applied. In addition, when the rejuvenator was used, the oxidation of asphalt, caused by the photoreaction of TiO₂, was reduced.

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.

A significant amount of stone sludge is generated as a by-product during the production of crushed stone aggregate, and most of it is disposed of in landfill as waste. In order to recycle this stone sludge, this study evaluated a controlled low-strength material (CLSM) using ultra-rapid-hardening cement and stone sludge for application as backfill and subbase material for road excavation and restoration work. In addition, considering the limited construction time of excavation and restoration work in urban areas, backfill and subbase materials must simultaneously satisfy conditions of fluidity, workability, quick curing time, and certain levels of strength. Therefore, in this study, CLSM was manufactured according to various mixing ratios and flow, slump, and compressive strength tests with age were evaluated. Additionally, the change trend in the microstructure of the CLSM with age was analyzed. Through indoor experiments, the optimal mixing ratios for backfill and subbase CLSM were determined, and field applicability and performance of field samples were evaluated through small-scale field construction. It was concluded that CLSM, which contains a large amount of stone sludge, can be sufficiently applied as a backfill and subbase material for excavation and restoration work if appropriate admixtures are adjusted according to the weather conditions at sites.