Benefits of TiO₂ photocatalyst on mechanical properties and nitrogen oxide removal of ultra-high-performance concrete

This study aims to develop a novel type of ultra-high-performance fiber-reinforced concrete (UHPFRC) with excellent mechanical properties and nitrogen oxide (NO_x) removal capability. To achieve this, an inert filler, silica flour, was replaced with titanium dioxide (TiO₂), which is known as a photocatalyst. The test results indicated that the average bond strength of a straight steel fiber embedded in ultra-high-performance concrete (UHPC) increased by replacing the silica flour with TiO₂ powder up to 75% in general. Approximately 53% and 63% higher bond strengths and pullout energies, respectively, were thus achieved at 50% replacement rate. The tensile properties of UHPFRC were improved by TiO₂, and its tensile strength slightly increased, while the strain capacity and g-value substantially increased. The energy absorbing capacity increased by as much as 78% due to the addition of TiO₂ powder. Furthermore, the plain sample exhibited almost zero NO_x removal efficiency, but increased with the replacement ratio of TiO₂ powder up to 75%. The best NO_x removal capability in the UHPC sample containing 75% TiO₂ powder was thus 7.7 times higher than that of the plain sample.