Effect of TiO₂ and fly ash on photocatalytic NO_x abatement of engineered cementitious composites

Titanium dioxide (TiO₂) nanoparticles have been incorporated in cementitious composites to achieve photocatalytic (PC) functions such as self-cleaning and air purifying functions. This study experimentally investigates the effect of TiO₂ nanoparticles and fly ash on the nitrogen oxides (NO_x) abatement rate and efficiency of Engineered Cementitious Composites (ECC) that has retained strain-hardening properties and tensile ductility. Emphasis is placed on understanding the fundamental mechanisms through research on the microstructures and chemical environment of the composite material. A first-order chemical reaction model is applied to analyze the PC reaction rate and residual NO_x concentration. Test results indicate that the PC reaction rate and efficiency increase with the TiO₂ content from 0 to 5%, and the fly ash to cement ratio from 0 to 2.2. Using the low-calcium fly ash further increases the PC reaction rate and efficiency. The microstructure change originated from different fly ash contents and types are closely related to PC efficiency changes. This study advances the fundamental knowledge for engineering the cementitious composites to achieve the optimal PC functions.