Surface and microstructural properties of photocatalytic cements for pavement applications

Thin concrete inlays incorporating flowable fibrous concrete (FFC) mix designs as well as titanium dioxide (TiO2)-containing photocatalytic cements are a promising pavement preservation solution. These multi-functional inlays offer enhanced constructability and structural properties while also benefiting the environment by reacting with harmful nitrogen oxides (NOx) and removing them from the near-road environment. Photocatalytic FFC mixes were prepared in the laboratory to verify feasibility of field application and to characterize how mixture and microstructural properties and environmental factors affect photocatalytic performance. Testing of fresh and hardened concrete confirmed the ease of application of photocatalytic FFC and its benefits to the pavement's structural properties, particularly to residual strength ratio and fracture toughness. Laboratory photoreactor testing of mortar samples established that photocatalytic FFC is an effective tool to mitigate NOx pollution in the urban environment. Carbonation of the sample surface was shown to have the potential to significantly reduce NOx removal ability, but this effect could be curtailed by replacing some of the cement with fly ash or increasing TiO2 content by mass of cement. Spectrophotometer testing showed that reflectance of the mortar samples also factored into photocatalytic performance. More reflective specimens demonstrated greater NOx removal ability, which was most apparent when comparing the performance of white cement specimens to gray cement specimens. Finally, analysis of cement paste specimens using scanning electron microscopy (SEM) and related techniques suggested the importance of porosity to photocatalytic ability. These findings will be useful in helping design and optimize photocatalytic concrete mix designs for applications in pavements and other structures. Based on the results of the mixes and materials tested, a white cement photocatalytic concrete with 15% fly ash replacement would offer the most optimal balance between high photocatalytic efficiency and resilience to carbonation