Exploring the impact of titanium dioxide on the physical and mechanical properties of roller-compacted concrete pavement containing class F fly ash by response surface methodology

This study examines the effects of substituting ordinary Portland cement with 0%, 5%, and 10% of the additive titanium dioxide (TiO ₂ ) and incorporating class F fly ash (FFA) at levels of 0%, 30%, and 60% on the physical and mechanical properties of roller-compacted concrete (RCC) pavement using the soil compaction method. The response surface method (RSM) evaluated the compressive strength at 28 and 90 days of curing and the flexural and split tensile strengths and water absorption at 90 days. The findings from the laboratory tests revealed that TiO ₂ alone in the samples improved the compressive, flexural, and split tensile strengths while reducing porosity and water absorption. As the amount of TiO ₂ increased, the improvements also grew, with the most notable enhancement occurring at 10% TiO ₂ . On the other hand, FFA alone led to decreased strength and water absorption, with the most favorable results seen at a 30% FFA content. Increasing the FFA content up to 60% led to a further decrease in strength and increased water absorption. Combining FFA and TiO ₂ resulted in weakened strengths. Increasing TiO ₂ with a lower amount of FFA improved water absorption and porosity; however, this improvement lessened as the FFA content increased. The RSM analysis indicated that samples containing only 10% TiO ₂ and 11.53% FFA exhibited the highest strength and optimal water absorption after 90 days of curing. The scanning electron microscopy images indicated that the microstructure was denser with the use of TiO ₂ , and increasing the TiO ₂ content resulted in a microstructure that was even denser compared to the control sample. However, using FFA resulted in microcracks, and increasing the amount of FFA alone or with TiO ₂ led to more significant sample fragmentation.