Mechanical and self-sensing characteristics of cementitious composites incorporating heavy oil fuel ash

Self-sensing cementitious composites enable structures to monitor their condition continuously by tracking changes in their electrical conductivity (or resistivity) in response to stress, cracking, and damage. Heavy oil fuel ash (HOFA), a vastly underutilized byproduct of heavy oil-fired power plants, poses disposal challenges but offers significant potential for reuse. This study explores the potential of water-treated HOFA to exhibit self-sensing behavior when used as a partial replacement for ordinary Portland cement at 0%, 2%, 4%, and 6% by mass. An experimental study was conducted to characterize the chemical, mechanical, and piezoresistive properties of the developed smart cementitious composites. Results indicate that water treatment is a useful pre-treatment step that mitigates the early-age retarding effects of HOFA and yields a 12–56% improvement in the early-age compressive strength of mortars. In terms of self-sensing performance, the 2% HOFA mixture exhibited the best response, achieving a stress sensitivity of 0.60%/MPa and a strain sensitivity of 133 under a 15 kN load, and 0.28%/MPa and 67, respectively, under a 30 kN load. The 4% HOFA mixture also demonstrated comparable sensitivity and repeatability, with the added benefit of higher waste utilization.