SELF-COMPACTING CONCRETE WITH FLY ASH AND CALCIUM CARBIDE WASTE: BINDER CHEMISTRY, WORKABILITY, AND STRENGTH

The incorporation of industrial by-products into cementitious materials can reduce Portland cement consumption and improve resource efficiency. This study investigated fly ash (FA) and calcium carbide waste (CCW) as partial replacements for Portland cement (PC) in self-compacting concrete (SCC). Eleven mixtures were produced, comprising a control and two replacement series with 5–25% FA or CCW. X-ray fluorescence (XRF), fresh-state properties (slump flow and L-box ratio), compressive strength at 14, 28 and 56 days, and tensile strength at 28 and 56 days were evaluated.XRF analysis showed that FA contained 59.04% SiO₂, 34.08% Al₂O₃ and 95.12% combined SiO₂ + Al₂O₃ + Fe₂O₃, indicating substantial pozzolanic potential, whereas CCW contained 64.00% CaO but only 3.36% combined reactive oxides. Increasing FA replacement improved fresh-state performance, with slump flow increasing from 690 to 770 mm and L-box ratio from 0.92 to 1.00 between 5 and 25% replacement. Conversely, CCW reduced slump flow from 680 to 640 mm and L-box ratio from 0.90 to 0.80. Replacement mixtures exhibited delayed early-age strength development but substantial later-age recovery, particularly with FA. At 56 days, PC–FA5 and PC–FA10 achieved 44.0 MPa compressive strength compared with 40.0 MPa for the control. The highest tensile strength was 8.54 MPa at 15% FA, while 25% CCW achieved 7.73 MPa at 56 days. Overall, FA provided the best balance of workability and later-age strength, whereas CCW exhibited poorer fresh-state behaviour at higher replacement levels.