Short-Term Performance of HVFA-SCC Incorporating Bottom Ash, Sodium Hydroxide, and Calcium Carbonate: Physical and Mechanical Properties

The utilization of HVFA in Indonesia's infrastructure projects is still limited, ranging from 15% to 45%. Meanwhile, the increase in infrastructure development pushes the demand for cement and concrete production higher. This problem is concerning because Portland Cement (PC) significantly contributes to carbon dioxide emissions. This study analyzes the short-term performance of HVFA-SCC concrete for up to 28 days, focusing on workability, setting time, compressive strength, and flexural strength of unreinforced beams. The aim is to examine the effects of 60% and 70% FA substitution for PC, 20% Bottom Ash (BA) substitution for natural fine aggregate (NFA), 0.05 Molar Sodium Hydroxide (NaOH), and 5% Calcium Carbonate (CaCO₃). There are six mixed variations: HVFA-SCC + 60A, HVFA-SCC + 60A + BA, HVFA-SCC + 70A, HVFA-SCC + 70A + BA, Control-60A, and Control-70A. The results show that HVFA-SCC concrete has lower flowability and setting times than the controls. Using 70% FA, 20% BA, 0.05 M NaOH, and 5% CaCO₃ reduces the flow diameter by 1.17% for HVFA-SCC + 70A and 1.48% for HVFA-SCC + 70A + BA compared to HVFA-SC + -60A and HVFA-SCC + 60A + BA. HVFA-SCC + 60A and HVFA-SCC + 60A + BA, without NaOH and CaCO₃, have the most extended setting times: 405 and 313 min for the initial setting and 549 and 421 min for the final setting, respectively. After 28 days, HVFA-SCC concrete reached a maximum compressive strength of 48.559 MPa, below the 50 MPa target. In contrast, Control-60A and Control-70A exceeded the target with 51.019 MPa and 50.277 MPa, respectively. All HVFA-SCC beams had lower flexural capacity than the controls but met acceptance criteria, with HVFA-SCC + 60A showing the highest capacity at 5.78 MPa.