This study investigates the improvement in the resistance of liquefaction of clean sand improved with coal-burning fly ash (CBFA) during curing. Tests using cyclic triaxial were conducted on specimens set at 50% relative density, mixed with 10% CBFA by dry weight, and cured for 0, 7, 14, 21, and 28 days under controlled humidity and temperature. Tests were conducted under isotropic confining pressures (CP) of 50, 100, and 200 kPa. The findings demonstrate that both cyclic shear stress (CSS) and liquefaction resistance ( \(\:{\mathbf{R}}_{\mathbf{L}}\) ) were markedly increased by the addition of curing time. The most substantial gains occur during the first 7–14 days of curing, attributed to ongoing pozzolanic reactions that bind soil particles and diminish strain accumulation. At 28 days, \(\:{\mathbf{R}}_{\mathbf{L}}\) and CSS increased by more than 100% compared with untreated sand, depending on CP, showing stress level dependency. The rate of strength development was more pronounced at higher CP, indicating a synergistic interaction between the mechanical confinement and chemical stabilization. These findings demonstrate that CBFA, an underutilized byproduct of coal combustion, has the potential to be a long-lasting and efficient stabilizer for liquefaction-prone sands, with optimal performance achieved after 21–28 days of curing. This study provides practical guidance for implementing CBFA-based ground improvement in seismic regions while promoting the beneficial reuse of industrial waste.
