Effect of curing regime on the performance and material efficiency of ultra-high performance concrete with sugarcane bagasse ash as filler

This study systematically investigates the effects of sugarcane bagasse ash (SCBA, replacement ratios from 0% to 80%) as a substitute for quartz powder (QP) as a filler on the properties of Ultra-High Performance Concrete (UHPC) under various curing regimes, including standard curing (SC), steam curing (SE), hot water curing (HC), and autoclave curing (AC). The application of thermal curing (SE, HC, AC) was found to significantly improve the early-age strength and chloride resistance. Moreover, increasing the SCBA content synergistically enhanced these beneficial effects. At an 80% SCBA replacement ratio, the 90-day flexural strength increased by 14.0%, 19.2%, and 24.8% for SE, HC, and AC, respectively, compared to SC, while the compressive strength increased by 6.6%, 10.5%, and 12.0%, respectively. Rapid chloride migration (RCM) results demonstrated that thermal curing markedly improved the early-age resistance to chloride penetration. Compared to the SC group, the chloride diffusion coefficients of the SE, HC, and AC groups at 3 days were reduced by 61.0%, 66.8%, and 73.0%, respectively. However, the extent of these reductions tended to moderate with extended curing age. Microstructural analyses (XRD, TG, MIP) indicated that thermal curing effectively activated the pozzolanic reactivity of SCBA, promoting the consumption of Ca(OH)₂, reducing total porosity, and refining the pore structure. Notably, after 28 days of SC, UHPC with 60% SCBA achieved mechanical and durability properties comparable to those of SE-cured specimens without SCBA. Based on XRD, TG, and internal relative humidity (RH) results, the performance gain is attributable to the pozzolanic activity and internal curing effect of SCBA. Material efficiency analysis identified the 80% SCBA mixture under SC as the optimal solution, demonstrating that SCBA enables the production of high-performance UHPC under low-energy conditions without the use of QP or thermal treatment.