Mechanical Performance and Strength Prediction of Non-Steam-Curing UHPC Considering Coupled Temperature-Constituent Effects

Non-steam-curing ultra-high-performance concrete (UHPC) is a promising material for in situ bridge deck rehabilitation; however, its strength development under variable curing temperatures remains insufficiently understood. This study investigated the coupled effects of curing temperature and constituent dosage on the mechanical performance of non-steam-curing UHPC. Compressive and flexural strength tests were conducted on mixtures incorporating different dosages of silica fume, microspheres, and steel fibers. Based on the experimental results, two predictive models were developed to describe the time-dependent strength evolution of UHPC at the optimal mixture proportion and the later-age strength as a function of curing temperature and constituent dosage. The results showed that silica fume had a significant influence on early-age strength, but its effect was strongly dependent on curing temperature and age. At low curing temperatures, silica fume initially reduced early-age strength, whereas its contribution became positive with prolonged curing. When the microsphere dosage exceeded 55 kg/m3, early-age strength decreased with increasing microsphere content; however, this adverse effect gradually weakened and eventually became beneficial as curing temperature and curing age increased. Increasing the steel fiber dosage from 40 to 160 kg/m3 consistently improved both compressive and flexural strengths, whereas further increases produced only marginal additional enhancement. The proposed models captured the temperature-dependent strength development of non-steam-curing UHPC and provide a quantitative basis for mixture optimization and construction-stage strength prediction in bridge rehabilitation applications.