Mechanical properties and compressive strength development of concrete under early-age low-temperature exposure with different binder compositions

This study quantified the effects of early-age low-temperature exposure and binder composition on the mechanical properties of concrete. Specimens prepared from concrete mixtures with W/B = 0.50 were exposed to −5 °C for 0, 3, or 12 h immediately after casting. They were then sealed-cured at 10 °C, while standard curing was used as the reference condition. Three binder systems were considered: B1 with OPC 100%, B2 with OPC 70% + GGBS 15% + FA 15%, and B3 with OPC 30% + GGBS 55% + FA 15%. Compressive strength, splitting tensile strength, modulus of elasticity, and stress–strain relationship were measured to evaluate strength- and stiffness-related responses under the imposed temperature history. The 28-day compressive strength decreased as the exposure duration increased. The reduction became greater as the replacement levels of GGBS and FA increased. Early-age strength development was also delayed, indicating higher exposure sensitivity in the blended systems. The stress–strain relationship retained the typical overall compressive form. However, both the initial slope and peak stress decreased as exposure duration increased. Most measured modulus values were lower than the ACI 318-14 reference at a comparable compressive strength level. The modulus coefficient also decreased under the low-temperature conditions. The normalized tensile-strength ratio also decreased with exposure duration. This result indicates that the tensile response was more sensitive to the imposed temperature history than would be inferred from compressive strength alone. An equivalent-age-based empirical model was developed by separating the contributions of subzero and positive-temperature histories. Within the calibrated range, the model reproduced the overall trend of age-dependent compressive-strength development.