Concrete subjected to freeze-thaw cycles action at early-age will suffer serious physical damage, resulting in degradation of the concrete's performance. The subsequent curing conditions after early-age freeze-thaw cycles (E-FTCs) are critical to the development of the properties of frost-damaged concrete. Four test environments were set up for this study, based on different numbers of E-FTCs and subsequent curing conditions. The later-age resistance to freeze-thaw of concrete exposed to E-FTCs was evaluated by analysing the influence of precuring times and curing conditions. Results show that the earlier the FTCs occur, the worse the later-age freeze-thaw resistance is. In particular, for the frost-damaged concrete with a pre-curing time of 18 h, its freeze-thaw resistance is significantly worse than that of other concretes that have a longer pre-curing time. The increase in the number of E-FTCs exacerbates the damage to early-age concrete, which causes the reduced laterage freeze-thaw resistance. Subsequent water curing can significantly improve the freeze-thaw resistance of damaged concrete, while air curing is the least effective. Based on previous freeze-thaw damage models, prediction models for concrete exposed to E-FTCs were created by using the test data obtained in this study. The critical pre-curing strengths which can ensure that the damaged concrete has satisfactory frost resistance at laterage were thus obtained. For concrete structures expected to experience E-FTCs, adequate pre-curing strength and good re-curing conditions are essential.Abbreviations: DF, Durability factor; E-FTC, Early-age freeze-thaw cycle; FTC, Freeze-thaw cycle; MLR, Mass loss rate; RDME, Relative dynamic modulus of elasticity; 10-WC, Cured in water to age 28 d after 10 E-FTCs; 20-SC, Cured in standard curing room to age 28 d after 20 E-FTCs; 20-WC, Cured in water to age 28 d after 20 E-FTCs; 20-NC, Cured in natural air to age 28 d after 20 E-FTCs.

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Early-age frost damage to concrete used in winter construction or in cold environments negatively affects the development of the hydration process and the performance of the concrete, thereby reducing the service life of the building structure. Experimental research was carried out to investigate the compressive strength, resistance to chloride penetration and resistance to freeze-thaw of concrete specimens subjected to earlyage freeze-thaw cycles (E-FTCs). The effects that different pre-curing times of concrete and mineral admixtures have on the properties of early-age frostaffected concrete were also analyzed. Results show that the earlier the freeze-thaw cycles (FTCs), the poorer the later-age performance. Later-age water-curing cannot completely restore the damage that E-FTCs do to concrete. In the same conditions used in this study, the effects of E-FTCs on later-age mechanical and durability properties of ordinary Portland cement concrete (OPC) are small. The incorporation of fly ash significantly reduces the resistance to freeze-thaw of concrete during early-age and later-age. The presence of silica fumes has an adverse effect on the later-age resistance to freezethaw. In general, the recovery percentage of later-age durability indexes of concrete subjected to E-FTCs is lower than that of compressive strength. For concrete subjected to E-FTCs, it is more important to ensure the recovery of later-age durability.

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