Effects of curing conditions with different temperature and humidity on damage evolution of concrete during freeze-thaw cycling

To clarify the relationship between the curing conditions (temperature and humidity) of concrete and its frost resistance, several concretes with different water-binder (w/b) ratios and curing conditions were investigated by observing their microstructural damage in a freeze-thaw (F-T) environment using nuclear magnetic resonance (NMR). The results reveal that the curing temperature and humidity significantly influence the pore distribution and porous quality of concrete. With the decrease of the curing temperature and humidity and the increase of the w/b ratio, the proportion of macropores (0.05 mu m < r < 1 mu m) and microcracks (r >= 1 mu m) significantly increases. Compared with standard curing, the proportion of macropores and microcracks in concrete under the curing conditions of 10 degrees C-RH70% and 3 degrees C-RH50% increased by 16.21% and 26.71% respectively, while the frost resistance of concrete decreased. With the increase of the F-T cycles, the proportion of macropores and microcracks in concrete increased, the proportion of micropores (r < 0.01 mu m) and mesopores (0.01 mu m < r < 0.05 mu m) decreased, and the T-2 spectrum curve gradually moved to the right. Notably, the above-mentioned microstructure changes are reflected in the relative dynamic elastic modulus (RDEM). The total ratio of mesopores to macropores significantly influences the damage degree of concrete. Compared with the increase of the w/b ratio, the lack of curing temperature and humidity have greater influence on the frost resistance of concrete. The RDEM of concrete decreases with the increase of the F-T cycles, which is consistent with the change of the microcrack proportion.