Durability of Recycled Concrete Under the Coupling of Carbonation, Dry-wet and Freeze-thaw

To solve the problem of insufficient research on durability of recycled concrete under complex environmental conditions, the durability tests on five types of recycled concrete under the coupling of carbonation, dry-wet and freeze-thaw cycles were carried out. The dynamic elastic modulus, chloride ion migration coefficient, carbonation depth and micro-pore characteristics were measured, and the pore tortuosity was employed for analysis. Results show that carbonation and dry-wet alternating can significantly promote the freeze-thaw degradation of recycled concrete. The cumulative carbonation for 42 days and dry-wet for 42 times can increase the freeze-thaw damage of recycled concrete by 21.9%-26.9%, and decrease the chloride ion permeation resistance by 45.05%-96.18%. Compared with single carbonation for 42 days, the carbonation depth of recycled concrete can be increased 1.6-3.5 times by alternating 42 dry-wet cycles and 300 freeze-thaw cycles. In addition, carbonation and dry-wet increase the pore tortuosity, while freeze-thaw and the coupling of three environmental factors decrease. Moreover, the pore tortuosity significantly correlates with chloride ion migration coefficient and relative dynamic elastic modulus, which indicates that it can be used as an indicator of the durability of recycled concrete.