Influence of damage degree on the degradation of concrete under freezing-thawing cycles

The existed studies about the freezing-thawing degradation of concrete mainly focused on non-damaged concrete. This may overestimate the service life of concrete structures. In this paper, the influence of damage degree on the degradation of concrete under freezing-thawing cycles was systematically investigated. The concrete specimens with three different damage degrees (0, 10%, and 20%) of D-0, D-1, and D-2 were prepared. After many freezing-thawing cycles, the mass loss, relative dynamic modulus of elasticity were measured and uniaxial compression tests were conducted. Test results show that the mass of D-0 continuously increases with the freezing-thawing cycles before 32, but the mass of D-1 and D-2 specimens show a negative increase after 16 cycles. The relative dynamic elastic modulus of D-1, D-2, and D-3 showed a decreasing trend. The degradation rate of compressive strength is close to the no-damage concrete when the damage degree is less than 0.1. However, when the damage degree reaches 0.2, the degradation rate of strength accelerates remarkably. The elastic modulus of D-0, D-1, and D-2 specimens decreases linearly with the increase of freezing-thawing cycles. The peak strain varies of D-0 specimen change very little before 32 freezing-thawing cycles. For D-1 and D-2 specimens, the peak strain increases linearly with the increase of freezing-thawing cycles. Finally, the degradation mechanism of concrete with initial damage under the action of freezing-thawing cycles are discussed. (C) 2020 Elsevier Ltd. All rights reserved.