Effects of high-low temperature cycles on the performance of coral aggregate concrete based on field specimens and laboratory accelerated tests

In the high-temperature marine environment, breakwaters frequently suffer from high-low temperature cycles, which inevitably damages the performance of coral aggregate concrete (CAC). Based on field specimens and laboratory tests, in this research, the evolution of macroscopic and microscopic properties, as well as the crack density of CAC under high-low temperatures action were investigated, then the damage mechanism of CAC was revealed. The experimental results showed that the compressive strength of the specimens derived from the outside and top surface of on-site breakwater ranged from 24.07 to 55.48 MPa and from 26.26 to 43.41 MPa, respectively, and their splitting compressive strengths ranged from 1.29 to 4.65 MPa and from 1.68 to 4.49 MPa, respectively. In addition, fine cracks and swelling products can be found in the CAC. Under the indoor accelerated test of seawater cooling, the compressive strength of the indoor CAC developed in an increasing and then decreasing trend with the increase of the cycle period, whereas the splitting tensile strength kept developing in a decreasing trend, this was caused by the dual action of high-low temperatures cycles and sulfate erosion. Additionally, the interior of CAC also exhibited more calcium alumina, gypsum, and sodium sulfate crystal. Moreover, the addition of fly ash (FA), silica fume (SF), and polypropylene fiber (PF) can reduce the strength loss of CAC under high-low temperature cycles to some extent. The mathematical relationship between the relative dynamic elastic modulus of the CAC and the cycle period could be fitted by a quadratic polynomial (E-rd = a + bt + 0.5ct(2), R-2 greater than 0.99).