Experimental study on cyclic tensile behaviour of air-entrained concrete after frost damage

To investigate fatigue tensile behaviour of air-entrained concrete after the freeze–thaw damage, fatigue tensile tests with four different loading paths were conducted on air-entrained concrete after 0, 100, 200 and 400 freeze–thaw cycles. The four different loading paths contained the monotonic (M) test where the envelope stress–strain curve was obtained, the cycles with constant strain increment (CSI) test where the variation of elastic modulus on the whole stress–strain curve was studied, the cycles to variable maximum strain amplitude (VMS) test where the low-cycle fatigue behaviour at different strain levels was analysed and the cycles with CMS’ test, which was designed to analyse the post-peak behaviour of the specimens. Experimental results indicated that the properties of the air-entrained concrete basically remained unchanged under 200 freeze–thaw cycles, including the mass loss rate, tensile strength, elastic modulus and the dissipated energy per unit volume. While the freeze–thaw cycles increased over the critical value, the energy resulted from the cyclic load was not released from the materials and accumulated inside the materials fast. Energy accumulation directly led to the deterioration of the air-entrained concrete. To observe the pore structure of the air-entrained concrete, the scanning electron microscope test (SEM) was also adopted in this paper.