Damage evolution and mechanism of concrete erosion at sulfate environment in underground mine

Some experiments were conducted to simulate the mechanical characteristics and deterioration of concrete under sulfate and wet-dry cycle environment. The parameters were tested and analyzed, including compressive strength,splitting tensile strength, bending strength, the variation of mass and ultrasonic velocity and stress-strain curves over attacked time. The damage development was evaluated by multi-index of attacked concrete based on dam- age mechanical theory. The relationship between the corrosion damage and stress-strain characteristics was analyzed. The damage model of corroded concrete was established considering the effects of the parameters such as corrosion time and strain on the damage evolution. According to the ESEM images and XRD results,the damage mechanism was obtained by analyzing the microstructures of concretes at different erosion periods. The research results show that:① Under the coupling action of sulphate attack and drying-wetting cycles, the parameters, including the compressive strength,splitting tensile strength,bending strength and ultrasonic velocity,increase first and then decrease with ero- sion time,and especially the splitting tensile strength and bending strength signature are more sensitive to damage and deteriorate more seriously. According to data regression,the corrosion damage evolution equations were developed. In the equations these performance indicators were regarded as damage variables. Linear functional relationship exists a- mong different damage factors. ② In the long term,with corrosion time the peak stress decreased while peak strain in- creased. Elastic modulus and deformation modulus also decreased. The damage caused by corrosion and the one caused by load were unified by means of mathematical model,which revealed the relationship between and among sulphate at- tack,load and damage to concrete in complex underground environments. ③ During the erosion time,the combined ex- pansions of ettringite,gypsum and the crystal of sodium sulfate decahydrate cause micro fractures. With the increase of corrosion time,the micro-cracks developed and their number increased.