Experimental Study On Strength Of Air-entrained Concrete Under Multiaxial Loads After Freeze-thaw Cycles

Freeze-thaw resistance is used as a key to measure the durability of concrete. Presently, most experimental and theoretical studies are focused on the relative dynamic modulus of elasticity, weight loss and the strength under uniaxial stress conditions of concrete after freeze-thaw cycles. While most concrete structures are generally working under multiaxial stress states. So, based on the project of National Nature Science Foundation named "multiaxial strength and failure criterion of concrete in freeze-thaw environments" (50479059), the experimental study and theoretical analysis on the uniaxial strength, multiaxial deformation and strength of air-entrained concrete and plain concrete are performed. Main contents in this paper are listed as follows:(1) The change of surface of air-entrained concrete and plain concrete specimens after different cycles of freeze-thaw were observed and analyzed, and the result of microcosmic configuration of plain concrete and air-entrained concrete was tested by electron microscope.(2) The dynamic modulus of elasticity, weight loss, compressive strength, tensile strength, flexural strength, cleavage strength and the ultrasonic velocity of plain concrete specimens with different water-cement ratio after freeze-thaw cycles were measured. The influence of freeze-thaw cycles on the mechanical property was discussed. The formulas to describe the relationship between the strength and freeze-thaw cycles were given. The stress-strain curves of plain concrete under uniaxial compression and uniaxial tension after different cycles of freeze-thaw were given.(3) The cubic compressive strength, compressive strength of air-entrained concrete specimens with different design compressive strength after freeze-thaw cycles were measured. The influence of freeze-thaw cycles on the mechanical property was discussed. At last, the tensile strength, cleavage strength, the dynamic modulus of elasticity, weight loss and the ultrasonic velocity of C30 air-entrained concrete were measured.(4) The experimental study of plain concrete under biaxial compression after freeze-thaw cycles was carried out. The failure envelope of plain concrete under biaxial compression in principal stress space was given. The influences of freeze-thaw cycles and stress ratio on the ultimate compressive strength and strain at the peak stress were analyzed. In addition, the failure criterion with consideration of the influence of freeze-thaw cycles and stress ratio was proposed. The stress-strain curves of plain concrete under biaxial compression after different...