Mechanical behavior and chloride penetration of high strength concrete under freeze-thaw attack

This paper proposes an experimental study to investigate the freeze-thaw (FT) effects on mechanical behavior and chloride diffusion in high strength concrete. Sets of high strength concrete cubes are cyclically frozen in range from + 18 degrees C to - 20 degrees C. The mechanical property and the chloride penetration tests are performed on the specimens after 0, 5, 10 ... 95, and 100 FT cycles. FT effects on surface scaling damage, compressive strength, elastic modulus, stress-strain relationship and chloride resistance of high strength concrete are clarified. Also, a simple model is discussed and verified to predict the chloride concentration of high strength concrete attacked by FT cycles. Results show that the behavior of high strength concrete depends on the number of FT cycles. Visible damages appear in concrete after about 40 FT cycles. Before 25-60 FT cycles, no significant difference exists in FT-caused weight loss between normal strength concrete and high strength concrete. Beyond this, the FT-caused weight loss in normal strength concrete becomes faster than that in high strength concrete. FT damage decreases the compressive strength, the elastic modulus and the chloride resistance of concrete, but increases its ductility. In the present test, the compressive strength and elastic modulus decrease about 32% and 24% after 100 FT cycles, respectively. The surface chloride concentration and chloride diffusion coefficient increase to about twice of the control values.