Effect of freeze-thaw cycling on fatigue behaviour in concrete

Freeze-thaw damage is a deterioration mechanism caused when saturated concrete is exposed to temperature variations that cycle above and below its freezing point. The expansion of water in the concrete pore space due to freezing can lead to internal pressures that induce cracking, thus expediting the deterioration process through freeze-thaw cycles. The purpose of this investigation was is to evaluate the effect of freeze-thaw deterioration on the tensile fatigue life of air-entrained concrete at early stages of deterioration. Concrete cylinders were prepared with 0.45 and 0.65 water to cement ratios (W/C), then cured for 28 days before being subjected to the freeze-thaw cycling. After 0, 25 and 50 freeze-thaw cycles, the pressure tension (PT) test was used to induce tensile fatigue loading cycles until failure. The PT was capable of determining the decrease in fatigue life, represented as the number of cycles to failure, of the concretes when subjected to pure cyclical tensile loading after having first been exposed to freezing and thawing cycles. The results indicated that even though the ultimate static tensile strength of the specimens did not vary significantly due to the freeze-thaw cycles, the residual fatigue properties were degraded. UPV monitoring was able to determine the increase in internal damage, as the UPV of the specimens decreased with continued freeze-thaw cycling. It was shown that freeze-thaw deterioration reduces the ability of concrete to withstand cyclic loading, even at early stages prior to a decrease in static tensile strength.