Abstract: Concrete strain is an important physical quantity for quantitative characterization of concrete deterioration under freeze-thaw cycling, but previous freeze-thaw test methods are difficult to reflect the strain evolution law of unsaturated concrete under different minimum freeze-thaw temperatures. We design and conduct sealed freeze-thaw tests and water-freeze-thaw tests on the hydraulic concrete specimens in four different saturation ranges (70 - 80%, 85 - 91.7%, 91.7 - 95%, and 95 - 100%) and three different freeze-thaw cycling temperature ranges (-18 to 6 ℃, -10 to 6 ℃, and -5 to 6 ℃). Based on the strain measured by strain sensors embedded in the specimen, we examine the strain evolving process of hydraulic concrete during a full cycle, including variations in its residual strain, thermal expansion coefficient, and frost heave coefficient at different saturations and different minimum freeze-thaw temperatures. The results reveal that as the cycling number increases, a continuous and irreversible deterioration leads to the freeze-thaw damage of unsaturated sealed freeze-thaw specimens and water-freeze-thaw specimens. And the residual strain of the latter specimen set is larger than that of the former set, and the higher the saturation, the greater the residual strain. The thermal expansion coefficient varies slightly with the cycling number, and the freeze-heave coefficient increases with saturation and the cycling number. The difference of these two sets in thermal expansion coefficients is relatively small, while the frost heave coefficient of the water-freeze-thaw set is significantly greater.

Key words: unsaturated hydraulic concrete, freeze-thaw damage, residual strain, coefficient of thermal expansion, frost heave coefficient