The effect of saturation coupled with loading rate on the tensile strength and the compressive mechanical properties of concrete, namely static and dynamic strengths, Young's modulus and critical strain, were studied by splitting and uniaxial compression tests respectively. The experimental results indicate that the static tensile and compressive strengths of saturated concrete are lower than those of concrete in dry state, but the dynamic strengths of saturated concrete is higher than those of concrete in dry state. The difference increases when the loading rate increases. Based on physics and cracking rules of concrete, physical explanations on the effect of saturation and loading rate on the concrete strength were given with the consideration of the harmful and favorable effects of free water in the cracks. In addition, proving experiments were also carried out to investigate that whether the state of water in the cracks affects the surface energy of solid, and the results showed that surface energy was valid to explain the variation of tensile strength of concrete.
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