It is well known that the creep of concrete is influenced by the ambient relative humidity. But there is no sufficient information about the effects of moisture content in concrete specimens at the loading age on the creep behaviour and other mechanical properties. This experimental program was carried out to investigate the effects of moisture content on the strength and creep of concrete under uniaxial and triaxial (i.e. hydrostatic pressure) compressive stress at 30°C. And the dependence of moisture content on the visco-elasticity of concrete was discussed rheologically. The compression creep tests were performed under the following conditions; the moisture contents were 100% (wet), 68, 44, 14, 0 (dry) and -4% (over dry), and the creep stresses applied to the sealed concrete specimens were 100, 200 and 300 (kgf/cm2).
The test results showed that the compressive strength, Fc and the elastic strain, εc of concrete decreased with increasing moisture content, φ. It was considered that the strength reduction may be due to the change of surface energy, γ in the hydrated cement gel, and the larger elastic strain at lower moisture content level was brought in as the result of growing of void and crack in concrete during drying procedure. On the other hand, the moisture dependency of creep strain, εc was greatly different from the case of elastic strain: the magnitude of creep strain increased rapidly with increasing moisture from 0% to 40%, and then became nearly constant in the range of 40% over. From these facts, it was considered that the refraction point at 40% moisture in the (φ-εc) curve was brought by the repulsiveforce disjoining pressure which acts among many gel particles.