Mechanism of Tensile and Compressive Unequal Creep of Hydraulic Concrete Based on Variations in Pore Structure

To elucidate the mechanism of tensile and compressive unequal specific creep of hydraulic concrete, tensile and compressive cyclic loading and unloading creep tests were carried out under uniform test conditions. Concrete slices obtained by cutting after creep testing were analyzed to determine the overall saturation and porosity of the tensile, compressive, and companion specimens. In addition, the porosity and pore-size distribution of cement mortar of the tensile, compressive, and companion specimens were obtained by mercury-intrusion porosimetry. The results of the tensile and compressive creep of hydraulic concrete tests show that the tensile specific creep exceeds the compressive specific creep under uniform test conditions. The overall saturation and porosity of the tensile and compressive specimens are nearly equal, which is inconsistent with seepage theory (i.e., that compressive creep facilitates water extrusion more than tensile creep). Given that microcracks develop parallel (perpendicular) to the direction of compression (tension) under compressive (tensile) stress and that concrete has high compressive strength and low tensile strength, more microcracks develop in the tensile creep specimens than in the compressive creep specimens, resulting in a greater tensile specific creep than compressive specific creep.