Uniaxial tensile creep and failure of concrete
The work in this thesis consists of a study of the behaviour of concrete under uniaxial tension with regard to both strain development under external loading and short- and long-term failure. A method was first developed for the accurae short- and long-term uniaxial tensile testing of concrete and has been applied throughout the investigation. As a result of this work, a mechanism has been proposed within a framework of a seepage-plastic the tensile creep and failure of concrete. A rheological model has also been suggested to describe this mechanism. The tensile creep of air drying concrete was larger than that expected in compression but smaller when the concrete is stored sealed or under water. The creep of sealed and immersed concrete reached limiting values within two months while that of air drying concrete continued for a much longer tie. in other respects tensile creep behaviour was similar to that in compression.The creep of sealed concrete was about half that of immersed concrete and as low as 0.1 of that of air drying concrete. A relationship has been obtained between ultimate strength and the period of sustained loading. This relationship is similar to that previously obtained for concrete in compression but the reduction of strength due to long-term loading is greater than than for compression and can be up to 50 per cent of the short-term strength. This relationship is considerably influenced by the storage conditions of the specimen and the type of aggregate employed. The long-term strength of sealed concrete has been found to be up to 50 per cent higher than that of water-immersed concrete made with gravel aggregate while the short-term strength was about 15 to 20 per cent higher. This was not found to be so for concrete made with crushed granite aggregate. A limiting positive ultimate strain of 70 to 90 microstrain due to external loading was observed for all gravel concrete tests, short- or long-term but higher values were measured on granite concrete.