Creep and Shrinkage of High Strength Concrete

Abstract

High strength concrete (HSC) has revolutionised the construction industry in the 1980's and Australian researchers, consultants and contractors have been very active in this area. However, most major codes for design and construction with concrete are applicable only to normal strength concrete (f'c < 50 MPa) and are based on research on normal strength concrete (NSC). High strength concrete has an increased strength and modulus of elasticity which allows a larger stress to be applied. When stress is applied to a concrete member strain will occur. The initial strain is elastic and can be recoverable when the stress is removed. The total strain of a concrete specimen is the sum of elastic, creep and shrinkage strains. Creep although not critically affecting a structure is responsible for cracking and deflection. The volume changes in concrete due to shrinkage can also lead to the cracking of the concrete. It is therefore important to know the creep and shrinkage phenomena in HSC. In order to investigate the creep and shrinkage behaviour of HSC, creep and shrinkage specimens were cast using concrete of 3 different strengths namely 45, 80 and 100 MPa and creep and shrinkage strains measured. The obtained results are compared with five published creep and shrinkage models most of which are meant for NSC. The preliminary findings indicate that they are not quite applicable to HSC and there is need for the development of new models for the prediction of creep and shrinkage in HSC.