Relaxation of concrete: A preliminary study on the influence of Initial stress-strength ratio and rate of stress loss

SMEC South Africa, 65 Riebeek Street, Cape Town, 8001, South Africa

Abstract

Tensile relaxation is important because of its role in mitigating the possibility of cracking in concrete under constant restraint. This is made possible by the reduction in the induced or applied stress over time. Gradually, the relaxation behaviour of concrete has become clearer in many ways despite the difficulty in testing and carrying out experimental work. In order to better understand the relaxation behaviour of concrete, this aim of this study is to investigate the influence of the initial stress-strength ratio on concrete in tension as well as the rate at which relaxation occurs. Tensile relaxation was determined using dog-bone specimens after 3 and 10 days of curing. Three water-binder ratios of 0.45, 0.55 and 0.65 were investigated respectively. After determining the tensile strength of the samples, they were placed under constant stress levels of 20%, 40%, 60% and 80% of the ultimate failure load. Results show that although the increase in initial stress-strength ratio increases the relaxation, there is no proportionality. The rate of stress loss is not influenced by either one of the parameters varied. While the study adds to our understanding of the relaxation behaviour of concrete, more detailed and longer duration studies are required to validate these findings while also considering the potential effects of micro-cracking.