Experimental and Analytical Study of Creep and Shrinkage in Early-Age Concrete

The magnitude and rate of development of early-age deformation of concrete is often not known reliably and restraint to shrinkage is often poorly modelled in structural design. In order to accurately quantify the early-age deformational characteristics of Australian concrete, including shrinkage and tensile creep, a comprehensive experimental program is underway at the Centre for Infrastructure Engineering and Safety at UNSW Australia, where a series of experiments have been performed to quantify the early-age properties of concrete. A restrained cracking test was devised and reinforced concrete prisms were tested in tension under sustained loading to measure tensile creep and restrained shrinkage. Free shrinkage was measured on companion unreinforced prism specimens. Dog-bone shaped specimens were also tested in direct tension in portable creep rigs. All the specimens were tested at a stress-strength level of 50 % of the tensile strength of concrete at the age of 2 days. It was found that RC prisms cracked with time under sustained tension before reaching the instantaneous tensile strength of concrete. A strength reduction factor of 0.7 and 0.87 was observed based on split tensile strength and direct tensile strength, respectively. Tensile creep coefficients calculated from tension prisms agree well with the tensile creep coefficients of dog-bone shaped specimens.