Tensile behaviour of early age concrete: New methods of investigation

The assessment of the tensile properties of early-age concrete is essential for reducing the risk of cracking due to restrained shrinkage. The tensile strain capacity of concrete, which was defined as a measure of the ability of the material to withstand deformation without cracking, is useful but few data can be found in available literature and the measure of the displacements of concrete is sometimes questionable. New direct tensile testing apparatus and experimental procedure were designed to provide reliable data on concrete specimens. The measure of displacements was deduced from digital image correlation. They enabled determining a stress strain relationship of concrete before cracking. The results showed a very rapid increase of strength from the end of setting. The evolution of the tensile strain capacity showed a minimum corresponding to the period that includes the setting time and early hardening, thus this is a critical stage for plastic shrinkage cracking. Even if the values are closely linked to the boundary conditions and experimental procedure, the effect of aggregate type could be investigated. (C) 2014 Elsevier Ltd. All rights reserved.