Shear Behaviour of Engineered Cement-based Composites
Some experiments utilizing the shear capacity of Engineered Cement-based Composites (ECC) have suggested that elimination of shear reinforcement is feasible when the concrete matrix is replaced by ECC. However, actual application and more rigorous cost analysis are prevented by the fact that the shear stress and strain properties of ECC have not yet been characterized as accurately as the tensile properties. This study focuses on the investigation of the shear property of ECC. The study starts with a survey and comparison of existing shear tests for composite materials. The Iosipescu shear test concept is chosen as the most objective method for ECC, and subsequently, modified for specific application on ECC by simple analytical design and finite element refinement. The modified Iosipescu shear test method is applied on, four types of ECC specimens with different fibre content (0%, 1%, 2%, 2.5% by volume), which have been cast in specially designed moulds and cured in laboratory conditions. Three phases of shear measurements are used to check the shear test appropriateness and study the shear mechanical properties of ECC. The failure mode is verified in the first phase, detailed measurement of the shear strain and shear stress is performed and recorded in the second phase, and in the third phase more information about the ductility of diagonal cracking is obtained by measurement of the tensile principal deformation. By also conducting direct tensile tests on specimens of the exact same mix, information of both uniaxial tension and shear behaviour is available, from which elastic and shear moduli, as well as Poisson’s ratio of ECC are computed. A first step toward application of this knowledge of the shear behaviour of ECC is taken by studying the response of shear-dominated beams and beam-columns of reinforced concrete and reinforced concrete combined with ECC as the outer crusts. These beams were prepared and tested by other members of the research group of the Division for Structural Engineering of the University of Stellenbosch. It is shown that ECC can indeed successfully replace shear reinforcing steel, due to its shear capacity.