Shear behaviour of polyolefin and steel fibre-reinforced concrete

Abstract

Since the first appearance of concrete, various approaches have been taken in order to improve the behaviour of the material when subjected to tensile and bending stresses. Such approaches have provided enhancements in the ductility of the composite material. One of such approaches entails the addition of fibres in the concrete bulk mass. This has been employed in everyday practice in slabs, precast tunnel linings and pipes for more than 50 years. The contribution of fibres to the mechanical properties of concrete enable, if certain requirements are complied with, a reduction or even substitution of the steel bars found in reinforced concrete. The contribution of fibres to structural design can be contemplated only if several conditions are met. Such conditions are established by certain recommendations, with the Model Code 2010 (MC2010) being the most widely accepted. MC2010 describes the residual stresses that should be borne by the fibre-reinforced concrete (FRC) when performing three-point bending tests on notched specimens, assessed according to EN-14651. Shear stresses should also be taken into account in the structural design. In addition, fibres might contribute to the shear strength of the FRC. However, at the time of writing there has been little published research regarding this. This contribution seeks to improve the current state of the art concerning the behaviour of FRC with steel (SFRF) and polyolefin (PFRC) fibres subjected to fracture under mode II condition. Both fibres are considered as structural ones in several concrete national codes and regulations. In order to do so, an experimental campaign was designed based on shear push-off tests. Conventional monitoring techniques were complemented with digital image correlation (DIC) systems. DIC permitted detection of the onset and development of cracks during the tests, featuring the cracking patterns of SFRC and PFRC subjected to shear stresses. The results showed that changes in the fibre type modified the mechanical behaviour of the materials studied. Moreover, the ductility of SFRC and PFRC alike were assessed and the fracture energy obtained. The combination of the conventional measuring techniques and DIC allowed correlation of the cracking development with the mechanical behaviour during the test.