Polypropylene fibre reinforcement of hardened cement paste
This thesis considers the tensile deformation characteristics of polypropylene fibre reinforced hardened cement paste having heterogeneous fibre geometries and a range of volume concentrations. Polypropylene fibres were prepared under various manufacturing conditions using a laboratory extruder, to ascertain the effect of these conditions on fibre characteristics. The relevant properties of cement paste likely to influence the polypropylene fibres and the eventual composite were investigated. An investigation of continuous aligned fibre composites in tension, containing various volume concentrations of fibres, showed that multiple cracking occurred despite the elastic modulus of the fibre being considerably lower than that of the hardened cement paste. Factors which enabled fibre/matrix contact to be maintained during the multiple cracking process, despite the unfavourable Poisson's ratio of polypropylene, were considered. Discontinuous aligned fibre composites were tested in tension, to ascertain the effect of volume concentration and length of fibres on the shear stress transfer between fibre and matrix and on multiple cracking. Composites containing parallel fibres, with fibre directions at varying angles to the direction of applied tensile stress, allowed an assessment to be made of the role of inclination. Crack distributions, pull-out behaviour of fibres and the ultimate stress of composites were investigated. Finally, random fibre reinforced composites were evaluated to provide a comparison with the Continuous, Discontinuous and Inclined fibre reinforced systems. In addition to determining the mechanical deformation of the various composites, the acoustic emission associated with internal deformation mechanisms was studied. This was undertaken with equipment capable of monitoring a range of acoustic pulse parameters.