Abstract
Cementitious materials are characterised by low tensile strengths and low tensile strain capacities. They are brittle and, as such, benefit from reinforcement, which increases their ability to withstand tensile and shear stresses. The mechanical performance of cheap, lightweight, aggregated cement sheets can be improved significantly by incorporating fibre meshes just beneath either surface. Such "cement-boards" have potential for use in several load-bearing and non-load-bearing applications, in both interior and exterior construction environments. For this to be possible, it is necessary to develop an understanding of the manner in which these materials fail and to be able to predict the properties of the composite in terms of those of its constituents. In the present work, a commercially available cement board and several experimental boards have been examined using reflected light and scanning electron microscopy, enabling the main micro structural features to be characterised. A methodology for producing damage free specimens for mechanical characterisation has been developed. A bend rig suitable for the testing of specimens up to 0.5 m in length and 70 mm in width, in three or four point bending, has been designed and built. The properties of the boards have been measured in flexure and in tension and the relevant failure mechanisms have been identified. Also, the properties of the glass fibre crenette and the cement core from the boards have been measured individually and the effect of the accumulation of damage in reducing the Young's modulus of the commercially available board has been studied and modelled analytically. It was found that the stiffness of the cement board is dependent solely on the properties of the cement core, while the ultimate strength is dependent on the properties of the crenette. The geometry of the crenette has an influence on the manner in which the cement board fails.