Effect of post-tensioning on the bending behaviour of mineral matrix composite beams

The objective of this paper is to analyse the feasibility of using composite beams made of high performance fibre reinforced mineral matrix as structural elements. The mineral matrix is an inorganic phosphate cement (IPC), in which E-glass fibres and fabrics are used as reinforcement. Post-tensioning was studied as a way to improve the bending and shear behaviour of beams. Longitudinal compression and 4-point bending tests were carried out on three types of beams: centrally, internally and externally post-tensioned. The validity of fundamental principles of post-tensioning technology was investigated by performing global and local analysis of the behaviour of these beams. The strain levels, corresponding to different thresholds of post-tensioning loads, were assessed by analysing strain superposition principles. The experimental results showed a reduction of the risk of cracking and limitations of the deflection and of the acting shear force. The post-tensioning generates a translation of the initial strain to the compression field and produces a linear strain distribution, as opposed to that of flexural strain. Moreover, in the case of external post-tensioning, it was possible to choose an adapted eccentricity of the tendon profile to optimise the effect of the post-tensioning on the deflection and on the acting shear force.