Effects of the thermal conditioning on the mechanical properties of an FRCM (FRiber Reinforced Cementitious Matrix) strengthening system

Fiber reinforced composite materials are starting to have very widespread use for rehabilitation and strengthening of existing concrete structures. As demonstrated by several experimental results, the use of composites made with fibers and inorganic matrix (such as cement based or lime based matrix) is very useful from a mechanical point of view. The performances of existing reinforced concrete structures strengthened in bending and shear with FRCM systems evidenced a significant improvement both in strength and ductility. The durability of FRCM strengthening systems are not adequately analysed; due to a limited number of experimental studies and research carried out. Moreover, the effects on the environmental conditions on the mechanical properties of strengthening systems are not well investigated. In this paper, the effects of the thermal conditioning on the mechanical properties of the FRCM system was experimentally investigated. The examined strengthening system consists of PBO (short of Polyparaphenylenebenzobisthiazole) fabric meshes embedded into a cement-based matrix. The system was exposed to thermal cycles at different temperature values (100 and 200 °C) and, then, tested to evaluate its mechanical properties (ultimate strength, ultimate strain and elastic modulus). Five thermal cycles were developed by daily exposure of PBO fabric mesh, matrix and PBO-FRCM specimens at constant temperature value, over six hours and subsequently cooling down freely to ambient temperature (20 °C). After the thermal treatment, specimens were tested until failure, at room temperature. Results of tests analysed in terms of stress–strain relationships allowed influence evaluation of the thermal treatment on the structural response of PBO fibers, matrix and PBO-FRCM specimens.