Tensile behavior of FRCM coupons under thermal stresses

Fiber Reinforced Cementitious Matrices (FRCM) represent a very efficient strengthening solution for the improvement of the structural behavior of existing masonry constructions. However, the mechanical performances of these materials could be significantly affected by different environmental conditions, such as the exposure to thermal stresses. This aspect should be properly assessed for a correct design of the strengthening interventions. The Italian Guidelines for the identification, qualification and acceptance control of FRCM systems to be used for the structural strengthening of existing constructions prescribe the execution of direct tensile tests on FRCM coupons to evaluate the behavior of these composite systems subject to thermal stress. Within this framework, the objective of the present research is to evaluate the effect of a thermal stress on the tensile behavior of three different FRCM systems, composed by steel or basalt fibers and lime-based or cement-based mortar matrix. Tensile tests are performed, for each system, on samples at ambient temperature (22°C) and on samples conditioned at 80°C for six hours, according to the indications provided by the Guidelines. The test results show that the effect of the thermal stresses is more evident in the first phases of the tests, i.e. during the elastic phase and the mortar matrix cracking phase, while it is less significant in the last phase, which is related to the fibers behavior. The tensile strength of the investigated FRCM systems is, indeed, within the limits provided by the Italian Guidelines, while the curves of the conditioned samples may deviate from the reference ones at the beginning of the tests. These findings are critically discussed within the paper.