Experimental study of the FRP-clay interface subject to normal stresses / Studio sperimentale dell'interfaccia FRP-laterizio soggetta a tensioni normali

The paper presents a campaign on testing solid clay bricks, with externally applied FRP reinforcements, carried out at the Department of Structural and Transportation Engineering of the University of Padova. The adopted procedure consists in performing three types of mechanical test on the same clay element: more precisely, a three-points bending on the intact brick, a compressive test or a splitting tensile test on one of the two portion produced by the flexural failure, and two pull-off tests on the other clay portion, after the application of a layer of FRP textiles. Two types of solid clay bricks have been used: extruded bricks coming from three different sets of the same manufacturer and facing ones produced by two other manufacturers; carbon fibers (CFRP) and glass fibers (GFRP) have been applied by means of an epoxy matrix as reinforcement. Therefore, three values of mechanical properties connected to the same masonry unit were obtained. On the basis of the first results, the possible relations between the pull-off strength and each of the other parameters (flexural, compressive and splitting tensile strength), were investigated, taking into account the variation of the clay substrate, the type of fibers (carbon or glass) and the presence, or not, of a layer of primer. Moreover, the possible correlations among the average properties (flexural, compressive and splitting tensile strength) of the bricks tested during the present campaign and during previous experimental activities performed at the University of Padova, were investigated.