Laboratory assessment of the FRP to timber bonding force for ancient beams showing biological attack

The evaluation of the in situ mortar properties of old masonry is a very complicated task. Moreover, the properties of the masonry can be rarely inferred by the test of a triplet specimen extracted from a wall, mainly for lack of viable sampling points. A viable alternative is based on the use of brick cores including a central mortar layer lying on a diametrical plane. In fact these specimens can be extracted very easily by cutting cores spanning two bricks at least. The obtained core is then subjected to a splitting test with a set up providing a 45° inclination of the mortar layer with respect to the separation plane. This type of test is similar to a diagonal wallet test and induces a mixed compression – shear stress state in the central mortar layer. By using a Mohr – Coulomb failure criterion the test result can be interpreted in order to obtain all the compression and shear properties of the masonry. In particular, by assuming a friction angle based on the compression to tension strength ratio of the mortar, the cohesion can be evaluated, and in turn, all the other constitutive parameters. In the paper a consistent set of experimental tests is examined which gives experimental evidence that the results of the rotated layer splitting tests are in good agreement with other analytical and experimental procedures.