Interpretation of experimental tests on small specimens of historical mortars.

The experimental characterization of mortar in historical masonry constructions is a difficult task. Entire units or unit samples can be extracted, without deteriorating excessively the masonry member. The mechanical properties of bricks can be obtained from standard tests with sufficient precision. On the contrary, the difficulties in the assessment of historical mortars even arise from the extraction of appropriate specimens. If it is possible to take undisturbed mortar samples, they can be subject to punching test to deduce the compressive strength. The test results account for the joint thickness effect that cannot be neglected during the estimation of masonry strength. Another possibility is the extraction of small specimens including both bricks and mortar, using a common core drill. This activity is suitable for historical buildings, since it does not inflict severe damage. The cores can be subject to splitting tests with particular setups, providing 30°, 45° or 60° inclinations of the mortar layer with respect to the loading plane. This test induces a mixed compression–shear stress state in the central mortar layer. In this case, the confinement effect exerted by units on the mortar layer can be regarded. This work presents the interpretation of experimental tests on small specimens of historical mortars. Different test setups have been considered, in order to analyse the material subject to different states of stress. The actual interpolating failure envelope has been estimated. The analytical interpretation of the experimental results can be helpful to determine the input parameters for numerical analyses.