Interpretation formulas for in situ characterization of mortar strength

The in situ characterization of mortar mechanical properties is a mandatory activity in every structural assessment of existing monumental buildings. Fine and complex numerical models are meaningless if the material parameters are hypothetical or based on reference values since there exist thousands of mortar compositions and brick types and aging processes do change values in a not easily predictable way. Therefore direct investigation of the mortar courses is a key ingredient, and this requires specific tools able to deal with thin layers of materials and requirements of conservation. There are however several ways able to investigate mortars without extracting consistent specimens, and most of them can be interpreted within the common framework of a Mohr-Coulomb plasticity constitutive behavior. Several of these techniques are even capable to discriminate superposed repointing layers of sufficient depth. In the paper, some versatile and effective mortar investigation techniques are reviewed and the formulas for the strength class definition are presented. Then, the predictive ability of the proposed formulas is checked against large experimental campaigns. Finally, an interesting investigation on the Ponte Taro bridge in Parma is used in comparing the results of different experimental tools. The data show a general good agreement among the mechanical properties extracted with the proposed procedures.