Tests on materials and strengthening techniques

The increasing availability of new materials often leads to the use of strengthening techniques that do not have a wide experimental background, therefore requiring careful controls. These regard the compatibility of the materials that are expected to use with the existing ones in particular but also the correctness of execution techniques and the reliability of intervention results.

It is important, in these cases, to test site operations with accurate experimental controls whose extent has to be properly calibrated in relation to the sensitivity of the site and the importance of the intervention.

Laboratory tests must be primarily to assess the compatibility of new materials with the ancient ones, so as to avoid the occurrence of harmful chemical reactions within the materials which make up the structure. Due to the fact that masonry is, in general, a weak material, the tests have not identify the strongest  material  (in  this  regard  the data provided by the manufacturers are usually sufficient), but they have to identify the most suitable material.

The subsequent analysis of the correct on site working procedures is crucial, though often neglected. For example, in the case of grouting techniques, in many cases the masonry merely cannot be injected because it does not contain a cavity of adequate size (compared to the characteristics of grouting material e.g. particle size, fluidity etc..) or because it not has open porosity that allows the inner spreading of injected material.

On the contrary, the existence of over sized hollows or the use of fluid mixtures may cause the dispersion of the grouting material or its unexpected leakage with consequent damage to the surfaces of the building and inefficacy of the strengthening.

Therefore it is necessary to provide tests to verify the adequacy of the operative methods of the intervention too. These must be carefully planned and supported by diagnostic techniques such as drillings, samplings and video-surveys in order to evaluate the state of the masonry before, during and after the intervention.

Finally, also the efficiency of the project must be assessed because of the great variability of the base material and of the initial conditions of the building, that, in many cases, make the effects of the strengthening techniques uncertain. Also in these cases, it is necessary to carry out tests on the structures before and also after the execution of the interventions. A combination of different testing techniques is suggested in order to obtain an objective and measurable check of the efficiency of the proposed strenghtening techniques.