DRMS for the mechanical characterization of lime mortars: Influence of user-controlled variables on the correlations between UCS and drilling results

The paper investigates the influence of the user-controlled variables on the results of the drilling test (DRMS) performed on lime mortars used for ancient buildings restoration. In particular, the ratio of the penetration and rotational speed (?), namely the depth of cut per revolution, is considered. The experimental results show a relevant variation in the shapes of the drilling profiles with ?, especially in mortars with lower strengths. The efficacy of the regression models between the uniaxial compressive strength (UCS) and the drilling results changes with the depth of cut. An optimal range of ? to perform the DRMS test is identified for the analyzed mortars. The paper also investigates the possibility of performing the DRMS test according to another procedure poorly studied in the literature to evaluate the UCS of materials. It consists of making more holes in the same material at different values of ?. This method is based on the analytical and experimental results obtained with another scratching technique, the scratch test. The statistical analysis of results shows that the correlation between the mean of the drilling forces and ? can be described by linear regression in a limited range of ?. The slope of the linear regression has a high correlation with UCS. The obtained positive results move to deepen the experimental research on this topic.