Contribution of the drilling resistance measurement system to the characterisation of ancient mortars

Abstract eng:
The application of the drilling test on the characterisation of homogeneous stones is widely used, mainly on carbonate stones that are softer. The drilling revolution and penetration speed are important test parameters that are defined by the operator according to the hardness of the testing material. When in presence of heterogeneous materials composed of components of different hardnesses the choice of the operative drilling parameters is a problem and inevitably, the resulting drilling profiles are very irregular and of ambiguous interpretation. In this paper, the failure mechanisms that govern the cut during drilling and their effect on drilling profiles are discussed. The influence of operative drilling parameters in drilling results is also mentioned. A set of mortar compositions of medium-low mechanical resistance (compressive strengths ranging between 1 and 11 MPa) were produced and their mechanical properties were assessed through conventional compressive strength, ultrasonic pulse velocity and drilling resistance tests. Different drilling operative parameters were tested in order to find the most suitable ones for each composition. Results show that the drilling resistance measurement system is sensitive and reliable for in situ characterisation of weak binder mortars, but the accuracy of the results has to be frequently verified and if necessary, different operative drilling parameters have to be established to return the accuracy.

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