Tracing of decay profiles and evaluation of stone treatments by means of microdrilling techniques

The recent development of a new drilling machine in the framework of the EU project HARDROCK brought some interesting perspectives for the characterisation of decay profiles, for tracing old consolidating treatments and for evaluating new consolidants. The equipment executes a drill hole, typically 5 mm in diameter, down to 5 cm, under precisely defined and controlled drilling conditions. The output is a graph of force versus depth. The instrument can be transported and operated in situ. The operator defines the drilling rotation speed and the advancing rate and the instrument registers the force required for executing the hole under those strictly defined conditions. This paper presents some data taken from a laboratory study on consolidants which demonstrate that the equipment has a very high discriminating power for detecting the presence of consolidants. Clear differences among some typical consolidants were detected, both in the strength increase and in the penetration depth. They also show that the average drilling forces present a fairly good correlation with bending strength, in spite of the fact that full consolidation of the tested specimens was not possible with all consolidants. The in situ study of Porta Especiosa has shown that the instrument was able to identify the presence of decay events at several depths, in a way that no other known method can do. The identification of the presence of old treatments was demonstrated with total guarantee.