Читать книгу Monument Future - Siegfried Siegesmund - Страница 247

Mechanical characterization of stone materials (i.e natural stones, mortars, bricks) belonging to historic building is a very important issue for structural evaluation, prevention of risk and definition of best restoration practices. In practice it is very difficult to perform destructive test on single elements of masonry of historic building due to high cost and impact on constructions (Boschi et al. 2016; Del Monte et al. 2020).

The effort to have a sufficient amount of samples for the application of mechanical tests in laboratory (i. e. UNI EN 1015-11 2019; UNI EN 12504-1 2019; UNI EN 12390-13 2013; UNI EN 12390-6 2010) or the difficulty to reproduce exactly an ancient mortar with similar composition, microstructure and state of conservation, forces the use of in situ tests. Most of used methods (penetrometric, percussion or rotational techniques) provide data that are indirectly correlated to the strength through measurements like resistance to abrasion, to compression and to penetration, micro sandblasting, etc (Fratini et al. 2006; Yang et al. 2016; Pelà et al. 2018).

Microdrilling Resistance Measurement System is a micro-destructive static technique used in built heritage to assess the superficial cohesion of natural and artificial stone materials, both in laboratory 168and in situ. The instrument is constituted by a modified drill in which a load cell allows to measure drilling resistance of the material under examination, maintaining constant rotational speed and penetration rate (Delgado et al. 2002; Pamplona et al. 2007; Nogueira et al. 2014; Nogueira et al. 2018).

Mortar penetrometer is a dynamic penetrometer and is comparable to an adapted Schmidt rebound hammer, in which the impact plunger is replaced by a metal pin. In this type of test, calibrated impact mass is used to insert a metal pin into the mortar, measuring the penetration depth. This penetration depth corresponds to compressive strength of mortar according to a penetrometer correlation curve.

In this paper we performed both in situ and laboratory tests on ancient mortars in order to identify a correlation among data obtained with drilling and penetrometric techniques.

Similar attempt to correlate drilling measurements with non destructive techniques, was performed by Costa et al. 2010 and Noguiera et al. 2014, comparing DRMS data and ultrasonic tests, concluding that ultrasonic velocity, measured in direct mode, is in good agreement with the drilling results, although expressed by the average values of the distributions with great variations.