Читать книгу Monument Future - Siegfried Siegesmund - Страница 249

Penetrometer gives information about the conditions of preservation and homogeneity of a mortar. The penetrometer consists of a striking mass connected through a spring to a striker, in which a pin is inserted. The pin, subjected to constant dynamic shocks advances inside the mortar joint which pushes and compresses the mortar along its path.

The resistance that the mortar offers to the pin advancement is proportional to the mechanical strength of the material (Łątka and Matysek, 2018). The pin is made of steel, has a diameter of 3 mm and a conic tip at an angle of 25°.

The instrument used is a Penetrometer RSM-15 Version 0.1 of Diagnostic Research Company (DRC Srl) and it is supplied with a KIT including a striker, an automatic measuring body, a manual comparator, a series of tips and measuring tips and support accessories for measuring driving depth. The impact energy is 4.55 Nm, the impact mass is 835 g and stroke of 82 mm.

The result is the needle penetration depth (RPMs, mm), after a number of impacts defined according to the type of procedure used (in the study case 10 impacts). It’s possible to calculate the compressive 169strength (R, in MPa) with a correlation curve and equation of the instrument [1]:

R = 4.489exp^–0.106RPMs [1]

In the case studies two penetrometer tests on each core sample were carried out. The test was executed verifying previously the length of the initial steel needle L0 (80 mm), then applying n. 10 impacts, removing the penetrometer, leaving the needle in the mortar and calculating L10, the length of the needle outside the mortar and finally calculating the absolute penetration depth [2]:

RPMs = L0–L10 [2]