Читать книгу Monument Future - Siegfried Siegesmund - Страница 349

For quality control of stone-masonry conservation, an innovative ultrasonic device has been developed jointly with Rolf Krompholz (GEOTRON-ELEKTRONIK) within the EK FP7 Stonecore project.

The device consists of two probes: an US transmitter and receiver. They were basically designed to be inserted into holes of 20 mm in diameter drilled into the investigated surface layer at a distance of up to 100 mm from their centres and a depth of up to 60 mm. Certain design features (a flat base and adjustable rods for the transmitter and the receiver) allow for reproducible insertion of the device into prepared holes in order to acquire a reliable series of measurements for the investigation of changes in material characteristics. The device is portable and fully compatible with ultrasonic laboratory equipment, e. g. UKS 12 or UKS 14 Geotron Elektronik.

The device is robust and well-engineered for problematic outdoor measurement conditions. It is possible, for the first time, to measure the properties of materials in situ with an acceptable impact. The main advantage over the standard drilling technique is that it is possible to monitor the conservation effect during the intervention process because changes can be measured at an identical place and over the same volume of material after individual impregnation steps. This allows restorers to continue or terminate impregnation repetitions in response to the measured impact, i. e. consolidation depth and expected strengthening effects. In such cases, optimum control of conservation and reasonably low material consumption are desirable.

The device can be adapted for measurements across the dimensions of entire stones with holes drilled in joints, as this may be more acceptable on historic stone facades. During such measurements, the probes are fixed in a special rail rig allowing for longer distances between them and providing their firm fixture in the holes.

Figure 1: The double probe scissors set up with the UKS 14 ultrasonic testing system.

Figure 2: US measurement across the whole length of an ashlar block with probes inserted into holes drilled in the masonry joints.