Читать книгу Monument Future - Siegfried Siegesmund - Страница 107

Collapsed blocks measuring 21x20x50 cm were taken from the site and samples were obtained from both the unaltered and altered portions, having yellow-beige (Y) and reddish colour (R), respectively (Fig. 2).

The following analyses and tests were performed.

— Thin-section samples were observed in plane-polarised and cross-polarised transmitted light by means of an optical microscope (Eclipse LW100 Nikon) at magnifications of 50x e 100x.

— X-Ray Diffraction analyses (XRD) were performed on both the whole rock and insoluble residue. The insoluble residue was separated by a chemical attack of the grinded stone with HCl-3N in order to remove the carbonates by dissolution. A Philips 1742 diffractometer (APD – 3.6j version) was used for the analyses (CuKα, 40 kV, 20 mA, 2ϑ step size of 0.02 °, counting time 1.25 s, scan interval between 3 ° and 60 °). The diffraction data 79were processed with a X’Pert software — Philips Analytical.

— Simultaneous thermal analyses by Differential Scanning Calorimetry and Thermogravimetry (DSC-TG). A Netzsch STA 449 F3 Jupiter^® was used. Both samples of the whole rock and of the insoluble residue were analyzed. Approximately 25 mg of each powder sample were heated in air from the ambient temperature to 1,000 °C, at a heating rate of 10 °/min.

— Colour changes were recorded by colorimetric measurements. These were taken by light absorption in diffuse reflection using a Konica Minolta CM700d spectrophotometer. They were carried out with a D65 illuminant and under a 10 ° standard observer. L*, a* and b* colour coordinates in the CIELab system were measured and the colour variation (ΔE*) was calculated.

— Measurements of bulk density, porosity accessible to water and water absorption amounts of the stone samples were performed through saturation and buoyancy techniques, following the ISRM recommendation [ISRM, 1981].

— Ultrasonic Pulse Velocities (UPVs) were measured on specimens (cubes 70 mm side obtained from masonry blocks coming from the site) after drying at 70 °C, according to ASTM D2845-05 (ASTM 2005). In particular, three visible unaltered (Y) and three colored specimens (R) were taken from the collapsed portion of the building. Velocities were measured by direct transmission method using a TDAS 16 (Boviar) instrument and probes with a frequency of 55 kHz. They were recorded in each direction (x, y, z) of the cubic specimens and expressed as mean values.

— Compressive strength tests were performed according to UNI EN 772-1 (UNI 2011) on the same specimens used for UPV test, after drying at 70 °C. A universal testing machine (Metrocom Engineering spa), with a load capacity of 200 kN and a speed of 0.2 mm/min, was used for the test.