Assessment of the European Standard for the determination of resistance of marble to thermal and moisture cycles: recommendations for improvements

The bowing phenomenon is so relevant that two projects, EU funded, from 1999 studied it and a European Standard to assess the resistance to thermal and moisture cycles (influencing bowing) has been recently adopted. In particular, according EN 16306: 2013, measurements of bowing and flexural strength should be performed before and at the end of the ageing cycles. Additional non-destructive tests are recommended, but are not compulsory for the standard. Moreover, Annex A of EN 16306 contains guidance on the limit values for the selection of marble types suitable for outdoor uses, especially façade applications. Eleven varieties of marble have been tested by means of this laboratory ageing test. Non-destructive tests such as the measurements of ultrasonic pulse velocity (UPV), adjacent grains analysis, open porosity, and water absorption have been executed together with the conventional flexural strength test. The results obtained from image analysis on thin sections indicate that the AGA index may not always be correlated with the other tests: amount of bowing, loss of flexural strength, or loss of UPV. Some consideration of the decrease in mechanical resistance and the bowing in relation to the variety of marble tested and the limit values indicated in Annex A of EN 16306 can be noted. It is known that bowing and rapid strength loss occur in some varieties of marble when used as exterior cladding and other exterior applications. Additional conclusions have been drawn: bowing and flexural strength correlate well and can be used to assess the suitability of the marble to be employed in outdoors.