Colour and ultrasound propagation speed changes by different ageing of freezing/thawing and cooling/heating in granitic materials

In the present work we determined the chromatic coordinates (L*, a*, b*) and ultrasound propagation speeds on the three spatial planes (Vx, Vy, Vz) of three ornamental granites (Aqueduct of Segovia, Spain) before, during, and after being subjected to 70 cycles of two types of accelerated ageing (typical of cold regions): a) freezing/thawing and cooling/heating (T1), and b) freezing/thawing and cooling/heating + salt crystallization (T2). A multivariate technique (Canonical Biplot) was applied to the data obtained, with the observation of significant variations between the two types of accelerated artificial ageing as compared with those obtained in quarry rock in the three chromatic coordinates (L*, a*, b*). With regard to the ultrasound propagation speed, we only detected differences in the results of the T2 artificial ageing treatment with respect to those of quarry rock. This fact is confirmed by the estimated data of resistance to compression.