Laboratory measurement of ultrasound velocity during accelerated aging tests: Implication for the determination of limestone durability

The non-invasive ultrasound propagation technique was applied in laboratory tests with thepurpose to evaluate the susceptibility to decay of stone materials.The 'Scicli' limestone was chosen as test material, since it is commonly employed as a building materialof baroque churches and historical monuments in South Eastern Sicily.Eight samples were subjected to several hydric and accelerated aging tests (salt crystallization) andduring these latter the longitudinal waves velocities were measured.The susceptibility of the rocks to decay was showed by the response to absorption/desorption and saltcrystallization tests; in particular high values of mass loss were recorded (up to 41%) and the decay ofthe already started during the 4th cycle.During salt crystallization a general decrease of P-waves velocity was observed in response to theoccurring of macro- and micro-fractures even if almost all the samples showed broadly irregularpatterns.The data obtained by means of hydric and petro-physical tests were subsequently assembled andprocessed for multiple regression analysis. The goodness of the results and the statistical relevance ofthe chosen variables was testified by the R2 values (0.99) and by the p<0.05 values respectively.Variables CA (capillary coefficient) and AB (absorption coefficient) resulted as the most importantpredictors of mass loss followed by variables linked to the ultrasound propagation indicating that thislatter is a suitable non-invasive technique especially when is coupled to a preliminary petrographicand physical characterization of the rock.