The use of sound velocity determination for the non-destructive estimation of physical and microbial weathering of limestones and dolomites

Two limestones from Crete, Greece and Mansfield dolomite from the UK were tested experimentally for their resistance against physical and microbial attack. XRD and SEM were used for the assessment of their mineralogy, original structure and weathering patterns. Stone discs subjected to physical, microbial and combined physical/microbial weathering simulation cycles were treated with distilled water, NaCl and Na2SO4solutions, alone or in combination with mixed microbial populations (MMP). Measurements of weight change, mechanical alteration and viable bacterial counts were augmented by the non-destructive technique of sound velocity transmission. Both longitudinal (Up) and shear (Us) waves velocities were mostly stable or slightly accelerated in the case of distilled water and NaCl treatments, but with the Na2SO4weathering regime, involving expansion due to hydration and dehydration, they decreased. However, a marked decrease was found whenever MMP were present. These observations suggest a possible contribution of microorganisms to physically induced deterioration of stone. Correlation of Upand Usto weight, other mechanical properties and bacterial counts highlighted the importance of surface hardness in predicting mechanical behaviour. Furthermore, the evidence suggests that porosity size might influence the type of stone attack and a possible contribution of sulphur bacteria to deterioration. Sound transmission velocity proved to be an effective diagnostic technique to assess the mechanical state of building stones.