Nondestructive rock porosity estimation by InfraRed Thermography applied to natural stones

The prediction of rock porosity through infrared thermography holds a high potential for non-destructive testing procedures for natural stones, but at the same time there are still few scientific experiences on its applicability on different rock types. In fact, although international standards on laboratory rock characterization allow the use of differently shaped and sized specimens, data available in the literature concern the application of this novel procedure only on cubical rock specimens, with promising results even in the perspective of a potential future standardization of the test. In this paper, motivated by the need for non-destructive analysis of construction and cultural heritage materials, 143 rocks were analyzed to study the reliability of infrared thermography on specimens with different geometries. Results demonstrate that the cooling rate within the first 10 min of test remains the most suitable index for the prediction of rock porosity. This physical property was further analyzed by separately considering the normal and the effective porosities against the rock cooling speed. The best statistical correlations were found for the prediction of total porosity, although satisfactory trends were achieved also for indirectly estimating effective porosity. According to four different sets of specimens, prediction equations were developed from statistical analysis. Achieved outcomes argue strongly for additional scientific research on this prospective test, with the goal to define a standardized, non-destructive, and quick alternative to the common procedures currently used in laboratory for measuring porosity.