Nuclear magnetic resonance as a non-destructive analysis for the study of a new stone consolidation treatment

Limestone, used in artistic and architectural fields because of its composition and textural characteristics, is particularly susceptible to decay. Its constant exposure to a combination of weathering factors, causes an increase in porosity and a loss of material cohesion. In order to deal with this deterioration process, Ca(OEt)2 as a novel product developed during the EC NANOMATCH project, is tested to consolidate four types of limestone widely employed within Italian Cultural Heritage: Noto stone, Lecce stone, Carrara marble and Vicenza stone [1]. Pore-space properties, such as pore-size distribution and connected porosity, are crucial factors in the evaluation of a consolidation product and, throughout this study, they are analysed with NMR relaxometry of water 1H nuclei. This technique, being both non-destructive and non-invasive, is able to obtain both longitudinal (T1) and transverse (T2) relaxation time distributions of water in the stones' pores, before and after the consolidation treatment [2]. The results demonstrate that T2 is more sensitive than T1 in detecting pores of small dimension for all lithotypes, but not for marble which gives results that are not easily legible due to its low open porosity and a small quantity of absorbed water. Combining relaxation data and micro-structural studies performed by MIP and SEM measurements, a better understanding is obtained of the changes within stone porosity. The results confirm that NMR technique could be a useful tool for the evaluation of consolidation treatment on stone.