New insights in weathering analysis of anhydrous cements by using high spectral and spatial resolution Confocal Raman Microscopy

Raman spectroscopy combined with Confocal microscopy is a non-destructive technique that provides relevant structural information in materials. In this study, we present non-destructive Raman image and structural analysis of anhydrous cements with carbonation evidences by means of Confocal Raman Microscopy (CRM). The results obtained by CRM have been contrasted with the techniques commonly used for this purpose as FTIR and DTA/TG. CRM shows the main cement phases distribution (C2S and C3S) reveals their degree of weathering. The results obtained by CRM evidence a surprising coexistence of carbonate with amorphous carbon indicating that weathering mechanism in more complex than expected. Moreover, the size of sulphate particles contributes kinetically to weathering reaction. The weathering of cement particles by the atmospheric agents requires thus the combined action of amorphous carbon and sulphate. This study opens new analytical possibilities applied to commercial cements due to the combined chemical and spatial high resolution of CRM.This work was supported by the Spanish Ministry of Economy and Competitiveness through the Project MAT2013-48009-C4 and the Spanish National Research Council under Project NANOMIND CSIC201560E068