Petrographic Diagnosis of Alkali-Aggregate Reaction in Concrete Based on Quantitative EPMA Analysis

Thin-section petrography, coupled with quantitative electron-probe microanalysis (EPMA), is very useful in identifying reactive constituents and alkali-aggregate reaction in concretes, as well as in characterizing the nature of cement constituents, reaction products and gel products in old deteriorated concretes. EPMA analysis made it possible to detect chemical compositions of the unhydrated cement phases alite, belite, tricalcium aluminate, and the ferrite phase in the original cement used in old structures from Canada and Japan, made even 100 years ago. Coupled with detailed petrography in thin section, this technique also enabled us to estimate the thermal histories and composition of cement clinkers in hardened concretes, variations of CSH gels which reflect the degree of cement hydration, leaching and weathering of concretes, as well as the process of migration and alteration of ASR gels in concretes. The results thus obtained can be used for the assessment of cement properties and the durability of old concretes.