Microstructure of concretes containing artificial and recycled aggregates

Abstract

The microstructure of concrete specimens containing various artificial aggregates have been characterized by means of polarizing and fluorescent microscopy (PFM) and scanning electron microscopy (SEM). The artificial aggregates in question were Lytag, Aardelite, Liapor, incinerator-source slag, recycled masonry and recycled concrete. The concrete specimens examined had prior to this study been subjected to carbonation tests for various periods of time ranging from 2 to 5 years. Of specific importance to the study were the pattern of carbonation in the concrete specimens, the capillary porosity and homogeneity of the cement paste, the intensity and distribution of microcracks, and the characteristics of the cement paste-aggregate interfacial zone. Results of the fluorescent thin section analyses revealed that the use of specific sizes of certain types of these artificial aggregates tend to influence the pattern of carbonation of the concrete. With the exception of a few distinct features associated with the concretes studied, their microstructural characteristics are in general comparable with concretes containing conventional natural aggregates. These distinct features and characteristics have been presented in this article with photomicrographic illustrations.