Microstructure properties

Abstract

Concrete comprises of three different phases such as (1) aggregate, (2) hardened cement matrix and (3) interfacial transition zone (ITZ) between the aggregate and matrix. Heterogeneity in concrete at the microstructural level is caused mainly due to the non-uniform distribution of water in the zone near an aggregate edge and that farther from the aggregate that is in the matrix region. Phenomena which occur closer to an aggregate surface in concrete are: (1) availability of more water which facilitates formation of larger size capillary voids after hydration (2) growth of preferentially oriented layer of crystalline hydrated products (mainly calcium hydroxide) and (3) development of microcracks even prior to loading. Moreover, the microstructure rather than being fundamentally constant, varies with curing ages. Presence of aggregates in general (due to wall effect) and types of aggregate such as recycled coarse aggregate in particular result in a complicated and inhomogeneous microstructure than the plain cement paste. The layer of adhered mortar on the surface of recycled coarse aggregate makes the interface more complex. In this chapter, we will try to find out answer to the following questions: How does incorporation of supplementary cementitious materials alter the aggregate-matrix interface in recycled aggregate concrete? How do the microstructural properties affect the macro behaviour of concrete?