INTERFACIAL TRANSITION ZONE BETWEEN AGGREGATE AND PASTE IN CEMENTITIOUS COMPOSITES (II): MECHANISM OF FORMATION AND DEGRADATION OF INTERFACIAL TRANSITION ZONE MICROSTRUCTURE,AND ITS INFLUENCE FACTORS

Abstract

The microstructure models of interfacial transition zone( ITZ) were represented. The mechanism of formation and degradation of ITZ's microstructure was described by three stages. They involve: (1) the fresh stage of concrete and the early period of hy-dration, (2) the hardened period and (3) the service period of materials. At the first stage, the mechanism is possibly due to a wall effect, flocculation of binder, microbleeding effect, transportation, precipitation and nucleation of ion, one-sided growth of hydrated products and syneresis. At the second stage, chemical shrinkage, self-desiccation shrinkage, drying shrinkage, the difference in expansion coefficient between aggregate and paste, hydration of paste and re-crystallization of hydrated products can be contributed to the mechanism. At the last stage, the mechanism is attributed to the load, aggressive agent, freeze-thaw, alkali-aggregate reaction and continuous hydration of paste. In this review, the conventional characteristic methods of ITZ's microstructure were briefly described. The new characteristic method and two alternative approaches were shown. In addition, the influence of physical and chemical characteristics of raw materials, mixture design and processing on the microstructure of ITZ were reviewed.