Role and Regulation of the Transition Zone in Realizing High Performance Concrete

The transition zone which is formed at the interface between cement paste and aggregate affects decisively the properties of hardened concrete. The transition zone in ordinary concrete consists mainly of a highly porous three dimensional network structure of calcium hydroxide crystals with pores from 50 nm to 2 micrometers in diameter. Its thickness is usually 30 to 40 micrometers. The structure of the transition zone is closely related to the conditions of concrete manufacturing, including composition and structure of materials, proportions and curing conditions. The effects on concrete properties by the formation of the transition zone and the measure to reduce the formation of the transition zone, which causes the deterioration of concrete quality, are also described.