Transport Properties of Pozzolanic Concrete Based on the South African Durability Indexes

Abstract

Engineers and designers often incorporate pozzolans in concrete to enhance specific properties, most notably, its resistance to ionic penetration that directly depends on the cover concrete’s transport properties, which are a function of the microstructure. This paper describes the influence of pozzolans on concrete microstructure and durability-related transport properties measured according to the South African durability indexes. The resistance of pozzolanic concrete to oxygen permeation, water absorption and chloride diffusion was evaluated. The pozzolanic materials considered were fly ash, blast-furnace slag, silica fume and metakaolin. These materials were used as partial replacement for the Portland cement in binary mixes. At the ages tested, the metakaolin mix displayed excellent performance in strength development, microstructure enhancement and durability. The results also show that the mixture incorporating metakaolin exhibited the highest resistance to oxygen permeation, chloride conduction, and the lowest porosity, followed by the blastfurnace slag mix. The silica fume mix displayed the highest resistance to water absorption, while the fly ash mix exhibited the most moderate resistance to water absorption and chloride conduction.