NATURAL ZEOLITES AS POZZOLAN FOR REDUCING ASR OF CONCRETE

Natural zeolite can be utilized not only as a pozzolan but also as a microfiller in the concrete for the overall densification of microstructure. The pozzolanic reaction of zeolite showed reduction in calcium hydroxide component of portland cement hydration in the neat zeolite-blended cement pastes are measured at varying levels of zeolite additions. Results show a clear decrease in calcium hydroxide contents in zeolitecement pastes and greater reduction of calcium hydroxide in pastes having higher amounts of zeolite incorporations, indicating a higher degree of pozzolanic reaction. Incorporation of zeolite causes the following important microstructural modifications, which are responsible for the overall improved durability of concrete: (a) a decrease in calcium hydroxide component of portland cement hydration in the paste by the pozzolanic reaction, (b) densification of the cement paste microstructure by combined pore-size and grainsize refinements, which cause an increased volume of very fine pores at the expense of the large pores, and (c) improvement of aggregate-paste interfacial zone by a combination of filler effects and pozzolanic reaction effects. Zeolite incorporation showed a significant reduction in the potential for Alkali-Silica Reaction (ASR) expansion in our test where the paste contained highly reactive borosilicate glass as aggregates. It is indeed this alkali-binding capacity of the zeolite-cement paste along with the overall densification of microstructure, which have contributed to this reduction in alkali aggregate expansions.