Production and Use of Calcined Natural Pozzolans in Concrete

The aim of producing concrete providing long-term durability with regard to properties such as improved sulfate resistance and reduced susceptibility to alkali-silica reactions (ASR) has led to development of several high-performance materials. While use of fly ash and ground granulated blast-furnace slags in concrete has gained acceptance in some applications, the mineralogical composition of such byproduct materals cannot be controlled as easily as a manufactured pozzolan. Processing of performance enhancing pozzolans is accomplished by thermally treating and converting crystalline clay materials to amorphous alumino silicates. These pozzolans can be interground with portland cement clinker and gypsum to produce a Type-IP blended cement, or ground separately as mineral admixtures for concrete. This paper describes some of the choices available to manufacturers of blended cement to engineer into the cementitious system desired properties for concrete such as improved sulfate resistance, reduced permeability, and the ability to strongly mitigate ASR.