The Use of Natural Pozzolan in Concrete as an Additive or Substitute for Cement

Abstract

Abstract : Chemical, physical, and mechanical tests were conducted to assess the feasibility of using naturally occurring pozzolan as a ce-ment mortar additive. One test series assessed the feasibility of substituting pozzolan for a portion of cement in concrete mortar mixtures. The chemical composition of five natural pozzolans was determined. Compressive testing was conducted on specimens with varying amounts and types of pozzolan. One pozzolan was found suitable for cement replacement in Type M mortars, and one was suitable for cement replacement in Type N mortars at a different proportion. The results indicate that, within certain mixture percentage limits, partial replacement of cement with pozzolan does not compromise mortar compressive strength. A second test series evaluated four mixes prepared using three types of natural pozzolan as well as Class F fly ash. The effective-ness of each cement replacement material in controlling alkali-silica reactions was studied. Correlations were made between the mechanical properties of the proposed mixes and a Portland cement control mix. The results were also compared with industry standards for mortars made with fly ash and silica fume. Results indicate that one type of pozzolan may be used as a substitute for fly ash, but not for silica fume.