Comparative Study of Natural Pozzolans Used in Blended Cement Production

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Title: Comparative Study of Natural Pozzolans Used in Blended Cement Production

Author(s): M. S. Akman, F. Mazlum, and F. Esenli

Publication: Special Publication

Volume: 132

Issue:

Appears on pages(s): 471-494

Keywords: blended cements; durability; freeze-thaw durability; mineralogical analysis; petrography; pozzolans; setting (hardening); strength; workability; Materials Research

Date: 5/1/1992

Abstract:
The economic problem of energy consumption in the cement industry obliges many countries to produce blended portland pozzolan cements. These pozzolans have different origins and mineralogical structures influencing the qualities of the concrete. The criterion of mechanical strength of standard cement mortars is generally judged sufficient for marketing theblended cement. Samples of 15 natural pozzolans used by cement factories inTurkey were investigated in this research. Petrographic and mineralogical characteristics were determined by microscopic and x-ray diffraction examination. Their properties--including density, water absorption, specific surface; article size distribution, ability to be ground, pozzolanic activity, and chemical compositions--were studied. Blended cements were prepared in the laboratory by mixing 15 percent of pozzolan with 85 percent of normal portland cement; water requirements and times of setting were determined. Flexural and compressive strengths, workabilities, drying shrinkages, and freeze-thaw resistance, determined by cycles of immersion in magnesium sulfate and oven drying were examined on standard mortar specimens. The pozzolans used were fresh or altered pyroclastic tuffs representing rhyolite, basalt, trachyte, andesite, and dacite. Some of them contained phenocrysts, clay minerals, zeolites, and calcium carbonates. They exhibited different properties as powders, in pastes, and in mortars. Reliable and distinct relations between petrographic types and engineering properties cannot be proposed on the basis of current data. Further systematic and detailed research is needed.