A comparative study of natural pozzolans used in blended cement production

The economic problem of energy consumption in the cement 1ndustry 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 the blendect cement. Samples of fifteen natural pozzolans used by cement factories in Turkey 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, particle size distribution ability to be ground, pozzolanic activity and chemical compositions were studied. Blended cements were prepared in the laboratory by mixing 15% of pozzolan with 85% of normal portland cement; water requirements and times of setting determined. Flexural and compressive strengths, workabilities, drying shrinkages and freezing and thawing resistance determined by cycles of immersion in magnesium sulfate and oven drying were examined on standard mortars specimens. The pozzolans used were fresh or altered pyroclastic tuffs representing rhyolite, basalt, trachyte, andesite and dacite. Some of them contain 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 can not be proposed on the basis of current data. Further systematic and detailed researches are needed.