Diatomaceous earth: a natural pozzolan of the Paraná Basin, state of São Paulo

Abstract

Prospection of pozzolanic materials in the Paraná Basin, State of Sao Paulo, identified a sedimentary rock composed essentially of siliceous spicules of sponges and of siliceous frustules, known as diatomaceous earth. Such siliceous skeletons present pozzolanic properties as they react with calcium hydroxide forming a cementitious material. We present analytical techniques for preliminary qualification and quantification of pozzolanic materials. Besides, X ray diffraction and scanning electron microscope analyses for diatomaceous earth are also examined. Selected samples composed essentially of siliceous skeletons submitted to pozzolanic reactivity tests with lime mortar gave compressive strengths at 7 days greater than 6 MPa. Although these rocks can be considered as natural pozzolans, they cannot fulfill the needs of the cement industry. On the other hand, they can be used as raw materials for manual brick fabrication, which is an important issue to stabilize rural populations.