EVALUATION OF BLENDED PORTLAND - POZZOLAN CEMENTS CONTANING DIATOMACEOUS EARTH

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Abstract
04-054 PEDRO CESAR RODRIGUES ALVES ABRAO ABRAO, P.R.(Escola Politécnica - Universidade de São Paulo); Cardoso, F.A.(Escola Politécnica - Universidade de São Paulo); John, V.M.(Escola Politécnica - Universidade de São Paulo); One of the strategies to reduce the CO2 emissions of cement industry is the replacement of clinker by supplementary cementitious materials. Among these materials the pozzolans are highlighted by being present in large volume in the Earth's crust. Diatomite is a material that is formed from accumulation of algae shells that were fossilized due to silica deposit on its structure, and its occurrence  is associated with clay and quartz, then composing the diatomaceous earth. The objective of this study is to evaluate the reactivity, as well as water and superplasticizer demands of Brazilian commercials cements containing diatomaceous earth. Two cements with 13% (CPII-DE) and 45% of diatomaceous earth (CPIV-DE) were analyzed and compared to a high-early strength cement (CPV). All cements were physically and chemically characterized, and the superplasticizer saturation content was determined by rotational rheometry of the pastes, while the water demand for mortars was defined through the Flow table. After curing the pastes and mortars for 7, 28 and 91 days, the combined water was quantified by thermogravimetry, which supported the calculation of capillary porosity and hydrates volume; plus, the compressive mechanical strength of the mortars was assessed according to EN196-1.  The CPIV-DE, obtained the highest additive saturation content, due to its high surface area. The mortars prepared with the pozzolanic cements, requested a smaller volume of water to reach the spreading of 240mm on the flow table. For all curing times the pozzolan cements had a smaller volume of chemically combined water, due to their lower clinker content, reducing the volume of hydrates, increasing porosity and, consequently, reducing mechanical resistance. Finally, the environmental indicators, CO2 intensity and energy intensity, indicated that the dilution of the clinker by diatomaceous earth only compensate for high replacement content (CPIV-DE).
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