低カーボンフットプリントのセメントを開発 (Scientists develop alternative cement with low carbon footprint)

Eco-friendly binders are among the opportunities to reduce the approximately 8% global CO₂ emissions generated by the cement industry, with calcium-sulphoaluminate (CSA) -based cements standing as a potential low-CO₂ alternative to the world most used ordinary Portland cements (OPC). Belterra Clay (BTC), an abundant low-cost alumina-rich clay overburden on the huge bauxite reserves of the Brazilian Amazon was tested to produce CSA-based binders. Successive Designs of Experiments were used to prepare mixtures containing BTC, CaCO₃, and gypsum, seeking the maximum BTC and minimal CaCO₃ consumption under the lowest possible temperature to maximize CSA’s main phase ye’elimite, Ca₄Al₆(SO₄)O₁₂, in the clinkers. X-ray powder diffraction accompanied by Rietveld phase quantifications, X-ray fluorescence, and scanning electron microscopy were used to characterize the obtained products and guide the experimental work. CSA-belite and CSA-ternesite clinkers were successfully sintered at 1250 °C using up to 42% of BTC. The hydration of selected clinkers was investigated by isoperibolic heat flow calorimetry after blending with gypsum at 95:5 and 90:10 mass ratios. The main hydrations of the clinkers were faster (within 24 h) when using 5% of gypsum. Ettringite was the main hydrated phase, followed by kuzelite, straetlingite, and hemicarboaluminate. Produced mortars reached up to 40 Mpa after 28 days of curing, a strength development comparable to that of an OPC (46 Mpa) tested under the same conditions. BTC, currently a drawback during bauxite mining and rehabilitation of mined areas, was successfully used to produce clinkers that generate ca. 30% less CO₂ during calcination when compared to OPC, with further CO₂ and energy savings expected because of the required lower sintering temperature.