Cimentos de baixo impacto ambiental (LC3 ) a partir dos resíduos cauliníticos da Amazônia

Abstract

The use of mineral additions as a partial replacement of clinker in Portland cement has been one of the main strategies for reducing CO2 emissions by the global cement industry. However, the availability of blast furnaces and fly ash does not meet demand. In the Amazon, the kaolin processing industries as a cover for paper have already deposited around 70 million tons of waste consisting essentially of extremely fine kaolinite. An alternative for the region would be the use of Portland cement with mineral additions of limestone and calcined clay for the production of a low CO2 cement - LC3 (limestone calcined clay cement). The objective of this work was to evaluate the properties of these LC3 cements with high incorporations of limestone and metakaolin from the kaolin processing residue. The levels of substitution of mineral additions on the common Portland cement mass were 45% and 60%. The investigated variables were specific mass, specific surface area Blaine, water of consistency and time of initial and final setting of the cement, in addition to the resistance to mortar compression. The incorporations of the metakaolin-lime mixtures increased the water demand and reduced the setting times due to the high fineness of the kaolinite. However, there were significant increases in compressive strength compared to common and compound Portland cements, demonstrating the high efficiency of this binder which reached compressive strength of up to 62.3 MPa at 91 days. As for the carbon footprint produced by LC3 cements. The results showed a 20% to 38% reduction in CO2 emissions compared to CPII F 40. Furthermore, the wide applicability of the LCA tool to the construction sector was evidenced. The results are promising, but require further studies, especially with regard to the aspects of rheology, durability in view of the high water demand of these cements, high tendency to retraction and low alkalinity and, mainly, regarding economic viability when combined with other actions to mitigate emissions such as increasing energy efficiency combined with the use of alternative fuels.