Development of a complementary precursor based on flue gas desulfurization (FGD) for geopolymeric pastes produced with metakaolin

Abstract

Portland cement production is related to environmental problems and corresponds to about 6–8% of CO2 emission. Thus, it is necessary to search for sustainable material. Among these materials are geopolymers. The objective of this research was to analyze the potential of producing a geopolymeric paste based on metakaolin (MK) and Flue Gas Desulfurization (FGD) residue. First, the specimens were prepared with a curing time of 7 days in two types, one ambient and the other thermal at 65 °C. After that time, tests were carried out in the hardened state of compressive strength, bulk density, water absorption and void ratio. Tests were also carried out with the mixture in the fresh state, through tests of consistency index, mass density and incorporated air, water retention and calorimetry. Finally, the characterization of the samples was carried out through X-ray diffraction (XRD) and scanning electron microscopy (SEM). The compressive strength results showed that the best compositions were 100% MK (0%FGD) and 95% MK (5% FGD) residue with thermal cure at 65 °C. The values found were 47.65 MPa and 28.44 MPa, higher than the values of the main structural standards. These results were attributed to the formation of sodalite and faujasite phases in the compositions of 100% MK and 5% of FGD residue and the non-formation of ettringite, as happened with the other two compositions. Thus, the geopolymeric pastes showed compressive strength values for reinforcement of structures with the use of MK as a precursor and its replacement of 5% by the FGD.