Estudo de ligante geopolimérico obtido a partir de metacaulim e escória granulada de alto forno

Abstract

The need for alternative materials to replace Portland cement is a contemporary discussion. Those new and alternative materials must have a sustainable character and good durability to supply the demand of the civil construction sector and mitigate the environmental crises caused by the industry, such as the high emission rate of CO2. In this context, geopolymeric binders appear as materials produced by different solid precursors in contact with an alkaline activator, with zero CO2 emission and mechanical properties and durability compatible or superior to that of Portland cement. Thus, this study aimed to evaluate the geopolymeric binder obtained from the combination of metakaolin (MK) and ground granulated blast furnace slag (GGBFS) with three different molar concentrations of sodium hydroxide (8, 10, and 12 M) for the alkaline activator. Dosages were established from the partial mass substitution of MK by GGBFS, coded as G0 (100% MK 0% EAF), G20 (80% MK 20% EAF), and G40 (60% MK 40% EAF). XRD, XRF, and SEM analyses were conducted for solid precursors. Geopolymer pastes properties were evaluated in the fresh state regarding setting time and in the hardened state based on physical tests, average compressive strength, and fracture morphology. Results showed that the MK and the GGBFS have adequate reactivity and chemical composition for the geopolymer synthesis, with the presence of calcium in the GGBFS actively contributing to the reduction of the setting time and gain of mechanical resistance of the dosages. As for the hardened state, higher levels of water absorption are intrinsically related to a decrease in mechanical strength, with fracture analysis revealing the presence of pores and micropores that favor the propagation of cracks. Statistical analysis found that the interaction between the analyzed factors significantly influenced the properties of the materials, with 85.35% (R2 = 0.8535) of the model being able to explain the variation in compressive strength of geopolymers as a function of the factors used in the regression, limited to the chosen range of variables. The G40M12 formulation showed the highest compressive strength value (38.08 MPa) and the ideal synthesis parameters defined were the rotational frequency at 150 RPM, a partial replacement of MK by GGBFS of 40%, and the NaOH concentration of 12 M. Finally, from the correlation of the evaluated characteristics, the developed geopolymeric binders showed technological potential as alternative and sustainable materials, with properties comparable to those of Portland cement.