Using response surface analysis for the optimization of mechanical strength and microstructure of geopolymers with different SiO2/Al2O3 and SiO2/Na2O ratios

Abstract The increasing release of gases that cause the greenhouse effect brings the need to develop products that minimize the environmental impact. In the civil construction sector, clinker, the main raw material for cement, releases large amounts of carbon dioxide during production. Thus, research related to geopolymers has stood out due to the lower release of gases into the atmosphere. Geopolymers are materials developed from aluminosilicates activated in a highly alkaline medium through geopolymerization. The compositions were prepared by varying the sodium hydroxide solutions NaOH (5, 7.5, and 10, Mols/L) and the proportions of sodium silicate Na2SiO3 to NaOH (1:2, 1:1 and 2:1) to determine a composition with the best characteristics. The factorial experiments of the type 3² were planned with 2 factors and 3 levels. The materials obtained were analyzed at 7 days of curing at room temperature. With the analysis of the results, it was possible to identify that the variation of the parameters SiO2/Al2O3 and Na2O/SiO2 have a significant influence. The Na2SiO3/NaOH ratio is the most important factor in the strength gain at early age. Compressive strength varied between 4.46 and 41.14 MPa as the smallest and highest SiO2/Al2O3 ratio, respectively.