Geopolymerization of fly ash: effect of sodium and potassium
摘要
Research has been generated around the development of geopolymers to replace Portland cement in the construction industry, which would be a very promising solution for the building. Geopolymers are alkaline-activated inorganic materials, with potential use as industrial by-products, offering environmental and economic gains. While cement production contributes to environmental problems such as CO2 emissions, geopolymers promise to reduce these impacts. Fly ash, a by-product of thermoelectric plants, is highlighted as a viable and low-cost raw material for geopolymers, with high global availability. The study proposes the use of this ash in the production of geopolymer mortar, analyzing molarity variations with the use of commercial sodium hydroxide and potassium hydroxide, main activators used in geopolymers. In the study, results showed that fly ash is rich in aluminosilicates and has fine grain size, which contributes to obtaining good properties in geopolymers. Tests indicated an increase in mechanical strength with increasing molarity, both for geopolymers activated with sodium (5 M to 7 M increase 25 MPa to 35 MPa) and for those activated with potassium (5 M to 7 M increase 2 MPa to 5 MPa). Superior mechanical strength results were found in samples manufactured with sodium hydroxide, with values 5 times higher in the 28-day test, as well as greater density (1.88 g/cm3 and 1.67 g/cm3), more homogeneous microstructure and less porous, indicating effective geopolymerization. The results are contrary to other research that highlights that the use of potassium favors strength, as it is more alkaline. However, it is concluded that this issue varies depending on the type of precursor, alkalinity of the solution and type of methodology applied in the production of the material.