Influência da geopolimerização no controle dos efeitos deletérios da reação álcali- gregado (RAA) em argamassas de cimento Portland e agregados naturais da Região dos Campos Gerais no estado do Paraná

Abstract

The alkali-aggregate reaction (AAR) is a pathological manifestation that can cause severe damage to Portland cement composites. Certain alkali-activated cements and geopolymers show similar mechanisms to AAR, especially at the beginning of the dissolution reactions of aluminates and silicates in an alkaline environment. The objective of this study is to test alkali-activated materials based on metakaolin, sodium hydroxide and sodium silicate to control the occurrence of AAR in Portland cement mortars by controlled replacement of conventional cement with geopolymers. For this study, seven different aggregates were collected from the region of Campos Gerais, State of Paraná, showing a wide range of reactivity, with the majority showing at least potential reactivity with Portland cement alkalis. In the formulation of geopolymers, it has been observed that factors such as temperature, the ratio of activators to precursors, and the molarity of the activator solutions have a direct influence on the mechanical strength, porosity, and crystallinity of the materials. Although geopolymers are predominantly amorphous materials, the formation of sodalite and zeolite crystals was observed in the porous matrix of these products, and the expansions caused by AAR were not observed in the geopolymer mortars. Mortars were prepared with Portland cement replaced by metakaolin in proportions of 5, 10, 15 and 20%, cured in water as well as in NaOH solutions kept at 60 oC. In addition, mortars were prepared with Portland cement replaced by geopolymers in the same proportions, but cured in water at 60 oC. Through accelerated AAR tests on mortar bars, SEM with EDS, XRD and FTIR, it was concluded that geopolymers can be formed in the matrix of mortars composed of Portland cement, provided that favorable conditions are met, promoting the formation of dense and non-reactive products to the detriment of AAR gels. The formation of amorphous geopolymers in Portland cement mortars has a positive influence on mechanical strength, reducing absorption and expansion caused by AAR.