Efflorescence in calcined kaolin sludge based geopolymers

Reference	Presenter	Authors (Institution)	Abstract
04-078	Ana Paula Kirchheim	Kirchheim, A.(UFRGS); Martinez, E.D.(UFSM);	Geopolymers are a type of binder produced with a simple mixture of an aluminossilicate mineral (known as a solid precursor) and a highly alkaline (activator) solution. Despite the current development of these alternative cements, there are still many questions about its durability and one of this is related to the efflorescence formation. When looked at the precursor, there is a deep interest in evaluating the efficiency of different materials. Metakaolin (MK) is one of the main ones because of its high purity (Si/Al ? 1 ratio and low contaminant, high reactivity and homogeneity. However the pure kaolin needed is used to other industrial applications and could not be available. In the process of purification of kaolin is generated a sludge with high content of kaolinite and if well treated thermally it can present a good reactivity. After thermal process is generated a calcined kaolin sludge with high content of metakaolinite. In this sense, this work aims to evaluate the susceptibility in the development and/or formation of efflorescence in calcined kaolin sludge geopolymers produced with different activation conditions as activation concentration expressed as percentage by weight of M2O (10 and 20%) and presence of silicate soluble from sodium silicate with different SiO2/M2O modulus (MS between 0 and 1). The susceptibility to the development of efflorescence was evaluated and quantified by the visual appearance of the materials in aggressive conditions, changes in mechanical resistance, absorption and permeability to water and alkali leaching. The formation of efflorescence and alkali leaching relative to the activation factors was observed. The samples that presented lower susceptibility to carbonation and lower mechanical performance were those that presented more content M2O and MS content. This effect is attributed to crosslinking and formation of dense geopolymer matrix.
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