Influence of the nature and concentration of alkali cations in silicate solutions on the behavior of MK-CaCO3 based geopolymers at 600–1150 °C

The objective of this work is to study the effect of the nature (potassium or a mixture of potassium and sodium) and concentration of alkali cations on the behavior of geopolymers at a high temperature (1150 °C). First, the physico-chemical characteristics of the different geopolymers, such as the initial viscosity, the density of the mixture and structural data (Raman spectroscopy), are presented. Then, thermal analysis, dilatometry and mercury porosity are conducted, as well as the mechanical behavior and X-ray diffraction after 1150 °C. The different formulations display different trends depending on the concentration and the nature of the alkaline cations. In comparison to the use of a potassium cation, the addition of sodium leads to an increase of the viscosity and a decrease of the onset temperature of the viscous flow. The potassium-based formulations show better behavior after treatment at high temperature (1150 °C). The improvement in the mechanical properties after thermal treatment is controlled by the different crystalline phases formed, such as leucite and anorthite.