Thermal, mechanical and microstructural properties of acidic geopolymer based on moroccan kaolinitic clay

The main objective of this research is the development and characterization of an acidic geopolymer based on local raw materials, namely Moroccan kaolinitic clay with phosphoric acid coming from the Moroccan phosphate industry. The influence of the calcination temperature and the liquid/solid ratio (L/S) on the mechanical and microstructural properties was evaluated. The thermal behavior of the optimized formulation was studied using FTIR, XRD, SEM, TGA/DTA, and compressive strength tests. The findings shows that highest value of the compressive strength presented by the elaborated geopolymer was about 67 MPa, which prepared by kaolin calcined at 900 °C with a ratio of L/S = 1. In addition the increase in L/S ration led to a significant decrease in the mechanical strength. The thermal behavior assessment of the optimized geopolymer reveals that these materials exhibit excellent mechanical properties even when exposed to a very high temperature of 1100 °C with a compressive strength of 13 MPa. Microstructural analysis of the thermally treated geopolymer indicates its crystallization start at a temperatures above 500 °C with the appearance of new crystalline phases stable at elevated temperatures, notably phosphocristobalite and cristobalite. The outcomes indicate that the use of Moroccan clay in the synthesis of acid geopolymers leads to excellent results with adequate calcination temperature and L/S ratio.