Structural and Physico-mechanical Investigations of New Acidic Geopolymers Based on Natural Moroccan Pozzolan: A Parametric Study

Acidic geopolymers based on metakaolin are very promising materials but the cost and pre-treatment of kaolinic clays minimize their economic and ecological properties. The search for natural geo-resources that can be used in their natural state has become a necessity. The objective of this work is to develop acidic geopolymers based on natural pozzolan which corresponds to a pyroclastic volcanic rock abundant in nature. Natural pozzolan and phosphoric acid were mixed while varying the Si/P and H2O/H3PO4 molar ratios resulting in 20 formulations. The results found showed that the maximum physical-mechanical properties are achieved at a Si/P molar ratio equal to 1.25 and an H2O/H3PO4 molar ratio of 1.5. The microstructural characterization revealed that the attack of the natural pozzolan by phosphoric acid under optimal conditions leads to the dissolution of the amorphous phase and some crystalline phases contained in the pozzolan and the formation of an amorphous gel composed of a Si-O-P bond, which results in the obtaining of a geopolymer with interesting mechanical characteristics.