2019 CSCE Annual Conference - Laval (Greater Montreal) Conference
Dr. Hocine Siad
Mr. Mohamed Lachemi,
Mr. Obaid Mahmoodi
Dr. Mustafa Sahmaran
The production of geopolymers comprises an intricate chemical reaction between a solid aluminosilicate source and an alkali hydroxide or a silicate solution, which may result in an amorphous alkali-aluminosilicate product. Supplementary cementitious materials (SCMs) such as Metakaolin (MK) and Fly ash (FA) are well-recognized materials as rich sources of silica and alumina contents. However, the geopolymeric network demands higher soluble content of silica as well as alkaline ions such as sodium (Na+) and potassium (K+). Variations in these soluble contents affect four primary chemical ratios in geopolymerization process: SiO2/Al2O3, R2O/SiO2, R2O/Al2O3 and liquid/solid, in which R is Na+ or K+. Consequently, the dissolution and coagulation of Si and Al from the source materials in alkali solution affect the rheological properties of fresh geopolymer paste. This study aimed to investigate the rheological characteristics of a geopolymer network composed of metakaolin, fly ash type F (FAF) and fly ash type C (FAC) as precursors, and sodium silicate and sodium hydroxide as alkaline reagents. The mix design technique used in this study was developed based on constant liquid/solid ratio and five different levels of SiO2/Al2O3 and Na2O/SiO2. The rheological parameters of the fresh pastes were correlated with the chemical factors considered in the mix design procedure. The results show that the increasing in SiO2/Al2O3 decreased yield stress and viscosity of the geopolymer mixes derived from MK and FAF. On the other hand, increasing in Na2O/SiO2 performed oppositely and decreased shear stress of material. Geopolymer paste mixtures containing fly ash type C exhibited entirely different due to the higher reactivity and faster dissolution of calcium contents in the material.