Effect of Silica and Lignocellulosic Material as Additives on the Kinetic of Geopolymerization through ATR-FTIR Spectroscopy

Abstract

This study compares the effect of the addition of sawdust (S), rice husk ash (RHA) and fired sand (Sa) on reaction kinetics, mechanical properties and microstructures of geopolymers for filtering application. Two kaolins were used as aluminosilicate sources. The kinetics of the formation of the Si-O-Al bond of eight final compositions were performed through in-situ FTIR spectroscopy; then their mechanical properties and microstructures were also achieved. It was found that the addition of around 1 wt% of S, 5 wt% of RHA and 10 wt% of Sa was suitable to obtain geopolymer networks within the range of geopolymer zone in Metakaolin-Silica-Alkaline solution (M-S-A) ternary diagrams. ATR-FTIR spectra shows that the Si-O-Si/Al bond shifts between 9 and 19 cm-1 with a slope between -0.06 to -0.02 cm-1/min. It was found that the addition of sawdust slightly decreases the reaction rate than silica additives (rice husk ash and fired sand). The compressive strength of MK2-based geopolymers was higher (90 and 130 MPa) than that of MK1-based geopolymers (57 to 80 MPa) even though the addition of sawdust decreased the mechanical properties of specimens than silica (RHA and Sa). From the point of view of microstructure, nanometric to micrometric networks were observed into the designed geopolymers. MK2-based geopolymers were more compact than MK1 and the porosity appeared on the matrix with sawdust which reduced simultaneously the density of specimens. The elaborated materials were lightweight with good mechanical performance, properties required in various field as filter designing.