Abstract
The current study focused on the utilization of local clay for synthesis and characterization of meta-kaolin based geopolymers with and without nano-silica. The control geopolymers, for a compressive strength of 30 MPa, were optimized by using Liquid/Solid ratio of 0.55, NaOH concentration of 10 M and curing at 80°C. The nano silica was added in an extended range of 1%, 2%, 3%, 5%, 7% and 10%. The synthesized nano-silica metakaolin based geopolymers was investigated by using compressive strength, XRD, XRF, FTIR, SEM, MIP, TG, UV/VIS spectroscopy, in addition to density, water absorption and initial setting times. The results indicated an increase in the compressive strength value with the incorporation of nano-silica in geopolymer mixes until the optimum percentage of 5%, while the 10% addition of nano-silica decreased the compressive strength by 5% as compared to the control geopolymer. The increase in the compressive strength was accredited to the increase in the content of N-A-S-H gel and the amorphous structure as shown by XRD and FTIR analysis. In addition, the optical transmittance analysis, MIP and SEM scans along with the results of density and water absorption have clearly shown the densification of the matrix formed for the optimal percentage of nano-silica. However, the initial setting time was found to reduce substantially with increase of nano-silica content. Moreover, the TG results have shown the 5% nano-added geopolymers to have greater thermal stability as compared to reference geopolymers. Finally, the adopted methodology in this research has shown that 5% nano-silica, is the optimal result for the synthesis and the production of local meta kaolin based geopolymer, with regard to the improvement of physical properties, micro structure and compressive strength.
Highlights
Geopolymers, in the last few decades, have shown a significant potential to be used as a cementitious material
This reduction is attributed to the acceleration of the chemical reaction at early ages which is related to the easy connection between the unsaturated Si-O and Si bonds of nano-silica atom located in the surface and the free ions of Metakaolin
The current study was done to optimize the synthesis of geoplomyer with and without incorporation of nano-silica using a local metakaolin as an aluminosilicate source
Summary
Geopolymers, in the last few decades, have shown a significant potential to be used as a cementitious material. The properties of the synthesized geopolymer depend significantly on the synthesis parameters: solvent type, source materials, mixing proportions and curing conditions [2] [3] [4] [5]. The amorphous structure and the high specific surface of nano-silica are expected to produce denser geopolymer than those with traditional additives Due to their size, nanoparticles can be dispersed in the alkaline solution, generating a large number of nucleation sites and resulting in a more homogeneous and dense network. While most of the cited works agreed that the addition of nano-silica particles generally improved the properties of synthesized geopolymers, the optimized percentage of nano-silica differed due to various experimental factors i.e. the method of dispersion of nano-silica, source of local meta-kaolin, the liquid/solid ratio, and the molarity of alkaline solution along with curing temperature. The Mercury Intrusion Porosimetry (MIP) and Thermogravimetry (TG) analysis was done for the control and optimized nano-silica geopolymer
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