Fly ash red mud geopolymer with improved mechanical strength

Abstract

World produces annually multimillion of tones of fly ash (FA) and red mud (RM) as industrial wastes. There is a dire need to develop a process that can potentially use these wastes as large stockpiling of these materials can lead a potential hazard to the common people. The FA is rich in silica and alumina, two major ingredients of the aluminosilicate network containing inorganic polymer called geopolymer. The present work demonstrates the geopolymer prepared from fly ash and red mud (FA-RM-geopolymer) with significant high strength of 65 MPa under optimized experimental conditions. Geopolymers were synthesized from the raw material under ambient condition of 25 °C with 28 day of curing. It was observed that after 28 days of curing maximum compressive strength of 65 MPa was achieved in presence of 10 wt percent of red mud. While fly ash based geopolymer (FA-geopolymer) showed 53 MPa compressive strength under similar experimental conditions. X-ray photoelectron spectroscopy (XPS), X-ray diffraction spectroscopy (XRD), particle size analysis and FE-SEM were used to study the structural properties of raw material and the geopolymer. XPS studies revealed that the iron of the RM does not take part in the geopolymerization, as no change was observed for the Fe2p 3/2 peak of the RM and FA-RM-geopolymer. However significant change was observed for the Al2p 3/2 XPS peak. Further it was observed that the presence of RM resulted in increases Si/Al and Na/Al molar ratio compared to FA-geopolymer. SEM studies confirmed the formation of high dense structure for the FA-RM-geopolymer suggesting RM provides aluminum to participate in the geopolymerization and simultaneously acts as filler thereby leads to enhanced and active geopolymerization process on blending of fly ash with red mud. • Fly ash with red mud geopolymer has been studied by XPS, XRD and SEM. • Presence of 10 wt % red mud results in high compressive strength. • XPS studies revealed increase in Si/Al and Na/Al molar ratio in presence of red mud. • Red mud leads to enhanced geopolymerization process.