Properties of Fly Ash-based Geopolymer Mortar: Influence of Fly Ash Sources and Sodium Silicate (Na2SiO3) / Sodium Hydroxide (NaOH) Ratios

Abstract

Abstract

This paper presents the properties of fly ash-based geopolymer mortar (FGM). Two sources of fly ash obtaining from Mae-moh fly ash in Lampang province and Rayong fly ash in Rayong province were used. In addition, the activate alkali solution ratios of sodium silicate (Na2SiO3) / sodium hydroxide (NaOH) were studied. The fresh state properties of FGM included flowability, setting times and temperature rise during subjecting to three curing methods--(a) water at room temperature, (b) continuous curing in electric oven at temperature levels of 40°C, 60°C and 80°C for 24 hours, and (c) microwave energy at an operating frequency of 2.45 ± 0.05 GHz with magnetron powers of 100, 300 and 450 watt for 5, 15 and 30 minutes, respectively. The properties to be studied after curing were compressive strength, microstructural characteristics, change in heating energy and temperature, group function and porosity.  The test results indicated that the water requirement of FGM was increased as increased of Na2SiO3/NaOH ratio, while setting times were conversely decreased. When curing the FGM prepared by Rayong fly ash with a Na2SiO3/NaOH ratio of 2.5 using electric oven at 60°C, the highest compressive strength of mortar was obtained. Further FGM prepared by Mae-moh fly ash with a Na2SiO3/NaOH ratio equal to 1.5 by water curing gained the highest one. Curing by microwave energy at 450 watt gained the highest compressive strength of FGM containing Mae-moh fly ash with a Na2SiO3/NaOH ratio of 2.5. From microstructural test, it was found that the Si-O-Si functional groups were formed in all FGM samples from geopolymerization process resulting in forming structure that developed compressive strength. Whereas FGM structures have low weight change and low energy level. Finally, from the pore size analysis, it indicated that FGM containing Mae-moh fly ash curing by oven has higher uniformity in pore size than that of FGM containing Rayong fly ash, and has the smallest pore volume when compared to FGM under other curing methods.

Keywords : Curing; Fly ash; Geopolymer mortar; Microwave energy