Strength characteristics of Lightweight Geopolymer and Effect of Pre Heat Curing on Geopolymerization

Abstract

In India at present there are 151 coal/lignite based power plants which produces about 300 million tons of coal ash every year. Class F type of fly ash is produce in India and due to less puzzolonic properties it cannot be utilized effectively and considered as potential waste. The settlement of embankments over soft soil deposits can be affected by the self-weight of the embankment material and overlaid stabilized soil which can be reduced by using light weight material having adequate strength. Fly ash with GGBS as an additive has been used to produce light-weight geopolymer material by using chemical foaming agent. Pre-heat curing in fly ash and slag based geopolymer is also done to observe its effect in strength properties of geopolymer.
Fly ash with GGBS% varies from 10-50% is used with NaOH solution as an alkaline activator for geopolymerization process. Pre heat curing is done in three temperatures as 45ºC, 65 ºC and 85ºC with different Pre heat curing time period for eah temperature. Foamed and unfoamed both samples were prepared in a cylindrical mould of diameter 36.5 mm and 74 mm height. For foaming aluminum powder and hydrogen peroxide is used. Aluminum powder is added in different composition as 0.01, 0.02, 0.03, 0.04, 0.05 and 0.06 percentages and Hydrogen peroxide added as 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 percentages in a distinct moulds. A fixed percentage of surfactant (Triton X 100) is mixed with Al powder and H₂O₂ to stabilize pores. Prepared samples were given pre-heat curing of 85⁰ C for 6 hours and then cured at room temperature for 7 days before testing. Flowability and seting time test is done for the paste. Unconfined compression test was conducted to evaluate mechanical properties, while X-ray diffraction test and scanning electron microscopy (SEM-EDS) test toinspect geopolymerization reactions, composition and microstructure of the end products. It is observed that gain in strength in case of Aluminum powder is low as compared to peroxide, more stable pores were formed in case of H₂O₂ compared to Al powder as chemical. Lowest density of 0.97 g/cc is obtained by 0.5% H₂O₂ with 1.33 MPa unconfined compressive strength. CBR tests results shows the compatibility of material as lightweight subbase and subgrade for embankment construction over soft soil deposits.