Characterization and properties of bamboo ash replacement in fly ash based geopolymer concrete

Abstract

Malaysia, as a tropical rainforest country, enjoys an abundance of bamboo plant that proliferate throughout the country. The application of geopolymer technology has become a trend and preserves the environment from harm. Fly ash geopolymer concrete has low early strength and requires 24 hours for the concrete to harden. Thus, the presence of calcium and potassium content in bamboo ash could remedy this problem. Besides, there is no research regarding the use of bamboo ash as a binder in geopolymer concrete. Therefore, the presence of bamboo ash could improve the research field with the use of agriculture waste in a building construction. The research aim is to use bamboo ash in the production of fly ash geopolymer concrete. The specimens were casted in 100mm x 100mm x 100mm cubes and sodium based activator were used as the alkaline solutions. The binders are formulated with different binder ratio and solution to binder ratio. All test specimens were cured at ambient temperature (23°C -25°C) and 100% fly ash was chosen as control specimen. For fresh state properties, 3 tests were conducted, which are setting time, flow table and geopolymerization test. For hardened state properties, 10 different experiments were tested which are compressive strength, flexural strength, splitting tensile strength, modulus of elasticity, ultrasonic pulse velocity, water absorption, density, drying shrinkage, thermal expansion and elevated temperature. Lastly, phase analysis and microstructure analysis were conducted for 7 days and 28 days of curing age. The test results depicted that as the percentage of bamboo ash decreases, compressive strength increases. Also, the addition of 5% of bamboo ash into fly ash geopolymer concrete could improve the early strength in 7 days. The results were proven with the phase analysis that explains the effectiveness of the formation of sodium aluminate silicate hydrate (NASH) and calcium aluminate silicate hydrate (CASH) for the strength of geopolymer matrix. Furthermore, addition of 5% of bamboo ash reduced the setting time of fly ash geopolymer concrete by 40%. The addition of bamboo ash improved tensile strength and also compressive strength when exposed to elevated temperature of 800°C. Therefore, it can be concluded that the addition of bamboo ash improved the early strength, setting time, tensile strength and compressive strength when exposed to high temperature.