Resistance of fly ash based geopolymer mortar to both chemicals and high thermal cycles simultaneously

Abstract

Geopolymer has already been used at a commercial airport, Brisbane West Wellcamp Airport (BWWA), and in mainline railway sleepers in Australia. It has also been proposed for use at military airbases to repair degraded concrete or any other special construction needs. Rigid pavements at military airbases, especially aprons, are frequently exposed to high thermal shocks by jet exhaust, and often get saturated by chemicals such as hydrocarbon fluids (HFs): aircraft’s engine lubricating oil, hydraulic fluid and jet fuel. To promote wider and reliable use of geopolymer at military airbases, the resistance of geopolymer to both HFs and high thermal cycles should be thoroughly assessed. The present study investigates the resistance of fly ash (FA) based 3-day and 28-day old geopolymer mortars to both HFs and high thermal cycles simultaneously and separately. This study has identified that irrespective of the age of the geopolymer mortar, they experience saponification when expose to both HFs and high thermal cycles simultaneously. Soap and salt compounds, e.g., sodium carboxylate and sodium phosphates were identified in the geopolymer mortar after the saponification occurrence. The crystal lattices of the 3-day old geopolymer mortar were significantly affected and decomposed when exposed to HFs and high thermal cycles simultaneously. Upon 60 cycles of heat exposure, 3-day and 28-day old geopolymer mortar treated with HFs lost 42.52% and 33.85% of their compressive strength, respectively. The geopolymer mortar exposed to HFs at ambient temperature did not suffer from saponification process, and the reduction in the compressive strength was almost insignificant. The effect of high thermal cycles in reducing the compressive strength of the geopolymer mortar was substantial. This paper also reports mass loss characteristics, microstructures and degrading mechanisms of geopolymer mortar after exposure to HFs and high thermal cycles.