Document Type

Concrete and geopolymer materials paper

Publication details

Zhang, ZH, Yang, T & Wang, H 2014, 'The effect of efflorescence on the mechanical properties of fly ash-based geopolymer binders', in ST Smith (ed.), 23rd Australasian Conference on the Mechanics of Structures and Materials (ACMSM23), vol. I, Byron Bay, NSW, 9-12 December, Southern Cross University, Lismore, NSW, pp. 107-112. ISBN: 9780994152008.

Peer Reviewed



In this study, six typical geopolymer binders were synthesised using three different fly ashes (from Gladstone, Callide and Millmerran power stations) and two different activators (NaOH and Na2O·1.5SiO2). The curing of the binders was performed at room temperature (20±5°C) for 24 hours followed by sealed curing at 75°C for 12 hours and then 7 days of ageing at ambient conditions. When the geopolymer binder specimens were put in contact with water at the bottom, efflorescence took place very quickly (within 3 hours) on NaOH-activated specimens. The effect of efflorescence on the compressive strength and modulus was studied by comparing specimens under dry, water contact and water immersion conditions for 28 days. The results showed that in general the dry samples achieved highest compressive strength while the water immersed samples exhibited the lowest strength. The NaOH-activated specimens under water contact conditions suffered intense efflorescence due to porous structure and exhibited lower strengths than those under leaching conditions. The compression modulus was tested to be proportional to the compressive strength. Both water contact and immersion seemed to be negative for the strength development. This issue should be considered when geopolymer products are applied under humid conditions.