Long-term strength development and durability index quality of ambient-cured fly ash geopolymer concretes

Abstract

While the geopolymer binder system is considered the foremost eco – friendly alternative to conventional Portland cement, its long – term performance has not yet been fully established. This study evaluated the long – term strength development and durability performance responses of fly ash (FA) – based geopolymer concrete mixtures activated using combined sodium silicate and sodium hydroxide solutions mixed at a varied ratio of the former to the latter, ranging from 0.72 to 4.89. The foregoing investigation was done focusing on effects of physico – chemical parameters comprising SiO2/FA, Na2O/FA and H2O/FA ratios. Concrete samples were cast then ambient – cured for one year, or oven – cured at 60 °C for 24 h followed by ambient – curing until testing. Various tests were done at 28 days or one year, including compressive strength, durability indexes, water absorption and volume of permeable pores. The durability indexes measured were water sorptivity, oxygen permeability and chloride conductivity. It was found that ambient – cured geopolymer concretes exhibited strong long – term strength gains of 60 to 90%, normal pore structure characteristics and good durability quality. However, the chloride conductivity test seemed to display erratic outputs, possibly due to ion fluxes, hence further research is needed to evaluate the method’s suitability for testing geopolymer concretes.