Durability of geopolymer concrete in marine environment

Abstract

Geopolymer binders which are produced by the reaction of solid aluminosilicate source materials such as fly ash, slag, and metakaolin with alkaline solutions represent a new class of inorganic polymer material with great potential to become a more sustainable alternative to Portland cement based binders. Due to the inorganic nature of geopolymers, they are intrinsically fire resistant and have been shown to have high acid resistance far in excess of traditional cements. However, the long-term durability and factors affecting structural deterioration caused by exposure conditions such as marine environments have had limited examination. Structures are susceptible to a number of mechanisms of degradation such as chloride and carbonation induced steel reinforcement corrosion. It is generally accepted that concrete durability is (to a large extent) governed by the concrete resistance to the penetration of aggressive substances. In marine or coastal zones, the most harmful substances contain chloride ions. This research work is aimed to experimentally investigate the microstructure, transport properties, chloride diffusion and carbonation of various types of geopolymer concrete including fly ash based, slag based and combined fly ash/slag geopolymer concretes. A systematic study on the effect of thermal curing and calcium content (sourced from slag) on the chloride diffusion resistance of geopolymers was conducted and results were interpreted by the means of nano and microstructural characteristics. The chloride binding capacity of low and high calcium content GPCs were investigated. The suitability of accelerated diffusion tests such as ASTM C1202 rapid chloride penetration test and NT BUILD 492 chloride migration test, initially developed for Portland cement concrete, has been investigated for geopolymer concretes and modification in test methods suggested and examined. Correlations between the modified ASTM C1202 data, the chloride migration coefficient and the chloride diffusion coefficient of geopolymers were established. Finally, performance-based recommendations for geopolymer concretes with various binders in marine environment were proposed.