Durability of geopolymer materials in aggressive aqueous environments : acid attack, steel reinforcement corrosion and freeze-thaw attack

Geopolymer or alkali-activated concrete is a novel alternative to conventional Portland cement (PC) concrete. This thesis aims to advance the knowledge available by investigating the resistance of geopolymers against acid attack, steel reinforcement corrosion and freeze-thaw attack. The resistance of geopolymers to acid attack was investigated by exposing samples to mineral and organic acids as well as silage effluent. Mortar samples were used to assess the effect of acid exposure on physical properties and equivalent paste samples were used to assess the effect of acid exposure on leaching behaviour and microstructural properties. The effect of slag content and alkaline activator dosage on the acid resistance of fly ash geopolymers was also studied. It was discovered that neat fly ash geopolymers have significantly greater resistance to acidic media than blends of fly ash and slag. Furthermore, all geopolymer mixes investigated displayed superior performance when compared with PC. This was due to higher calcium content and several phases present in hydrated PC which are vulnerable to acid attack. The mechanisms of acid attack were also considered. The steel reinforcement corrosion was assessed by obtaining the chloride migration coefficient and carrying out a ponding test on concrete slabs which had embedded steel reinforcement bars. It was discovered that increasing the slag content and alkaline activ?tor dosage significantly improves the steel reinforcement corrosion resistance of fly ash geopolymers. The PC concrete performed much better than mixes with high fly ash content but mixes with high slag content provided comparable performance with PC concrete. Freeze-thaw resistance was investigated by performing a scaling test in the presence of both water and NaCl solutions. This revealed poor resistance of fly ash geopolymer concrete which improved as the slag content increased to be almost similar to that of PC concrete.