Long term durability properties of class F fly ash geopolymer concrete

The environmental impact from the production of cement has prompted research into the development of concretes using 100 % replacement materials activated by alkali solutions. This paper reports the assessment of a number of key durability parameters for geopolymer concrete made from fly ash activated with sodium silicate and sodium hydroxide. Properties investigated have included workability, compressive strength, water sorptivity, carbonation, chloride diffusion and rapid chloride permeability. Microstructure studies have been conducted using scanning electron microscopy and energy dispersive X-ray spectroscopy. The results showed that both the geopolymer concretes with activator modulus 1.00 and 1.25 gave durability parameters comparable to Ordinary Portland and blended cement concretes of similar strength, while the geopolymer concrete with an activator modulus of 0.75 displayed lower durability performance. However, there is a concern over the long term performance of the geopolymer concretes with activator modulus of 1.00 and 1.25 when considering chloride induced corrosion of reinforcing steel due to the initial pH and long term chloride diffusion coefficient.