Resistance of alkali activated concretes to sulphate attack

The article highlights the resistance of two types of alkali activated material (AAM) concretes to sulphate attack. AAM considered were made of 100% ground granulated blast furnace slag (GGBS) and a blend of GGBS and pulverised fuel ash (PFA). Sodium hydroxide and sodium silicate based activator was used for this study. The material presented here is part of a wider study into Alkali Activated Materials to characterise them for their durability performance. Although it is accepted that AAM based concretes had superior strength characteristics to Portland cement based concretes, there is still debate over the durability of AAM. The mass loss, strength and expansion of four mixes were studied for a period of 56 days. Concrete cubes were exposed to water, magnesium sulphate, sodium sulphate and calcium sulphate solutions and a sulphuric acid solution. Mass and ultrasonic pulse velocity across each sample were measured once a week. For studying expansion concrete prisms were immersed in water and the salt solutions and changes to the length of each sample was measured every week. Dry prisms kept in ideal condition were used as a reference. For the first 56 days of immersion the Blended samples appeared to perform better than the GGBS samples.