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This study investigates chloride ingress into alkali-activated slag/fly ash (AA-S/F) concretes with various ratios of slag to fly ash (80/20, 60/40, 40/60 and 20/80). Alkaline activators were a mixture of sodium hydroxide and sodium silicate to obtain between 6-8% sodium hydroxide (NaOH) concentration by weight of cementitious material. The SiO2/Na2O ratios (silica modulus, Ms) of mixtures were 0.45, 1.0 and 1.25. Tests applied included typical fresh and hardened properties, air content, slump, compressive strength, bulk resistivity and non-steady state chloride migration. The results show that while attractive engineering properties can be achieved, the chloride ingress in the AA-S/F concretes studied here with ≥ 20% fly ash is moderate to high and this may make them unsuitable for use in reinforced concrete in chloride environments.

One of the key drivers for the adoption of Alkali Activated Material (AAM) over recent years is the reduction in CO2 emissions compared to Portland Cement and it is well known that AAM based concretes have superior strength characteristics in comparison to Portland Cement based concretes. However, many consider the durability of AAMs to be an unproven issue and therefore in the past decade many tests and investigations like this one have been undertaken to obtain a better understanding of the durability of AAM based concretes. The purpose of this paper is to assess the carbonation resistance of AAM concretes based on Ground Granulated Blast-furnace Slag (GGBS) and Pulverised Fly-Ash (PFA). The carbonation depth and strength change of four mix designs has been measured; two based on GGBS and two based on a blend of GGBS and PFA. A combination of both Sodium Hydroxide and Sodium Silicate was used as activator solution for various mix designs. This was completed as part of a wider study of AAM based concretes properties and overall durability. For investigating the effect of differing percentages of relative humidity on the carbonation of AAM concretes under accelerated condition, a constant CO2 level of 5% which is greatly elevated from the atmospheric level, as well as a constant temperature of 20°C was considered. Then the carbonation depths and strength changes of all mixes were tested at 50%, 65%, 75% and 85% humidity levels.

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.

One of the binder systems with low environmental footprint is alkali activated slag concretes (AASC), made by adding alkalis such as sodium hydroxide and sodium silicate to industrial by-products such as ground granulated blast furnace slag (GGBS). Whilst they have the similar behaviour as that of traditional cement systems in terms of strength and structural behaviour, AASC do exhibit superior performance in terms of abrasion and acid resistance and fire protection. In this article, the authors focus their attention on chloride ingress into different grades of AASC. The mix variables in AASC included water-to-binder, binder to aggregate ratio, percentage of alkali and the SiO2/Na2O ratio (silica modulus, Ms). The first challenge is to get mixes for different range of workability (with slump values from 40mm to 240mm) and reasonable early age and long term compressive strength according to each one. Then the chloride diffusion and migration in those mixes were measured and compared with same normal concretes in the existed literature based on chloride penetration depth. Comparing the chloride ingress between tradition concretes and AASCs is worthwhile to prove the possibility of increasing concrete lifetime in proximity to sea and deciding while such concretes are practical for use. Findings show that compared to the PC concretes, the AAS concretes have lower rate of chloride ingress.

Researchers are focusing their attention on alternative binder systems using 100% supplementary cementitious materials as it allows better control over the microstructure formation and low to moderate environmental footprint. One such system being considered is alkali activated slag concretes (AASC), made by adding alkalis such as sodium hydroxide and sodium silicate to ground granulated blast furnace slag (GGBS). Whilst they have a similar behaviour as that of traditional cement systems in terms of strength and structural behaviour, AASC are reported to exhibit superior performance in terms of abrasion,acid resistance and fire protection. In this article, the authors investigate chloride ingress into different grades of AASC. The mix variables in AASC included water to binder, and binder to aggregate ratio, percentage of alkali and the SiO2/Na2O ratio (silica modulus, Ms). The first challenge was to develop mixes for different range of workability (with slump values from 40mm to 240mm) and reasonable early age and long term compressive strength. Further chloride ingress into those mixes were assessed and compared with the data from normal concretes based on literature. Findings show that compared to the PC concretes, the AAS concretes have lower rate of chloride ingress.