Benchmarking PFA grouts for magnesium sulfate bearing exposures

Abstract

This paper describes a study carried out to examine the sulfate resistance of a wide range of pulverized-fuel ash (PFA) grouts. A number of material variables were considered reflecting those used in practice, including PFA content, and cement and PFA material characteristics (between sources). Several exposure environment conditions were also tested. It was found that under Class 5 sulfate exposure conditions, as classified in BRE Digest 363 (upper limit of Class XA3 to prEN 206), expansion was reduced with increasing PFA content. For grouts with PFA replacements in excess of 75% by weight, virtually no expansion was measurable over the test period. PC and PFA from different sources had only a minor effect on performance. However, the combination of PFA with sulfate resisting cement was found to reduce expansions by about 50% in comparison to corresponding PC/PFA grouts at PFA levels up to 75%. In very aggressive exposures (twice Class 5), it was found that only the very high PFA content grouts (>90% PFA) exhibited no visible damage after 12 months exposure. The influence of the additional presence of magnesium chloride appeared to modify the nature of damage occurring, but tended to inhibit it. The practical implications of the study are considered and means of specifying and categorising PFA grouts for sulfate resistance tentatively proposed.