BENCHMARKING PFA GROUTS FOR MAGNESIUM-SULFATE BEARING EXPOSURES

This paper describes a study carried out to examine the sulfate resist ance 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 (be tween sources). Several exposure environment conditions were also test ed. It was found that under Class 5 sulfate exposure conditions, as cl assified in BRE Digest 363 (upper limit of Class XA3 to prEN 206), exp ansion was reduced with increasing PFA content. For grouts with PFA re placements in excess of 75% by weight, virtually no expansion was meas urable over the test period. PC and PFA from different sources had onl y a minor effect on performance. However, the combination of PFA with sulfate resisting cement was found to reduce expansions by about 50% i n comparison to corresponding PC/PFA grouts at PFA levels up to 75%. I n very aggressive exposures (twice Class 5), it was found that only th e 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 su lfate resistance tentatively proposed.