Impact of fly ash production and sourcing changes on chemical and physical aspects of concrete durability

Abstract

Changes in coal-fired power technology have recently been introduced, influencing emissions and efficiency, which may affect fly ash. Similarly, shortages of low lime fly ash, with power stations being taken out of service, mean recovery/processing of material from wet holding areas (e.g. stockpiles) is receiving attention. Previous research has considered the effect of these fly ashes on chloride ingress and carbonation of concrete. In the current study, chemical (sulfate attack and alkali-aggregate reaction (AAR)) and physical (freeze–thaw (salt) scaling and abrasion) processes causing concrete deterioration are investigated. These used laboratory tests and practical concrete mixes, with comparisons made against three reference fly ashes of different fineness, and data from earlier studies (late 1990 s/early 2000 s). The results indicate minor differences between fly ash concretes for sulfate attack and AAR, where small expansions were obtained. Although specific fly ash influences were not identifiable, air-entrained concretes gave acceptable freeze–thaw scaling performance (0.45 water/cement ratio), while abrasion generally followed concrete strength. Similar effects were found to the earlier studies. The changing technologies and wet storage may influence fly ash characteristics, however, they generally follow typical behaviour for the concrete properties examined and suggest continued suitability for use.