Today, highway authorities face the increasingly difficult task of managing an ageing infrastructure. This task is further complicated by the decline in revenues and the substantial increase in traffic flow, speeds and axle weights. The use of pulverised fuel ash (Pfa) as a partial cement replacement in c('ncrete improves the properties of fresh concrete. Pfa's eff, in the absorption, abrasion resistance and some durability aspects of concrete would be favourable. Pfa, being a by-product of burning coal at electricity generating power stations, is cheaper than cement. The cost of new roads and the maintenance of existing ones would, therefore, be reduced if Pfa is used in the mixes. There has been concern, however, about the interaction of Pfa with air-entra inment. The effect of Pfa inclusion on the air-entraining agent (AEA) requirement, quality of void system and freeze-thaw durability of concrete was investigated. The most commonly used Pfa and AEA in the UK were tested. It was found that Pfa concrete requires 2 to 4 times as much AEA as the OPC counterpart for air contents below 5%. For higher air levels and concrete strengths of approximately 30 to 40 N/mm2, the AEA requirement for Pfa concretes can be more than 8 fold that for OPC ones. Provided that both types of concrete have similar air contents and strength, the air void system and freeze-thaw durability of Pfa and OPC concrete is almost identical. |
