Effect of High-Temperature Curing on the Compressive Strength of Concrete Incorporating Large Volumes of Fly Ash

摘要

This paper provides results about the effect of using different types of curing on the compressive strength of concrete both with and without large volumes fly ash (FA). In all the concrete mixtures, the portland cement content was 200 kg/m~3. The FA amount was varied from zero to 33, 43, 50 and 56 percent by mass of the total binder, and a superplasticizer was used to obtain 200-220 mm slump. The compressive strength was tested at the age of 3,7, 14, 28, 56 days and 6 months. The compressive strength of the portland-cement concrete made at 35°C was reduced by about 11 % at 28 days when compared to that of concrete made at 23°C with ASTM standard curing. With continuous moist-curing of fresh concrete, there was no strength loss of concrete made at 35°C. FA concrete specimens that were under intermittent spray-water curing at 35°C in the laboratory (every four hours) for 7 days and then under ambient conditions gave increased compressive strength up to the time of testing i.e. 6 months. Reduced strength was obtained for 3 days intermittent curing. Higher strength was obtained as the amount of FA was increased for a given amount of the Portland cement. The FA concrete mixtures cast at 35°C were cured by covering the specimens with membrane curing compound and placed under ambient conditions until age of testing, the strengths were lower than reference concrete by about 20% to 30% at 28 days, and 30% to 50% at 56 days. It is necessary that enough curing water to promote the pozzolanic reaction is used. The membrane curing did not allow the ingress of water to the concrete mass.