Effect of curing on resistance to deicing salt scaling, freezing-thawing and chloride penetration of fly ash concrete

Abstract

The four concrete mixtures used in this study contained 0%, 15%, 30%, and 40% fly ash replacing portland cement by mass. To determine the effect of curing type, three different curing conditions were used. Curing Type 1 was the uncontrolled curing condition; the specimens were kept inside the laboratory after demolding till the time of testing. Curing Type 2 was the standard curing condition; specimens after demolding were put in 20 0C water for 1 week then kept in 20 0C curing room. Curing Type 3 named as hot curing; specimens after demolding were put in 30 0C water for 1 week and then kept in 20 0C curing room till they are tested at 28 and 56 days of age. The results revealed that fly ash replacement generally had negative effects on mechanical properties. The negative effects are more distinguishable when the specimens are not cured (Type 1) and less pronounced with moist curing (Type 2) and least with hot curing (Type 3). On the contrary, fly ash replacement generally had positive effects on capillary absorption, chloride permeability (determined by AASHTO T 277), deicing salt scaling (tested according to ASTM C672) and freezing-thawing resistance with the exception that these properties also were negatively affected in the uncontrolled cured specimens. Highest durability performance was observed in the hot cured (Type 3 ) specimens followed by moist curing (Type 2) ones, and the lowest results were those of the non-cured specimens (Type 1).