Effect of Curing on Strength and Chloride Penetration into Concretes Made with Portland and Blast Furnace Slag Cements

In this paper, portland cement concretes and concretes with blast furnace slag cement were studied to determine the parameters for strength and chloride permeability under different curing procedures. For this purpose, four concrete mixtures were made at two different water cement ratios of 0.45 and 0.65 with cement contents of 400 kg/m3 and 300 kg/m3, respectively. Reference mixtures and mixtures with blast furnace slag cement have been produced at both water cement ratios. After casting, the test specimens were subjected to three different curing conditions. In the first curing condition, the concrete specimens were left in a room for curing at uncontrolled temperature and humidity conditions. The second curing condition consisted of seven days of moist curing followed by curing at a controlled temperature and relative humidity. Finally, in the third curing condition, the concrete specimens were kept continuously in water bath till the time of testing. The compressive strength and splitting tensile strength of each concrete type were determined. In addition to these mechanical tests, the tests for determining concrete’s resistance to chloride ion penetration and water absorption capacity were conducted. All tests were carried out in accordance with the corresponding ASTM and AASHTO standards at the ages of 28 and 90 days. The results showed that the reduction in the moist curing period resulted in lower strengths and more permeable concretes. The permeability of the concretes containing blast furnace slag cement seemed to be more sensitive to poor curing than the portland cement concretes. The blast furnace slag cement concretes indicated better resistance to chloride ion penetration than the portland cement concretes for both water cement ratios. The water absorption capacity of the concretes made with blast furnace slag cement was somewhat higher than that of the portland cement concretes at the age of 28 days but a higher reduction was observed with increasing the age of concrete.