Freeze-Thaw Durability of Concrete with Natural and Recycled Concrete Aggregates Using Air-Entraining Admixture

Freezing and thawing cycles are one of the most damaging factors that affect the durability of concrete. The damages caused by cyclic freeze-thaw (F-T) action can be divided into two factors. The first factor is an increase in internal cracking, which causes the loss in relative dynamic modulus (RDM) of the concrete, and the second factor is surface scaling, which leads to weight loss of the concrete. In this study, the durability of concrete made by replacing natural coarse aggregates (NCA) with various percentages of recycled concrete aggregates (RCA) is measured for an F-T test. Also, some tests have been conducted with the addition of air-entraining admixture (AEA). Prior to mixing the concrete, both NCA and RCA were characterized to determine their suitability as a construction material. Concrete mixes consisting of 0, 20, 40, 60, 80, and 100 % replacement (by weight) of NCA with RCA were prepared. The same concrete mixes were prepared again with the addition of AEA. All specimens were tested for compressive strength after a curing period of 7, 14, and 28 days. The compressive strength of the concrete made with different percentages of RCA decreases as the percentage of RCA increases. After 28 days of curing, sample with 0, 40, and 100 % replacement of NCA with RCA were placed without AEA in the F-T chamber, along with 0, 20, 40, 60, 80, and 100 % NCA replacements containing AEA. After several cycles of freezing and thawing, the RDM, change in weight, and change in length were measured. The RDM loss and weight loss were noticed, as the cyclic F-T durability increased. It has also been observed that concrete mixes containing AEA were still durable after 300 cycles of freezing and thawing; however, the specimens without AEA failed before 150 cycles.