Concrete Performance Using Low-Degradation Aggregates

The durability of Portland cement concrete (PCC) has long been identified as a concern by transportation communities around the United States. In this study, the long-term performance of two batches of concrete incorporating either low-degradation (LD) or normal (NM) aggregates subjected to freezing and thawing conditions was experimentally studied. The freezing and thawing test method (ASTM C666) was followed to condition all the test samples. Dynamic modulus and fracture energy for both groups of concrete samples after different numbers of freeze-thaw cycles were measured through nondestructive modal and cohesive fracture tests, respectively. Due to the higher air content in LD concrete, surface scaling was less severe under frost action. Test results showed that different aggregate degradation has an important effect on the freeze-thaw resistance of the concrete and the rate of decrease in fracture energy with number of freeze-thaw cycles for the LD concrete is higher than for the NM concrete. Compared to the dynamic modulus of elasticity, the fracture energy is a more sensitive parameter for evaluating concrete degradation caused by the frost action. Thus, the degradation of aggregate in concrete can be better evaluated by the cohesive fracture test. Additional research is needed to identify an appropriate threshold for when aggregate degradation properties become a concern. Until that time, it is recommended that WSDOT maintain their current restrictions on using low-degradation aggregates in concrete.