Creep Behavior and Its Prediction for Normal Strength Concrete Made from Crushed Clay Bricks as Coarse Aggregate

摘要

To study the effect of crushed clay bricks as coarse aggregate on creep behavior of concrete, a comprehensive testing program was conducted. Concrete cylinder specimens having characterisiic or specified compressive strength of 17.2, 24.0, and 27.5 MPa were prepared from both natural stone and crushed clay brick aggregate. Mix design ratios were evaluated in a way so that volumetric content of coarse aggregate, both brick and stone, remained same for all concrete samples. Specimens were subjected to creep testing at the 7th and 28th day after casting and creep strain data were recorded up to 300 days. Results show that although strength and other environmental parameters remain the same, concrete made from crushed clay brick as coarse aggregate have a higher creep strain than that of concrete made from natural stone aggregate. This increase in creep strain ranges from 30% to as high as 45% for the 300-day loading history considered. Additionally, to select an appropriate model to predict creep in brick aggregate concrete, the effectiveness of five widely used prediction models were examined. Predicted creep strain from ACI 209R, CEB-FIP, B3, GL2000, and Eurocode 2 models were compared with experimental results. By using statistical analysis, the authors established that prediction of creep by GL2000 model is closest to the experimental results. Finally, a modification factor has been proposed that may be incorporated so that prediction of creep strain by the GL2000 model in brick aggregate concrete becomes more realistic.