There is a critical shortage of natural aggregate. Large quantities of waste concrete are produced from curb and gutter, sidewalk, bridges, buildings, etc. Using this waste concrete as a recycled concrete aggregate (RCA) conserves virgin aggregate, reduces the impact on landfills, decreases energy consumption and potentially provides significant cost savings. However, there are still many unanswered questions on the beneficial use of RCA in concrete pavements. This paper identifies several mix designs containing RCA that show encouraging results in both the laboratory and field testing. The Center for Pavement and Transportation Technology (CPATT) at the University of Waterloo in partnership with Dufferin Construction and the Cement Association of Canada successfully placed three RCA concrete test sections. The coarse RCA used in the mix designs was selected to minimize impurities and limit the amount of interfacial transition zones. Waste curb and gutter and sidewalks were used to provide consistency in the RCA properties. Fine RCA was not used since it may contain large amounts of impurities that result in concrete strength loss. Twelve mix designs were laboratory tested using coarse RCA amounts of 0% (control), 15%, 30% and 50%, and cement contents of 315 kg, 330 kg, and 345 kg. Since all test mixes exceeded 30 MPa at 28-days, the lowest cement content mixes were selected for field testing. Four test sections placed at the CPATT test track allow monitoring of in-service RCA pavements. Concrete containing 19 mm coarse RCA results in similar or improved performance compared to non-RCA concrete.
Abstract