Improving the strength properties of recycled asphalt aggregate concrete

The querying of aggregate, for use in the manufacture of concrete, can have adverse environmental and ecological effects. The replacement of gravel aggregate with recycled (reclaimed) asphalt would help in the reduction of these effects. It can also help in reducing the quantity of recycled asphalt obtained from road re-surfacing that would otherwise be disposed off in landfill sites. The applications of concrete containing recycled asphalt have been very limited due to its low strength. This study investigates the feasibility of improving the strength of recycled asphalt concretes. This would increase the potential for using this type of concrete as an alternative to normal concrete, especially where medium strengths might be required. Concrete strength improvements would be achieved by changing the surface characteristics of recycled asphalt aggregate. This has been sought by using two methods; mechanical roughening and chemical solvent etching. It has been possible to improve the strength of concrete containing recycled asphalt to values similar to that of normal (gravel) concrete, by applying the mechanical roughening technique. Chemical etching has no effect on strength improvement of the concrete. The concretes have also been tested using non-destructive methods in the form of ultrasonic pulse velocity and rebound number. The effects of replacing gravel with different percentages of recycled asphalt on the strength, pulse velocity, and surface hardness of concrete are considered initially. The inclusion of recycled asphalt at 25% has resulted in the reduction of strength. The strength decreases further with an increase in the percentage (up to 100%) of recycled asphalt. All investigations were performed on early age concrete (1-28 days).