Asphalt is made of approximately 5% oil/binder and 95% crushed aggregate, of which 10-20% is often recycled (RAP – reclaimed asphalt pavement). Materials engineers design mixes with varying combinations of aggregate sizes/gradations and oil content to achieve various performance criteria. The goal is to create strength through the interlocking aggregates with just enough (but not too much) binder to effectively bond the aggregates. The most common asphalt mix is a “1/2” medium.” In this mix, the largest aggregates are ½” diameter with other smaller aggregates (3/8”, ¼” etc) down to sand size particles.