Blacktop, or asphalt, pavement is made of a mixture of sand, gravel, and stones mixed with the asphalt itself. The asphalt is a petroleum oil which is just about the last stuff to come out of the refinery. It melts at a fairly high temperature. The pavement plant mixes the gravel with the hot asphalt in such a way as to coat all the material fairly evenly. It is placed, hot, on the roadway, smoothed, and rolled. It then cools and solidifies. When fresh it is very black, because all the gravel is coated with the asphalt oil. It can also be very slippery when it gets wet, because after all it is a coat of oil. It appears to fade as it ages, but that is really the asphalt coating wearing away and exposing the gravel itself. There is usually only about 5% to 10% asphalt in the mixture, and its purpose is to act as a binder or glue to hold the gravel in place. The asphalt never "sets" like concrete, but will melt again if heated. That's why your sidestand will sink into the blacktop on a really hot summer day, and why ruts form in the blacktop on roads with a lot of truck traffic.