1.2.2. Other alternative materials

Steel slag aggregate is a good example of synthetic aggregates obtained from by-products of industrial processes. It has good binding properties with bitumen due to its high calcium oxide content (NatSteel 1993). The angular shape of the aggregates helps to form strong interlocking structure. Road paving with steel slag aggregate show

• good skid resistance
• mechanical strength able to withstand heavy traffic and surface wearing.

Also, many industrial and other waste products like fly-ash, cement kiln dust, incenerated refuse etc. have been successfully used to produce synthetic aggregates.

Mixing bitumen with rubber (natural or crumb form) sometimes poses difficulty. As an alternative approach, tiny crumb rubber pieces can be mixed with aggregates - known as dry-process. Research shows improved fatigue performance for this kind of materials (Sibal et al. 2000), also, this process does not require any modification to the existing batch mixing plant.