Grouted or Penetration Macadam:

This is a specification where the binder is sprayed on a compacted layer of stone aggregates and is allowed to penetrate and bind the aggregates. A layer of intermediate aggregates, called key aggregates, is spread on the layer and rolled. A seal coat is provided to seal the surface.

For a 50 mm compacted thickness, the quantity of coarse aggregates is 0.60 cu m per 10 sq m area, the quantity of binder is 50 kg per 10 sq m, and the quantity of key aggregates is 0.15 cu m per 10 sq m. The seal coat is similar to the seal coat provided for a PC.

The advantage of penetration macadam is that it does not require a mixing plant. The advantage is that it uses a high quantity of binder. The specification is hardly used now-a-days.