Aggregate or metal strengthens the road by spreading wheel weight. It also protects and seals the earthworks and gives traction to vehicles so they can climb and brake. Metalling can be very expensive.
- The unmetalled section of the road has good shape and strength. Truck wheels have not deformed it
- Consistent thickness of metal was applied because of well-constructed subgrade
- Heavy rainfall has rilled the subgrade
- Earthworks should not be too far ahead of metalling, especially in ‘high risk’ areas
- Metal is being spread to the right depth
- The subgrade is not deformed or wheel rutted
- An excavator is an effective way to spread dumped metal
- Metal needs to be put down thicker than its final depth because it compacts down. See the thickness in front of, and behind the excavator
- Quality angular metal was applied
- There is a good mix of the aggregate size that provides strength and binds together well
- The metal can be graded, which is important for road maintenance
- Metalling is an expensive way to solve poor formation
- Huge volumes of metal were used to build up this corner. The arrow shows the size of a pinecone
- Metal was applied soon after completion of formation work
- Metal was applied to specification
- Metalling was done when the earthworks and weather were ok
- Metal was kept to the roadway and is not in the water tables
- A light roll at the right moisture helped tighten and seal the surface
- Some aggregate was wasted
- Metal is an expensive resource. It needs to be applied to the roadway, not the water tables or fill
- A grader was used to make the final shape before drum rolling
- The metal was at a good moisture content
- When using a grader, ensure that there are enough fines so that the metal can bind
- Grading can easily move larger stone to the outside of the road. This changes the aggregate size in the road pavement
- Do not use weed-infested metal stockpiles unless the area to be metalled already has those weeds
- Weeds are expensive and difficult to control once established
- Kill weeds in stockpiles before they get large enough to seed, not after they have seeded as in this photo