Speciality Aggregate

Used in the production of the surface layer of road construction, surfacing aggregates are usually applied by chip spreaders.

Surfacing Aggregates

Surfacing Aggregates are the aggregates used in the production of the surface layers or seals for road construction. These are usually applied by chip spreaders and comply with certain specifications.

Types of seals in use:

  • Single Seals are used in the construction of new surfaces as well as rehabilitation of existing surfaces. Traffic volume determines the aggregate size and a second binder layer may be applied if stone exceeds 13,2mm. Pre-coating may improve adhesion.
  • Double Seals are constructed in two layers, with the top layer containing smaller aggregate than the bottom. Larger aggregate sizes are used for roads carrying heavy traffic.
  • Slurry Seals are used to achieve uniform texture on roads with varying surfaces and also for pre-treatment before applying single or double seals (not advisable for smooth textured surfaces).
  • Sand Seals are used in low-cost construction, for low traffic roads, as dust palliatives and also as pre-treatment for single- or double-layer surfaces. Water may be required to assist in the screening process and to clean the sand of excess fines.


Ballast is aggregate material used as the foundation in the construction of rail tracks and is usually made from crushed stone. It is packed between, below and around the rail sleepers or ties, and serves a number of purposes.

These include:

  • Facilitating drainage of water around the tracks.
  • Bearing and transmitting the load from the railroad ties.
  • Providing uniform support.
  • Anchoring the track.
  • Preventing vegetation growth.
  • Resisting aggregate degradation.
  • Facilitating maintenance operations.
  • Resisting fouling.
  • Minimising climatic influences.


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