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Surfacing Aggregate


This type of aggregate is used in the production of the surface layers or seals for road construction.
They are applied by chip spreaders, and comply with particular specifications.
The process: Spay Bitumen binder onto a prepared base-course layer and then apply aggregate particles immediately after, then roll to achieve a mosaic pattern. The Binder will move into voids between particles.

Seals in Use:

  • Single Seals – 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 needed if stone exceeds 13.2mm. Pre-coating may improve adhesion.
  • Double Seals – Consists of two layers, the top containing smaller aggregate then the bottom. Large aggregate is used for heavy traffic roads.
  • Slurry Seals – constructed to achieve uniform texture on roads with varying surfaces and also as pre-treatment before applying single/ double seals (not advised for smooth textured surfaces)
  • Sand Seals – low-cost construction for low traffic roads. Used as pre-treatment or dust palliatives for Singe/ Double layer surfaces. Water may be required to assist with the screening process, and cleaning the sand of excess fines.

Additional requirements to apply:

  1. Hardness – ACV should not exceed 21% when using standard testing methods, and 10% FACT value must be at least 210kN. The Wet: Dry ratio should be at least 75%. PSV should be at least 50%, unless otherwise specified or approved by the engineer.
  2. Particle Shape – Where stated in the project, the average least dimension (ALD) should comply with the figure indicated.

Sand properties and sand equivalent – Approved crusher and should be used for sand or slurry, obtained from parent rock with an ACV not exceeding 30%, or a mixture of crusher sand not more than 25% clean natural sand. (must also comply with project specifications)

May 2024