MOT Type 3 Subbase: What is it?

What is MOT Type 3 Subbase?

MOT Type 3 Subbase or just Type 3 is an open graded unbound mixture of aggregates. The material grading requirements are defined in Clause 805 of the Standards for Highway Works.

Type 3 will be crushed down to a size of 80mm down to dust. It differs from MOT Type 1 because the larger sieve sizes are sued when processing the aggregates meaning the final material is much coarser.

It’s used as a subbase in construction work and can be used as an alternative to Type 1 when better drainage qualities are required.

What materials can be used to produce Type 3?

It can be produced using both Quarried & Recycled materials.

This includes crushed rock, crushed blast furnace slag, manufactured aggregates or recycled concrete aggregate.

What are the specifications for Type 3 Subbase?

If used in the construction of highways then Type 3 must meet the requirements set out in Clause 805 of the Specification for Highway Works.

You can see the specifications below:

Summary grading requirements for Type 3 (open graded) Unbound Mixtures

Mixture and grading requirement categories for unbound mixtures

Requirements for aggregates used in unbound mixtures