What it is called, by market
One concept, four markets. Where a name means something else locally, the card says so rather than leaving you to find out on site.
United Kingdom
Close, not identicalsub-base
also hardcore, MOT Type 1, Type 1
"MOT Type 1" is a specific graded crushed rock to a published grading envelope; "hardcore" is the older and looser word, historically including broken brick and demolition arisings.
United Statesyours
Close, not identicalaggregate base
also crusher run, base course, road base
Designations are set by state departments of transportation rather than nationally, so "crusher run" describes the production method and the actual grading depends on the specifying agency.
Canada
Close, not identicalgranular base
also Granular A, Granular B, crusher run
Provincial designations such as Granular A and Granular B name specific gradings, so the letter matters and does not translate to a British or American product name.
Australia
Close, not identicalroad base
also DGB, dense graded base, crushed rock
Australian designations are set by state road authorities to their own specifications, so a class name identifies a grading in that state rather than a material available everywhere.
The governing standard, by market
United Kingdom
SHW Series 800
Unbound mixtures for sub-base — grading and compaction requirements.
United States
AASHTO M147
Materials for aggregate and soil-aggregate subbase, base and surface courses.
Calculators for this
Each works in either measurement system, and the terminology on the page follows whichever market you have selected.
Frequently asked questions
- Is hardcore the same as sub-base?
- Not quite, and the difference is a specification. Sub-base names the LAYER and, in modern British practice, a material graded to a published envelope — MOT Type 1 being the familiar one, a crushed rock with a controlled range of particle sizes so that it compacts to a dense, interlocked, load-spreading layer. Hardcore is the older and looser term, historically covering broken brick, demolition arisings and whatever hard material was available, laid to fill and to raise levels. The two are often used interchangeably on domestic work, and the distinction matters where performance is required: unspecified hardcore may contain material that degrades, holds water, or contains sulfates that attack concrete above it.
- Why do the designations not translate between markets?
- Because they are product specifications issued by different authorities, not descriptions of a generic material. A British MOT Type 1 is defined by a grading envelope in a national specification for highway works. American aggregate base designations are issued by individual state departments of transportation, so the same trade name can mean different gradings in neighbouring states. Canadian Granular A and B are provincial designations, and Australian road base classes are set by state road authorities. So the correct approach when reading a foreign specification is to find the grading and the compaction requirement it actually calls for, and match those against a locally available product, rather than to look for the nearest-sounding name.
- How thick should it be?
- It depends on the subgrade beneath and the loading above, which is why it is designed rather than defaulted. The layer's job is to spread concentrated loads from the surface into ground that cannot take them directly, so a weak or wet subgrade needs a thicker layer than a firm one, and a drive taking occasional cars needs far less than a yard taking loaded lorries. The subgrade's strength is measured — by CBR or an equivalent — and the thickness follows from that and the design traffic. Thickness is also constrained from below by compaction: the layer is built in lifts a compactor can actually densify through, so a thick sub-base is several passes of placing and compacting rather than one.