Understanding Different Australian Asphalt Mix Types: AC7, AC10, AC14, AC20, SMA & OGA

Introduction

When you read a civil engineering drawing, a council vehicular crossover specification, or an itemised quote from a Sydney paving contractor, you will encounter alphanumeric codes like AC7, AC10, AC14, AC20, SMA, and OGA.

What do those numbers and letters actually mean? Choosing the wrong asphalt mix—such as laying a coarse, bony AC20 base mix on a residential driveway where a smooth AC10 wearing course belongs, or laying a fine AC7 footpath mix in a heavy truck dock—leads to poor surface appearance or rapid structural rutting. Here is the definitive plain-English guide to Australian asphalt mix designations used in AC10, AC14 and AC20 asphalt paving across NSW (Austroads Pavement Work Tips, Boral Asphalt).

1. Dense Graded Asphalt (DGA): The Workhorse AC Series

Dense Graded Asphalt (DGA) is the standard structural and wearing-course hot mix used across 85%+ of Australian roads, car parks, and driveways. In NSW specifications, DGA mixes are prefixed with AC (Asphaltic Concrete) followed by a number (5, 7, 10, 14, 20, or 28) that indicates the nominal maximum aggregate stone size in millimetres:

AC7 (or AC5) – Fine Dense Graded Asphalt

• Maximum Stone Size: 7 mm (or 5 mm).
• Recommended Compacted Thickness: 20 mm – 35 mm.
• Surface Texture: Very fine, tight, smooth, and uniform matte finish.
• Best Used For: Pedestrian footpaths, shared bicycle paths, school playgrounds, tennis/basketball courts, fine residential driveways, and thin “corrective regulation” levelling courses used to fill shallow depressions before laying a main overlay.

AC10 – Medium Dense Graded Asphalt (Most Popular All-Round Wearing Course)

• Maximum Stone Size: 10 mm.
• Recommended Compacted Thickness: 30 mm – 45 mm.
• Surface Texture: Smooth, dense, and visually appealing blacktop with excellent waterproofing and low tyre noise.
• Best Used For: Residential driveways, strata complex roadways, standard commercial car park bays and circulation aisles, and council local residential streets.

AC14 – Heavy-Duty Dense Graded Wearing Course

• Maximum Stone Size: 14 mm.
• Recommended Compacted Thickness: 40 mm – 60 mm.
• Surface Texture: Slightly coarser, interlocking stone texture offering higher shear strength and wet-weather skid resistance.
• Best Used For: Commercial shopping centre delivery lanes, industrial estate roads, council collector and arterial roads, bus lanes, and heavy-duty industrial asphalt mixes.

AC20 – Structural Base / Intermediate Course Asphalt

• Maximum Stone Size: 20 mm.
• Recommended Compacted Thickness: 60 mm – 100 mm+ per compacted lift.
• Surface Texture: Coarse, large-stone structural skeleton (more open texture if left uncovered).
• Best Used For: Deep-lift structural asphalt base layers beneath an AC10 or AC14 wearing course in industrial hardstands, container yards, heavy road reconstructions, and full-depth utility trench restorations.

2. Specialty High-Performance Asphalt Mixes (SMA, OGA, Warm Mix & Cold Mix)

Specialty Mix Type	How It Differs from Standard DGA (AC)	Primary Applications in Sydney & NSW
Stone Mastic Asphalt (SMA10 / SMA14)	A gap-graded mix with a high proportion of coarse crushed stone (forming direct stone-on-stone contact) bound with a rich mastic of polymer-modified bitumen, filler, and cellulose fibres.	Extreme Rut & Scuff Resistance: Heavy industrial forklift yards, truck turning circles, bus stops, and high-volume intersections.
Open Graded Asphalt (OGA10 / OGA14)	Engineered with very little fine sand so compacted air voids sit at 18%–22%, creating interconnected drainage channels inside the mat.	Water-Draining / Low-Noise Wearing Course: High-speed motorways (reduces wet-weather tyre spray and noise) and free-draining sports courts.
Warm Mix / Recycled Asphalt (RAP)	Manufactured with foaming additives/waxes at lower plant temperatures (~120°C–135°C) and incorporates Reclaimed Asphalt Pavement (RAP) (Boral Asphalt, Fulton Hogan).	Sustainable council, government, and commercial projects targeting lower embodied carbon and longer haul/compaction windows in cool weather.
Cold Mix Asphalt	Pre-mixed aggregate and cutback/emulsion bitumen treated with slow-curing oils so it remains workable in bags or stockpiles at ambient temperature.	Temporary Emergency Patching Only: Filling sudden winter potholes or overnight utility cuts until permanent hot mix (AC10/AC14) can be laid.

The Golden Engineering Rule: Minimum Layer Thickness vs Stone Size

Why can’t you lay a coarse AC14 or AC20 mix at just 25mm thick? According to Austroads Guide to Pavement Technology Part 8, the compacted thickness of any asphalt layer must be at least 2.5 to 3.5 times the nominal maximum stone size so the stones can rotate and nest together under the roller without being crushed or dragging under the paver screed:

Asphalt Mix	Nominal Stone Size	Absolute Minimum Compacted Thickness	Optimal Compacted Thickness Range
AC7	7 mm	20 mm	25 mm – 35 mm
AC10	10 mm	25 mm – 30 mm	30 mm – 45 mm
AC14	14 mm	35 mm – 40 mm	40 mm – 60 mm
AC20	20 mm	50 mm – 60 mm	65 mm – 100 mm

Understanding Bitumen Binder Grades (C170, C320 & PMB)

Alongside the aggregate size (AC10 / AC14), engineers also specify the stiffness of the bitumen glue inside the mix:

• Class 170 (C170): Standard softer viscosity bitumen used in spray sealing and low-stress residential paths/driveways where long-term flexibility is prioritised.
• Class 320 (C320): Stiffer standard paving-grade bitumen used across most Sydney commercial car parks and council roads to resist summer rutting.
• Polymer Modified Binders (PMB – e.g., A15E, A20E): Bitumen reinforced with synthetic elastomers (rubbers) for heavy industrial hardstands, roundabouts, and high-stress truck zones.

Frequently Asked Questions

Which mix is best for a standard commercial car park in Sydney?

For passenger car parking bays and light circulation aisles, 40mm of AC10 (C320) provides the best balance of smooth visual presentation and durability. For the main entry driveway and waste-truck loading zone, upgrading to 45mm–50mm of AC14 (C320 or PMB) (over a deep-lift AC20 base if heavy semi-trailers enter) prevents wheel rutting and power-steering scuff marks.

Conclusion & Next Steps

Knowing the difference between AC7, AC10, AC14, AC20, and SMA empowers you to specify the exact performance your property requires. To see how these mixes are applied in car parks, read our Commercial Car Park Surfacing Guide.

Need expert advice on the right mix specification for your Sydney project? Call National Road Surfacing on 0475 013 264 or request a quote online.