What Is DGB20?
DGB20 is a Densely Graded Base with a 20mm nominal size. It is designed for the upper structural layers of a pavement and is used as both base and sub-base.
- Nominal size: 20mm
- Specification: TfNSW Specification 3051 (Granular Base and Subbase Materials for Surfaced Road Pavements)
- Material: Class R1 recycled concrete
- Plasticity Index (Pi): 0%
The 20mm grading compacts to a dense, stable layer. That makes DGB20 the working layer that carries traffic loads close to the surface.
What Is DGS40?
DGS40 is the 40mm size in EBH’s Select / SMZ range. SMZ stands for Select Material Zone, the upper part of the formation that sits beneath the pavement layers. It is a densely graded select material used for subgrade replacement and formation layers.
- Nominal size: 40mm (the RMS Spec size; the same range also includes a 20mm Council Spec size)
- Specification: TfNSW Specification 3071 (Select Material for Formation Layers)
- Material: Recycled brick and concrete
- Plasticity Index (Pi): 0%
Because it is coarser than DGB20, DGS40 suits deeper pavement and formation applications, where the job is to build a strong, stable platform for the layers above. It isn’t intended to be the finished base layer.
A note on naming: RMS is now part of TfNSW, but “RMS Spec” is still widely used in the industry. Also, some council specifications use “DGS40” to mean a 40mm densely graded subbase under Spec 3051. If your project documents use that meaning, confirm with your engineer and let us know, so we supply the right product.
DGB20 vs DGS40: Side-by-Side Comparison
| DGB20 | DGS40 | |
|---|---|---|
| Product type | Densely Graded Base | Select / SMZ (Select Material Zone), 40mm size |
| Particle size | 20mm nominal | 40mm nominal |
| Application layer | Base and sub-base | Subgrade replacement and formation layers |
| Specification | TfNSW Specification 3051 | TfNSW Specification 3071 (RMS Spec size) |
| Material composition | Class R1 recycled concrete, Pi 0% | Recycled brick and concrete, Pi 0% |
| Typical use case | Road pavements and car parks | Deeper pavement sections and formation layers |
The simplest way to think about it: DGB20 is a working layer near the top of the pavement, while DGS40 is a supporting layer further down.
When to Use DGB20
DGB20 is the right choice when you’re building the structural layers closer to the surface. Typical applications include:
- Pavement base and sub-base construction
- Road surfaces and car parks
- Projects where the TfNSW 3051 granular base specification applies
If your design calls for a dense, compactable granular base that meets TfNSW 3051, DGB20 is the material to look at.
When to Use DGS40
DGS40 is the right choice when the design calls for a select material lower in the structure. Typical applications include:
- Subgrade replacement
- Formation layers
- Deeper pavement sections that call for a coarser select material
- Projects where the RMS Spec / TfNSW 3071 select material zone specification applies
If you’re replacing poor subgrade or building a formation platform, the SMZ range is designed for that role. A 20mm Council Spec size is also available in the same range, so check which size your design nominates.
How to Confirm the Right Specification
If you’re still unsure which product you need, a few quick checks will settle it:
- Check the project’s pavement design specification. The design will nominate the material type, grading and governing specification for each layer.
- Confirm with the project engineer. If the documents are unclear, or you’re working to a Council rather than a TfNSW requirement, a quick check saves costly rework later.
- Provide the specification when you enquire. Send EBH Environmental the relevant section of the design with your enquiry so we can supply the correct product the first time.
You can browse the full range, including the Select / SMZ products, on our products page.
