Open-Graded vs Dense-Graded Paver Base
Compare aggregate grading, water movement, layer compatibility and construction requirements without assuming one base system suits every paver project.
Dense-graded base uses a broad range of particle sizes, with smaller particles filling spaces between larger ones. Open-graded base has fewer fines and more connected voids. Either can belong in a paver assembly, but its bedding, subgrade, drainage and construction details must be coordinated.
Compare complete assemblies
| Issue | Dense-graded assembly | Open-graded assembly |
|---|---|---|
| Particle distribution | Multiple sizes and controlled fines | More open void structure with limited fines |
| Water movement | Managed through grading and project drainage details | Water can move through connected voids; destination still matters |
| Bedding compatibility | Conventional sand-set detail uses specified bedding sand | Often uses compatible smaller angular aggregate in a coordinated detail |
| Installation control | Moisture, lift placement and specified compaction | Placement and compaction suited to the specified aggregate and system |
| Design question | Support, stability and drainage | Support plus layer compatibility and, where applicable, reservoir function |
These are system distinctions, not claims that all dense-graded stone blocks water or all open-graded stone drains every site. Quarry gradations and complete details matter more than the shorthand names.
Permeable paving is a separate design commitment
CMHA PAV-TEC-018 describes permeable interlocking concrete pavement with coordinated joint, bedding and open-graded reservoir materials. Surface infiltration, water storage and discharge need assessment alongside traffic support.
Installing open-graded base below conventional tight-jointed pavers does not automatically make the surface permeable. A permeable system may infiltrate, use underdrains or include a liner depending on its design. Do not promise infiltration into an unsuitable subgrade merely because the base has void space.
Prevent unintended particle migration
Check the interface between fine bedding and coarse base. Without compatible grading or a specified separation detail, smaller particles can move into larger voids and change layer support. A geotextile added casually at that interface is not proof that the resulting assembly will perform.
Also check the subgrade/base interface, restraint support and transitions to existing paving. A material change at one layer affects more than the material delivery line.
Do not use the same purchasing conversion for both
The same area and thickness produce the same geometric layer volume. They need not produce the same mass or delivered quantity for different aggregates. Obtain density and any loose-to-installed relationship for the selected material; do not carry a previous dense-graded estimate’s ton-per-yard value into an open-graded order.
If the system has separate bedding, base and subbase reservoir layers, calculate each area and thickness separately. Adding all thicknesses into one order loses the material distinctions.
Make the selection with the site detail
Ask which published assembly or project specification applies, how water leaves it, which gradations are required and how installation will be verified. A project with slow-draining soil requires a water-management answer whichever grading is chosen. The material selection guide provides supplier questions; base depth addresses structural selection.
Use the Paver Base Calculator for each specified aggregate layer. Enter the selected footprint and compacted depth, then use that material’s supplier density if ordering by weight.
Sources and scope
- ASTM InternationalStandard Specification for Graded Aggregate Material for Bases or Subbases for Highways or Airports
Graded aggregate material specification. Does not establish a universal base depth or density.
- CMHACMHA PAV-TEC-002 (formerly Tech Spec 2 / Tech Note 2): Construction of Interlocking Concrete Pavements
Conventional interlocking concrete pavement construction; scoped base minimums and nominal uncompacted bedding guidance.
- CMHAConstruction of Permeable Interlocking Concrete Pavement Systems — PAV-TEC-018
Open-graded bedding, base and reservoir construction in permeable systems; not a substitute conventional sand-set detail.
Material specifications, construction guidance and product instructions have different scopes. Example inputs demonstrate calculations; they are not project defaults.