6.5.1 Binder Fabric Retention Allowance
A binder fabric retention allowance is added to the preliminary design binder application rate for binder required to saturate the fabric. The extent of the binder retention allowance varies from 0.9 to 1.3 L/m2 of residual binder, depending on the thickness and characteristics of the geotextile fabric and type of binder being used.
This allowance is apportioned between the bond coat and the first application of binder in the seal coat.
Where possible, the allowance for retention of the binder by fabric should be calculated using an appropriate test procedure (ASTM 2005) with the following modifications:
- C170 bitumen is used as the binder
- testing is undertaken at 160 °C.
This covers:
- material thickness (mm) under 2 kPa pressure (AS 3706.1)
- unit mass (g/m2) of fabric (unprocessed material)
- unit mass (g/m2) of fabric (processed material).
Typical allowances for binder retention are shown in Table 6.6.
Table 6.6: Typical binder retention allowance for geotextile reinforced seals
| Geotextile grade | Retention allowance (L/m2) |
|---|---|
| 130 to 140 g/m2 | 0.9 to 1.0 |
| 175 to 200 g/m2 | 1.1 to 1.3 |