5.5.4 Other Seals
Strain alleviating membrane interlayer (SAMI)
SAMI treatments use highly modified binders and are applied at high rates of application. SAMI treatments are usually designed to be overlaid with asphalt within 1 day (2 days maximum) after construction. If they are left for a longer period under traffic, they should be designed as a SAM treatment to reduce the risk of flushing or bleeding.
As a SAMI is trafficked for only a short period, or not at all, the normal basic voids factors and adjustments do not apply. A design voids factor (VF) of between 0.16 and 0.18 is generally suitable, with VF = 0.17 appropriate for most designs. The lower or higher value may be adopted considering the volume and type of traffic the SAMI will be exposed to during its short life.
Design binder application rate is calculated by Equation 4:
|SAMI design binder application rate = (0.17 × ALD × BF) + allowances (rounded to nearest 0.1 L/m2)||4|
|ALD||=||Average least dimension (Section 5.3)|
|BF||=||Binder factor (Section 6.3)|
For a SAMI treatment to provide effective crack reflection performance, a minimum design binder application rate of 1.8 L/m² is recommended.
This minimum binder application rate can generally be achieved with a 10 mm single/single seal, but 14 mm aggregate may be used where higher binder application rates are required to control more severe cracking, or when being placed as a waterproofing layer under open graded asphalt.
Geotextile reinforced seals (GRS)
A minimum fabric mass of 130 g/m2 is used for general sealing applications with 10 mm aggregate. Aggregates larger than 14 mm have an increased potential for puncturing the fabric, particularly when used as an initial treatment over a soft base, and heavier grades of fabric (175 to 200 g/m2) are preferred for such applications.
Geotextiles made from polyester are preferred when using hot bitumen as they have a higher melting point. Where polypropylene fabric is used, the binder temperature should not exceed 170 °C.
GRS (seals or reseals) are designed in accordance with conventional design procedures for the relevant seal type (single/single or double/double) and binder type. Allowances are then added for binder retention by fabric as follows:
- Determine design binder application rate, Bd, for the relevant seal type overlying the geotextile (Section 5.5.1 or Section 5.5.2).
- Determine binder geotextile fabric retention allowance (Section 6.5.1).
- Calculate the design binder application rate for GRS, BdG (Bd + geotextile fabric retention allowance).
- Apportion BdG between the bond coat allowance (Section 6.5.2) and seal coat binder.
- Determine aggregate spread rate for GRS by design of the relevant seal type (Section 6.7) with no further allowances.
Fibre reinforced seals (FRS)
The design of FRS is based on conventional single/single design procedures, including allowances for polymer and bitumen emulsion, plus an appropriate allowance for the amount of binder required to coat the fibres. The procedure is as follows:
- Determine design binder application rate, Bd, as for a single/single seal (Section 5.5.1).
- Determine glass fibre binder allowance (Table 6.7).
- Calculate the design binder application rate for FRS, BdF (Bd + glass fibre binder allowance).
- Determine aggregate spread rate for FRS as for conventional single/single seal with bitumen emulsion binder (Section 6.7.3) with no further allowances.
- A scatter coat of a small sized aggregate is generally applied to 10 mm and 14 mm aggregate FRS. The scatter coat is usually applied at a rate of 400 to 600 m2/m3 using 7 or 5 mm aggregate on 14 mm seals, and 5 mm aggregate on 10 mm seals.