Table of Contents

6.7.3 Single/single Seals

The design aggregate spread rates for single/single seals to produce a satisfactory aggregate mosaic are shown in Table 6.8.

To achieve a satisfactory mosaic and to avoid binder pick-up using low viscosity binders and emulsion binders, the aggregate spread rate needs to be heavier than for other binders.

Table 6.8: Aggregate spread rates for single/single seals

BinderAggregate spread rate
C170, C240, C320, multigrade bitumen, PMB900/ALD
Emulsion, AMC4 & AMC5 cutback binders800/ALD

Table 6.9 provides the aggregate spread rate for a scatter coat of small-sized aggregate. A scatter coat is sometimes used with single/single seals to reduce the risk of aggregates being dislodged by traffic during initial trafficking. It is particularly useful when using emulsion binders to overcome the low cohesion during the curing period.

Table 6.9: Aggregate spread rates for scatter coat

ApplicationAggregate spread rate
Scatter coat400

For strain alleviating membrane interlayers (SAMI), the aggregate spread rate needs to be lighter than for conventional bitumen and multigrade binders to enable interlock between the seal and the overlying asphalt mix (Table 6.10).

Table 6.10: Aggregate spread rates for SAMI

ApplicationAggregate spread rate
SAMI1000/ALD to 1100/ALD