7.3.2 Initial Seals
Curing time
Initially, the binder should be allowed to cure, or thicken and increase in viscosity, or in the case of emulsions ‘break’ before any trafficking of the initial seal is allowed.
When cutback bitumen is used, the secondary treatment should not be applied until a reasonable period of curing has elapsed, as residual cutter oil can soften subsequent bituminous surfacings. The curing rate depends on binder grade, application rate and climatic conditions during the curing period. A minimum of six months of warm or hot weather is recommended, although 12 months may be beneficial in colder weather. The minimum curing period may be reduced to three months for relatively low cutter content initial seal binders (such as AMC7) when used in warm or hot conditions.
Initial seals constructed with bitumen emulsions may be covered with asphalt after only two to three days, however a period of three months is recommended before covering with a spray seal.
Expected lifespan
An initial seal can be expected to last between 3 to 24 months, depending on traffic level, aggregate size, and choice of binder. Under light traffic conditions, there is potential for initial seal lives to exceed these approximations.
The use of larger aggregate sizes, multiple layer seals and PMBs may also contribute to achieving longer life spans.