Otta Seal - Composition and Application

Composition and Application

Otta seal is formed by adding graded aggregate to a soft bituminous binding agent. The agent is usually emulsified asphalt. Bituminous binder application rates are between 1.9 liter (0.42 US gallon/yard2) and 2.4 liter/m2 (0.53 US gallon/yard2) – the value is dependent on aggregate gradation and type. Low quality, local aggregates are often used in Otta seal. The largest aggregate size used is between 13 and 25mm (0.5 and 1 inch). The aggregate can contain up to 10% fine gravels. Aggregate quantities are usually close to 27 kg/m2 (50 lbs/yard2). Otta seal is easily cured by blinding with sand because of its soft binders. The soft binders quickly coat the sand; This is not possible for seals with harder binders. Cutback bitumens in the viscosity range of MC3000 to MC800 are the most common binders used.

Otta seal is formed in the following procedure:

1. Remove dust and foreign objects from the base.
2. Add small amounts of water to the base to suppress dust.
3. Apply aggregate at a rate of 1.3 to 2.0 m3 to 100m2 (depending on the grading of the aggregate) of road surface.
4. Apply a hot binder at a rate of 1.6 to 1.9 liters/m2.
5. Flatten the Otta seal using a tired roller until aggregates are pressing up between aggregate particles. This usually has to be done multiple times, typically several days after the first flattening.
6. For the first two to three weeks, allow traffic at low speeds to assist with further kneading. Aggregates will be dislodged by traffic and they should be broomed back onto the seal.