4.5 Surface Applications
4.5.1 Prime Coat
1. The application rate of bitumen and percentage of cutback to be used shall be instructed by the Engineer on site.
2. The rate of spread of bituminous material for the prime coat shall be 1.0 litre per square meter with tolerance of 0.1 litre per square meter.
3. Prime coat would be applied only when the existing surface is dry or sufficiently low in moisture and assure uniform distribution of the bituminous material, when the atmospheric temperature is above 15ºC, and when the weather is not foggy or rainy or rain, in the opinion of the Engineer would be considered.
4.5.1.1 Preparation of Surface
1. The layer to be primed would be cleaned of all loose and deleterious material with air compressor without damaging to the pavement surface.
2. Scale, clay and other foreign material would be removed by hand where instructed.
3. Prime coat would be applied when the moisture content is satisfactory for full penetration as instructed by the Engineer.
4. In this manner, the surface would be prepared to expose a hard tight mosaic of large aggregate in the base course.
5. Before prime material is sprayed the layer to be primed would be checked for compliance with the surface and other requirements specified.
6. Sections not complying with the specification would be corrected and remedial measures would be taken to the satisfaction of the Engineer before priming.
4.5.1.2 Application of Prime Coat
1. Prime coat would be applied by means of a bitumen distributor for large areas and by lance and nozzles for small and inaccessible areas so as to achieve an even distribution of the prime coat over the surface.
2. At the start and end of each run approved material would be spread over the surface to ensure a clean joint between adjacent runs and to protect adjacent surfaces and also to permit the distributor to build up sufficient speed so that at the start of each run the distributor shall be traveling at the correct speed for the instructed application rate.
3. The distributor shall be functioning properly in accordance with the manufacture’s instructions with all spray nozzles functioning and delivering prime coat at the same evenly distributed rate.
4. The total width of primed surface shall be 300mm wider than the specified width of the final surfacing and the edges of the prime shall be parallel to the center line of the road.
5. The prime coat application rate would be achieved by two or more repeated applications when necessary to avoid flow of prime coat on steep cross falls or gradients.
6. Any areas deemed by the Engineer to be deficient in prime coat after passage of the distributor shall be made good by spraying with a hand lance.
7. Road furniture such as kerbs, post boxes, sidewalks, utility poles, manhole covers etc would be protected from prime coat spray with adhesive paper.
8. The spraying temperatures for prime coat would be as technical specification.
4.5.1.3 After Care
1. Following the prime coat application, the primed surface would be allowed to cure for a minimum of 24 hrs without being disturbed so as to allow the prime coat to penetrate the surface fully unless full penetration and curing has taken place in a shorter period.
2. As soon as the primed surface has cured sufficiently, the road where practicable, be opened to public traffic for a period of 14 days or less if agreed by the Engineer.
3. During this period the primed area under traffic would be maintained and all damaged caused by traffic would be repaired as instructed by the Engineer.
4.5.2 Tack Coat
4.5.2.1 General
This work would consist of an application of a tack coat to an existing pavement prior to construction of a surfacing so as to provide a bond between the two layers.
4.5.2.2 Weather Limitations
The tack coat would be applied in dry weather and when the ambient temperature is not below 15ºC and it would not be applied when rain is imminent.
4.5.2.3 Preparation of Surface
1. Prior to application of the tack coat, the surface would be dried thoroughly swept and rendered clean of clay, dust and any other extraneous material.
2. The tack coat would be applied when the surface is dry.
4.5.2.4 Application
1. This would be applied at ambient temperatures and it would be warmed to facilitate uniform application, where necessary mechanical sprayer, hand sprayer or by any other means would be used for the application of the tack coat.
2. In areas being treated, precautions would be taken to prevent the surfaces of structures and trees being spattered or marred, and the binder getting into channels, catch pits and drains.
3. Tacked surfaces would be allowed to dry until the proper condition of tackiness is achieved to receive the surface course.
4. Until the surface course is placed, the tack coat would be protected from damage.
5. Tack coats would not be left applied for more than about 6 hrs without the placement of the surface course.