Prime Coat/Granular Sealing

Prime Coat/Granular Sealing

A prime coat is a single application of either a specially formulated asphalt emulsion or a low-viscosity asphalt cutback. Their primary functions are to penetrate quickly into the granular surface and bind the material together, to partially waterproof the granular surface to prevent water erosion, to provide a temporary riding surface prior to overlay or seal coating and to provide a bond between the existing surface and the new wearing surface.

The asphalt emulsions used as prime coats typically contain a combination of asphalt and specially engineered agents to aid in penetrating the granular surface, while binding the aggregate particles to achieve stabilization.

Design Criteria

In order to satisfy the prime coat function some emulsion or cutback must penetrate into the base. The tightness of the granular surface can influence the degree of emulsion dilution needed. The type and the gradation of aggregate will require adjustments to the quantity of prime coat needed. If the surface is very hard it may be necessary to loosen the surface by scarifying prior to spraying. Damping the surface will help to allow for penetration. If ponding develops a blotter sand may be required to absorb the free standing emulsion or asphalt cutback.

Materials

Asphalt Emulsions:

The asphalt emulsions used as prime coats typically contain a combination of asphalt and special penetrating agents to aid in penetrating the granular surface, while binding the aggregate particles to achieve stabilization. Products such as Enviro-Prem or EDL can be used for this purpose.Cutback

Cutback Asphalt:

The cutback asphalt used as a prime coat is a low viscosity asphalt containing a high quantity of solvent. The solvent allows the asphalt to penetrate into the granular and then evaporates out to leave the asphalt residue. RC 30 or Primer are used as prime coats.

Performance Guidelines

In order to construct a proper well designed prime coat the following guidelines should be followed:

  • Determine the type of prime coat to be used. Emulsion or cutback
  • Evaluate the road surface to be primed
  • Determine the dilution rate of the emulsion
  • Determine if scarification is needed
  • Calibrate and inspect all equipment
  • Follow proper construction techniques
  • More than one application of dilute emulsion may be needed
  • A sand blotter may be needed
  • Use traffic control to protect seal
  • Work only in weather suitable for type and grade of emulsion being used

Related Resources

DescriptionPdf File
Canadian Investigation of Flexible Pavement DesignRESEARCH
A Design of Bituminous Mixtures with Curved Mohr EnvelopesRESEARCH
Designing Standard Asphalt Paving Mixtures for Greater DurabilityRESEARCH
Determination of Factors Affecting Shear Testing Performance of Emulsion Tack CoatsRESEARCH
Development of Stone Mastic Asphalt for Ontario UseRESEARCH
Flexible Pavement Thickness RequirementsRESEARCH
Intro of Stone Mastic Asphalt (SMA) in OntarioRESEARCH
Particle Index Evaluation of Aggregates for Asphalt MixturesRESEARCH
Rational Design of Bituminous Paving Mixtures with Curved Mohr EnvelopesRESEARCH
A Rational Method of Design for Bituminous Paving MixturesRESEARCH
Solvent free Bitumen Emulsion for Prime Coats and Granular SealingRESEARCH
Some Applications of the Elastic Theory Approach to the Structural Design of Flexible PavementsRESEARCH
Thickness Design for Flexible PavementsRESEARCH
An Ultimate Strength Approach to Flexible Pavement DesignRESEARCH
Bio-Solvents in the Production of Emulsified Prime Coat SystemsRESEARCH
Product Data Sheet – CHP-2mPDS
Product Data Sheet – CHP-2mPPDS
Product Data Sheet – CHP-2rPDS
Product Data Sheet – CHP-2rPPDS
Product Data Sheet – Enviro-PremPDS
Prime Coat/Granular Sealing – PDOTECH
Product Data Sheet – Colasphalt PrimePDS
Product Data Sheet – EP-2000 APDS
Product Data Sheet – EP-2000 BPDS

October 2020
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