4.2. Item 301 Bituminous Prime Coat

Prime Coat is an application of thin bituminous material to a porous base before putting on a surface course.

  • serve to stabilize the base material.
  • serve to plug the capillary voids in the pavement.
  • applied only to dry or slightly moist surfaces.

The following is a list of bituminous material used for prime coats considering the condition of the soil base and the climate:

  • In moderate and warm climates, use MC-70.
  • In cold climates, use RS asphalt cutbacks such as RC-70 or RC-250.
  • In very cold climates, eliminate the prime coat because the curing process may be extremely slow.
  • On densely graded base courses, use MC-30.
  • On loosely bonded, fine-grained soils, such as well-graded sand, use MC-70 or SC-70.
  • On coarse-grained sandy soils, use MC-250 or SC-250.

Material Requirements

Bituminous material shall either be Rapid Curing (RC) or Medium Curing (MC) Cut-back Asphalt, whichever is called for in the Bill of Quantities (Refer to the requirements of Item 702 –Bituminous Materials).

Range of Temperature:

Temperature Range = 32oC (min.) to 68oC (max.)

Required Minimum Testing Requirements:

Tests: 1 – Q, Quality Test for every 40 tons or 200 drums

Equipment Requirements

  • Self-powered pressure asphalt distributor
  • Power broom or other mechanical sweeping equipment
  • Water sprinkler
  • Armored Thermometer

Construction Procedure

  1. Prior to the application of the prime coat, check the base if it conforms with the required specifications.
  2. Apply the prime coat by using pressure distributor at a rate of 1 to 2 liters per square meter.
  3. Prime coat shall be left undisturbed for a period of at least 24 hours.
  4. Extend the prime coat at least 30 cm. beyond the edge of the surface on each side.
  5. Observed the time of penetration starting from the time of its application.