Asphalt Intermediate Course refers to an aggregate, sand, and asphalt cement mixture used as the intermediate, leveling, or scratch course placed in a lift between the asphalt/stone base and the surface course. Intermediate course is most commonly used in a roadway application, but is also used in driveways, parking lots, and sidewalks.
Asphalt intermediate course mixture typically includes smaller aggregate sizes than Base Courses of asphalt, but larger than surface courses. The most common aggregate composition for asphalt surface course meets the following gradations for amount of crushed limestone material passing through different size sieves:
100% passing 3/8″ sieve
90-100% passing 4.75mm sieve
65-100% passing 2.36mm sieve
40-85% passing 1.18mm sieve
20-60% passing 600micrometer sieve
7-40% passing 300micrometer sieve
0-20% passing 150micrometer sieve
0-10% passing 75 micrometer sieve.
The equipment required when placing Asphalt Intermediate Course will be an asphalt paving machine (or road widener paving machine for widening or trench repair) and 1-3 tandem rollers. The crew required will be 6-7 workers composed of the following: 3 operators for paver (one on top and 2 down low), 2 operators for rollers, and 1-2 laborers for hand raking and finish work.
Asphalt Intermediate Course can be done without a paving machine for smaller areas such as drives or small parking lots, but the production will reduce dramatically as the material will require hand or small equipment placement. Hand placement should be minimized (vs paver placement) if possible as it can lead to a rougher surface texture, segregation of the aggregate, and lessened compaction density. For wide open mainline roads with minimal traffic, peak productivity can be achieved. For widened sections, drives, and parking lots with twists, islands, turns, bumpouts, intersections, etc, productivity can be dramatically reduced as these areas require considerable handwork and starting/stopping/slowing of the paver.
A critical part of the road section assembly, asphalt intermediate course serves as the leveling, binding, or ‘scratch’ course prior to the placement of the surface course lift and requires a level, true longitudinal placement and often has a transverse cross slope from the crown of the road to the shoulder. For these reasons it will require a fair degree of horizontal, vertical, and aesthetic accuracy in preparation for the surface course. Bumps, low spots, and high spots can be somewhat compensated for in the surface course but the fewer imperfections there are in the intermediate, the easier the surface course can be placed with accuracy. Most engineers and localities will permit minimal amount of (commonly 0-35% of dry weight) RAP (Recycled Asphalt Product) in the mixture. RAP is considered not to perform and bind the mixture together as efficiently as new fresh asphalt binder.