Screening Aggregates

PER CALTRANS SECTION 37

Screening aggregates shall consist of broken stone, crushed gravel, or both. At least 90 percent by weight of the screenings shall consist of crushed particles as determined by California Test 205.

Screenings shall be clean and free from dirt and other deleterious substances.

The percentage composition by weight of screenings shall conform to one of the following gradings:

The following are guidelines for asphaltic emulsion spread rates measured in gallons per square yard. The emulsions typically used in screenings projects (chip seals) are of the RS (rapid set) classification.

PLACEMENT GUIDELINES
Proper surface preparation prior to placement of screenings is important to the success of the project. The surface should be swept or rinsed with water and allowed to dry prior to placement.

Surface treatments requiring asphalt emulsions should not be done during cold or wet weather. Guidelines recommend temperatures of at least 50 degrees and rising, the road surface should be 80 degrees before an application of emulsified asphalt is applied for chip seals. Emulsions applied at lower temperatures may not break or cure properly. Without proper cure the asphalt will not hold the screening aggregates.

The proper equipment is essential to a quality chip seal surface treatment. This includes a Distributor Truck or Spray Pot for small jobs, chip spreader, and rubber tire or pneumatic roller.

Adhering to these guidelines will help to prevent the most common chip seal failures.

Caltrans Specification Screenings Aggregates are available at the A.R. Wilson Quarry in Aromas. For more information please contact Don Barrett in the Aggregate Sales Department at 831.768.2309, fax 831.768.2401 or send e-mail todbarrett@graniterock.com.

Guidelines for Asphaltic Emulsion spread rates measured in gallons per square yard

Chip Seal Types Range of Gallons Per Square Yard
Fine 0.15 to 0.30
Medium Fine 0.25 to 0.35
Medium 0.25 to 0.40
Coarse 0.30 to 0.40
Double Coat Applications
1st Application 0.20 to 0.35
2nd Application 0.20 to 0.30

Percentage Passing

Sieve Sizes Coarse ½″ × #4 Medium 3⁄8″ × #6 Medium Fine 5⁄16″ × #8 Fine ¼″ × #10
¾″ 100
½″ 95-100 100
3⁄8″ 50-80 90-100 100 100
No. 4 0-15 5-30 30-60 60-85
No. 8 0-5 0-10 0-15 0-25
No. 16 0-5 0-5 0-5
No. 30 0-3 0-3
No. 200 0-2 0-2 0-2 0-2