Asphalt Base Course

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Asphalt Base Course

What is Asphalt Base Course?

Asphalt Base Course, the lower structural layer of asphalt pavement providing load-bearing support for surface courses.

Description

The asphalt base course is a thick lift of dense, graded hot mix placed on a prepared subbase or aggregate base, designed to distribute traffic loads and resist shear. Typically containing larger aggregate (up to 1 inch) and higher asphalt content than surface mixes, base course thickness ranges from 3 to 6 inches, depending on traffic class. Compaction targets 92 to 96 percent of the maximum density, as measured by a nuclear gauge. After cooling, intermediate and surface courses bond to the base with a tack coat.

FAQs

  • When is an asphalt base required?

    For heavy traffic roads, parking lots, and areas with weak subgrade.

  • What aggregate size is used?

    Nominal maximum size 25 mm to 37.5 mm for higher stability.

  • How is thickness determined?

    Pavement design charts consider ESAL traffic and subgrade CBR.

  • What temperature is the base laid on?

    Between 275 and 300 Fahrenheit for workability.

  • Who tests base density?

    QA technicians using nuclear density gauges or cores.

  • Can the base course be left exposed?

    Temporarily, but the surface course should follow within 12 months.

  • Is tack coat applied between lifts?

    Yes, emulsified asphalt ensures the bond of subsequent layers.

Fun Fact

Fun Fact: Interstate Highway System design guidelines call for asphalt base layers capable of carrying 100 million equivalent single axle loads over 20 years.

CSI Code

32 12 16

NAHB Code

270