PROPER USE OF ISOLATION AND EXPANSION JOINTS IN CONCRETE PAVEMENTS

Isolation and expansion joints accommodate anticipated differential horizontal and vertical movements that occur between a pavement and a structure. Their purpose is to allow movement without damaging adjacent structures. Contraction or control joints also absorb some movement; however, their main function is to control the location and geometry of the natural cracking pattern in the concrete slab. Because pavement performance can be significantly affected by the planned use and location of isolation and expansion joints, care should be taken in their design. Though the terms are sometimes used interchangeably, isolation joints are not expansion joints.

Isolation joints isolate the pavement from a structure, another paved area, or an immovable object.

Isolation joints include full-depth, full-width joints found at bridge abutments, intersections, or between old and new pavements. The term isolation joint also applies to joints around in-pavement structures such as drainage inlets, manholes, footings, and lighting structures.

Expansion joints are defined as full-depth, full-width joints placed at regular intervals of 50 to 500 ft (15 to 150m) (with contraction joints in between). This is an old practice that often caused joint pumping, spalling, and corner breaks. These joints are not needed and often create problems.

Good design and construction of contraction joints has virtually eliminated the need for expansion joints, except under special conditions. The improper use of expansion joints can lead to high construction and maintenance costs. By eliminating unnecessary expansion joints, failures are minimized and the pavement will provide better performance.

Pavement expansion joints are only needed when:

1. The pavement is divided into long panels (60 ft(18m) or more) without contraction joints in-between.

2. The pavement is constructed while ambient temperatures are below 40°F (4°C).

3. The contraction joints are allowed to be infiltrated by large incompressible materials.

4. The pavement is constructed of materials that in the past have shown high expansion characteristics.

In most situations, these criteria do not apply. Therefore, expansion joints should not normally be used.