Installing control joints is nothing new. But in recent years there have been debates among concrete professionals over the best methods and materials to properly fill control joints.
Owners want to move projects along as quickly as possible and there is always pressure to cut costs and save money. Enter polyurea to the joint filler market in the mid-1990s. The physical characteristics and installation advantages of this material solved this quicker, less expensive, faster goal. But as with any new technology there were assumed benefits and, after some time in the field, there were, and are, actual benefits.
Claims were made by some manufacturers that polyurea could be used on green concrete. Other recommended installation techniques sometimes resulted in joint sealers being installed too early. Joints were also sometimes sealed in ways that minimized the amount of sealant in order to save money. These practices resulted in as many failures as successes.
A new joint sealer/filler technology with real advantages was upon us. And now that the mythical recommendations and the actual proven techniques have converged, joints have a clear winner. To fully understand the life-cycle impact of polyurea joint fillers, let’s first look at the life of a concrete control joint.
The rugged life of a control joint
As we know, control joints (more properly, according to the American Concrete Institute, contraction joints) are essentially planned cracks that allow for movements caused by temperature and moisture changes (drying shrinkage). In other words, when the concrete does shrink and crack, the control joint is placed so that the slab will crack on a line instead of randomly across the slab. A slab will continue to shrink, and widen the control joint, for years, although most of the shrinkage takes place within the first year and especially within the first 90 days.
Once the joint is cut into place, the joint itself is ready to do its job. The joint can then be left as is, sealed, or filled. Sealing or filling should be put off as long as possible to allow the joint to widen, although in practice joints are usually sealed or filled sooner than ideal. Understanding the difference and the purpose of sealing or filling is important. Sealing is done with a flexible (elastomeric) material typically installed over backer rod to give the seal the proper shape in the joint. Filling is done the full depth of the joint with a material that has enough compressive strength to support the edges of the joint from stresses imposed by heavy, hard-wheeled traffic. Joints in slabs that will not be subjected to heavy hard-wheeled traffic can safely be left unfilled or sealed with a flexible sealer.
But if left unsealed or unfilled, control joints can become areas for dirt, dust, and debris to collect and cause problems. In food processing, pharmaceutical, and medical facilities, they can become even greater problem areas harboring water, moisture, and threatening bacteria if not properly filled and maintained.
Failure to properly seal or fill control joints may also result in moisture migrating through the joint into the base and subbase and incompressible debris filling the joint, impacting adjacent slab sections. When that happens, consequent base/subbase and slab distress can result in rocking slabs and even vertical displacement at the joint.