There is nothing new about installing control joints. However, concrete professionals have been debating the most appropriate methods and materials for filling control joints in recent years.
There is always a pressure to cut costs and save money, and owners want projects to move along as quickly as possible. The mid-1990s saw the introduction of polyurea to the joint filler market. Due to its physical properties and ease of installation, the material was able to accomplish this goal faster, less expensive, and cheaper. However, as with any new technology, benefits were assumed and, after some time in use, real benefits emerged.
The manufacturers cited the possibility of using polyurea on green concrete. Joint sealers were sometimes installed too early if other recommended installation techniques were used. The amount of sealant was sometimes minimized by applying the sealant in a manner that minimized the amount of material. However, these methods failed more often than they succeeded.
A new technology of joint sealer/filler with real benefits was on the way. Joints now enjoy an advantage thanks to the combination of mythical recommendations and proven methods. Let's examine the life of a concrete control joint first in order to understand the impact of polyurea joint fillers.
Control joints have a rugged life Control joints are cracks that allow movement in response to changes in temperature or moisture (drying shrinkage) as we all know (or should recognize) as contraction joints. The control joint is placed in order to prevent the slab from cracking on a line rather than randomly. Despite extensive shrinkage during the first year, and especially within the first 90 days, a slab continues to shrink and widen the control joint for years.
A joint is ready for use once it has been cut into place. Once that has been done, it can be sealed or filled. The joint should be allowed to widen before being sealed or filled, but in practice this isn't always the case. Sealing or filling has different purposes, so it is important to understand the differences. The seal is shaped in the joint using a flexible material (elastomeric) installed over a backer rod. A material is filled into the joints up to their full depth with enough compressive strength to support the edges from the stresses of heavy, hard-wheeled traffic. It is safe to leave joints in slabs unfilled or to use a flexible sealer for joints that will not be subjected to heavy wheeled traffic.
When control joints are left unsealed or unfilled, they can collect dirt, dust, and debris and cause problems. It can become even more of a problem if they are not properly filled and maintained, especially in food processing, pharmaceutical, and medical facilities.
When control joints are not properly sealed or filled, moisture may migrate through the joint and into the base and subbase, along with incompressible debris, harming adjacent slabs.
The result can be slabs that rock and even vertical displacement at the joints when the base/subbase is distressed.
Filling and protecting During the curing period of new slabs, the concrete joint and its filler material are subject to many stresses, and those stresses continue throughout its service life associated with shrinkage, thermal cycling, and traffic loads. Control joints of 1/8-to-3/16-inch width require serious protection after they are cut. Without support, these sharp edges can deteriorate quickly. or spalling, from traffic and slab movement during their service life. Joint fillers installed improperly can have a detrimental effect on the durability of the edges.
Joint fill material can be cracked or disbonded from joint edges when stressful forces pull it apart and compress it back together. Joint sealers and fillers can get damaged when they are pushed downward by traffic (punch-down forces).
Filling joints with polyurea Polyurea joint filler materials gained market share and popularity in the early- to mid-1990s, resulting in some debate over the proper technique to fill control joints. The traditional semi-rigid epoxies commonly used then have different physical properties than polyurea.
Polyurea was installed with a backer rod back then. With polyurea's better adhesion, faster set and cure times, greater elongation, and better adhesion than epoxy resin, the idea was to use less of it for a longer lasting bond and save money. Joint fill/joint protection cannot be achieved with the backer rod technique. With no full depth fill, the joint edge could split below the backer rod due to traffic load forces. When filled to the depth of the saw cut, joint edges are supported to the bottom.
Material such as polyurethane and silicone cannot withstand high traffic loads because of their low compression values. When these materials are not disbonded by punching down or accumulation of debris, they will seal joints against water intrusion. Backer rods are not edge protected. Materials and installation requirements differ for these sealants.
Physically, joint filler materials differ from joint sealants, as they have better strength and flexibility. They are designed to deal with compression problems. Epoxy offers good edge support and sealant properties when installed after most slab shrinkage has taken place. But shrinkage breaks the bond quickly with little elongation. It is important to fill these cracks.
In spite of shrinkage, polyurea remains bonded to the joint edges while serving as a sealant, regardless of its inability to support the joint edge. Applied as a joint filler, polyurea will elongate and crack when shrinkage is sufficient (polyurea will elongate about 10%). If polyurea is used in conjunction with epoxy, these voids should be filled with polyurea.
Also, polyurea is able to cure when moistened to varying degrees. Additionally, polyurea's better adhesion values create a myth. Polyurea was once sold as an installation method for green slabs. While polyurea can cure all by itself when moisture is present, in order for the material to adhere to the surrounding concrete, the surface in question must be dry. If the concrete is wet, adhesion is greatly reduced. In order to avoid spreading any polyurea or other material on wet surfaces, we do not recommend it.
As a filler and sealant for joints, polyurea has proven to be highly effective. Concrete, however, can move and deteriorate over time. For this reason, joints and joint fillers need to be inspected and maintained like any other building system.
Installation that is correct It is important not only to select the correct joint fill material, but also to adhere to the right surface preparation and installation techniques to avoid failure.
There are industry-recommended guidelines for the installation of control joints, joint fillers, and sealants thanks to organizations like ACI. It is recommended that control joints be positioned at least 1/4 of the slab thickness where joint placement will occur. This translates to control joints that are 11/2 inches deep for 6 inch slabs, 2 inches deep for 8 inch slabs, etc.
Tools and saw blades have been used to control the width of the control joint. In other words, with toled joints up to 2 inches deep, and with saw blades, the material is about 3/16 of an inch wide. It is necessary to clean out all control joints dry before filling with a diamond blade equipped with a vacuum attachment before filling. This removes latitude and debris. Surfaces that have been abraded must be clean, sound, and ready to apply joint filler. It is possible to widen a joint by an inch or two by using this procedure. A joint can be widened only by 1/8 inch to 3/16 inch with this procedure.
Prepare your joints properly at all times. Concrete shrinkage is the main cause of disbonding. Joint fill materials shrink as a result of shrinking concrete. Poor surface preparation can cause disbondment to occur faster.
Control joint formula for high performance: The use of polyurea in a control joint does not result in a reduction in lifecycle costs; however, there are many ways to demonstrate this. It is not recommended to apply polyurea to wet or green concrete, despite its ability to cure faster under a variety of conditions. Sealants and polyurea fillers can be used to improve the performance and lifespan of concrete control joints. In the right conditions, polyurea can endure years of use and endure even the toughest conditions.