Cracks and Joints: Controlling Concrete Pavements
By: Jordan Wilkinson, PLA, Landscape Architect at DG2 Design Landscape Architecture
(Figure 1 Cracked Concrete Sidewalk – Source: troweltrades.com)
Concrete will always crack, it’s inevitable. As Landscape Architects one of our primary focuses is the design of hardscapes, which often includes ridged pavements such as poured concrete. Concrete joints are a relatively minor part of most projects, but can easily reveal poor planning and design if installed incorrectly.
To avoid unwanted cracks, designers utilize a few basic concepts: control joints, and expansion joints. Control joints are installed in concrete to provide weaker areas (thinner) in an attempt to induce cracks where they are wanted. This is achieved by either tooling or sawing a groove in the concrete approximately ¼ of the overall depth of the pavement. The idea being that if control joints are used properly, concrete pavement will only crack at these pre-planned locations, and thus will not really be visible or create unsightly pavement. Of course, there are many variables that can cause concrete to crack unevenly, and the use of control joints is only one mechanism that designers use to control cracking. For a typical linear sidewalk or path, control joints may be installed every 4’ to 6’ feet along the path of travel. The dimension between control joints depends mostly on the width of pavement, and a good rule of thumb to remember is to place control joints in a manner that will break the pavement up into squares. Uniform segments provide uniform cracks. Larger pavement areas such as plazas, patios, or driveways can be divided into larger segments in the range of 6’ to 12’ feet square.
(Figure 2 Expansion Joints Layed Out in the Field – Source: DG2 Design)
Another type of joint used by designers is what is commonly called an isolation or expansion joint. These joints are created by the use of concrete forms or boards that separate portions of concrete from each other entirely. Expansion joints are full depth, so that large pieces of pavement can expand and contract independently of each other without cracking. The gap created by an expansion joint is typically filled with a flexible filler and sealed with a rubberized caulk. In most typical linear sidewalk applications, expansion joints can be placed every 15’ to 30’. Expansion joints are also utilized to separate concrete pours from buildings, foundations, walls or other structures. A separation of these structures ensures that they will move independently and not crack.
While most concrete joints provide a very important structural purpose, they can also become an aesthetic element in a project’s overall design. While there are certain guidelines and rules of thumb for laying out concrete joints, there is a great deal of flexibility allowed that can be used to create thoughtful patterns in the pavement. One question we might ask ourselves as Landscape Architects is, “Do I want this pavement to be noticed or not?” A creative joint pattern that compliments its context can be very pleasing to the eye, but poorly planned joints can be even more noticeable and even distracting. I am a strong believer in simplicity when it comes to concrete joint layout. This approach may include beginning an even distribution of control joints at the corner of an adjacent structure and dividing the joint spacing evenly to align with another critical control point in the ground plane.
(Figure 3 Saw-cut Control Joints Properly Installed – Source: DG2 Design)