There is a long history of using expansion joints in concrete for various reasons. The primary thought is to allow for future thermal expansion of the paved surface while minimizing stress buildup, potential cracking, and possible blowups in hot weather. However, with proper design of the concrete pavement, along with good construction practices and adequate maintenance, concrete does NOT need expansion joints at regular intervals throughout the paved area.
Expansion (or isolation) joints are recommended to be used to isolate different concrete elements or other structural items that abut one another, such as intersecting pavements, inlets, manholes, light poles or bollards, or sidewalk against curb & gutter.
Concrete pavements and slabs on grade require contraction or control joints, to force the concrete to crack at those planned locations during the natural drying shrinkage that starts to occur within the first few hours of the concrete placement. That shrinkage is typically around 0.75 inches for every 100 feet of concrete placed. Therefore, for a 5-foot joint spacing that is typical for concrete sidewalk, that natural shrinkage would cause each joint to open up 0.0375 inches.
If those joints are sealed (like most new concrete roadway and airfield pavements), the joints won’t fill up with incompressibles during cold weather. Therefore, those joints will be able to properly close during hot weather, and there will be room for that expansion at each sealed contraction joint. The formula for change in length of a concrete slab is as follows:
Therefore, we would expect the expansion due to temperature of our 5-foot sidewalk slab to be approximately 0.0288 inches, given:
Most sidewalks do not utilize joint sealants at tooled or sawn control joints. Therefore, expansion joints might be preferred to allow for the growth of the sidewalk over time, due to the joints filling up with dust, sand, pebbles, etc.
We have seen the use of ½” expansion material work very well in the field, and this flexible foam material is often preferred over the 1-inch asphalt-fiberboard that is typically used, as the foam is hydrophobic and does not grow organic material as easily. Being flexible, it also works well for curved areas and is easier for field personnel to cut and affix in place.
Guidance from the American Concrete Institute (ACI PRC-224.3-95: Joints in Concrete Construction) says that “the expansion of concrete slabs on grade is generally less than the initial shrinkage, and provision for expansion is seldom required.” Regarding the regular use of expansion joints, the guide also states “expansion joints in pavements are needed only in very unusual conditions of construction or with unusual materials.”
If expansion joints are utilized for your project, regardless of the expansion material used, it MUST fully separate the concrete on either side of the joint. There should be no gaps or holes in the material – there should be no concrete-on-concrete contact across the expansion joint area. And if dowels are used to maintain load transfer across the joint, they must be smooth (not deformed rebar) and have expansion caps, with gaps inside that match the expansion joint thickness.
