Q.: I have been contracted to build 2,000 linear feet of 5-foot-wide, 4-inch-thick sidewalk on a 4-inch gravel base. The specifications call for expansion joints every 20 feet. I contend that expansion joints are needed at a minimum of every 50 feet and where the walk will abut existing structures. Control joints will be cut every 5 feet. Am I right in suggesting expansion joints every 50 feet?
A.: According to several industry sources, expansion joints, even at 50-foot intervals, are not necessary for the sidewalk project. Long stretches of concrete do not require intermediate expansion joints. Proper use of contraction joints at short spacings of 5 feet will allow for proper movement of the individual sidewalk slabs. Due to normal shrinkage of the concrete after placement, the slab probably will never expand and become larger than it is at the time of placement.
Isolation joints, however, will be needed where the walk will abut existing structures. According to ACI 332, "Guide to Residential Cast-in-place Concrete Construction," isolation joints, sometimes called expansion joints, are only necessary to separate the sidewalk from a fixed or different concrete structure. Examples include separating the sidewalk from lamp posts, hydrants, footings, buildings, driveways, and curbs.
In response to a Problem Clinic question in the January 1995 issue of Concrete Construction regarding the need for expansion joints in sidewalks, we said that sidewalks do not require expansion joints if properly spaced contraction joints are used. However, Bob Banka of Mid-South Concrete Path Paving, Kingston Springs, Tenn., has run into problems with golf cart paths buckling when only contraction joints are used. Here's his solution:
From our experience installing golf cart paths, which are basically long sidewalks, we have found that we need to install fiber expansion board material about every 250 feet. Before we started this practice, we had a few occasions where our cart paths would buckle during hot summer days. Sometimes the concrete would rise 6 inches.
We tool our joints 1 inch deep every 6 or 8 feet, depending on the width of the cart path. Sometimes a panel would rise and crack at the joint, and sometimes, as the photo shows, it would crack midpanel. The problem seems to affect our cart paths placed on sandy soil or in areas that have a high water table.
To be safe, we now install 1 inch of fiber expansion board material with three dowels (one in the center and the other two about 6 inches from each edge of the path). Since we started this practice, we have eliminated the buckling.
We are not sure why the concrete would sometimes buckle. The only reason we have been able to come up with is that the fiber reinforcement we use holds the joints together so tightly, it does not allow the slabs to move independently.