Is design of curbs part of problem?
There’s a pattern to recent snowplow damage to curbs built last year: Chunks have broken off at an “expansion joint,” a seam between the curb and sidewalk that’s part of the state’s design of roads here.
The concrete contractor who built the sidewalks – and others – say the joint is unnecessary and may be leading to increased damage.
Curbs are built into sidewalks without such a joint at several locations around town, including along municipal-owned Third Avenue.
“It’s a half-inch, head start on failure,” said Dave Stickler of Stickler Construction. Expansion joints weaken the integrity of the curb in several ways, Stickler said.
Water and soil that works its way into the gap weakens the joint, especially when grass starts sprouting there, Stickler said. Frequent freeze-thaw cycles that occur here in winter make the joints particularly vulnerable after water works its way in and expands after freezing, he said.
Also, a curb separated by a half-inch seam from the sidewalk is more susceptible to damage from plows than continuous concrete would be, Stickler said. “It allows snowplows to break it much easier. When a plow hits (the curb), (the joint) gives it room to expand for easy breakability. Concrete is made for compression, not expansion.”
Haines High School science teacher Mark Fontenot agrees. In terms of being struck by a plow blade or piece of equipment, a solid slab can absorb more force than a partitioned curb and sidewalk, Fontenot said.
Like Stickler, Fontenot said the parallel expansion joint isn’t necessary for shrinkage and expansion of concrete, citing the relatively narrow width of a sidewalk.
“The expansion is insignificant,” Stickler said.
Stickler said a better design would be to abut the sidewalk to the curb, which would leave just a crack called a “cold joint” – not a half-inch gap between the two. The top of that crack would be filled with caulk, which needs to be replaced from time to time, he said.
Despite local concerns, it doesn’t appear the state’s design of local curbs and sidewalk will be changing any time soon.
State Department of Transportation preconstruction engineer Pat Carroll said expansion joints are sealed to prevent intrusion of water, which can freeze and cause problems.
The joints also account for differential expansion of the sidewalk slab and the curb and gutter section, he said.
“We also believe that it is necessary to cast the sidewalk and curb separately for constructability reasons,” Carroll said via email. “You are suggesting that we should pour the sidewalk and curb and gutter as one single concrete pour. We foresee constructability concerns with this approach and most likely a crack will develop between the curb and the sidewalk.”