Friday, February 10, 2012

Expansion joints give bridges room to breathe

Freeway bridges at traffic interchange
Bridge expansion joints allow concrete to expand and contract
without cracking.
When we blogged about quiet pavement back in December, we got a lot of comments

We received plenty of questions, too, which we’ll attempt to answer here on the blog in the coming weeks – starting with one on bridge expansion joints.

But, before we get to the question let’s first take a look at what bridge expansion joints are.

Basically, expansion joints help give bridges a little “breathing” room.

Bridges made of concrete are going to expand and contract slightly for a number of reasons, including temperature changes, shrinkage of the concrete, settlement, ice and even the weight of vehicles.

Bridge expansion joints are what allow the concrete to naturally expand and contract without cracking. The rubber expansion joints are placed at the end of a bridge where it meets up with the freeway. These connectors give the concrete just enough space to move and avoid concrete cracks.

When crews are building bridges and installing the expansion joints they’re able to embed them in the concrete and make the transition flush … drivers don’t notice they’re driving over anything.

But, when asphalt rubber is placed on that bridge and the adjoining freeway, crews can’t just pave right over the joint – they need to leave a little gap to allow for the expansion joint.

In these cases, some drivers might notice a little bump. It’s a little more noticeable in the winter months as the concrete contracts and the joint expands (the opposite happens in summer). This is where our question comes in … we were asked by one of our readers if anything can be done.

To seek out the answer we turned to Tim Wolfe, ADOT’s Phoenix Maintenance District Engineer for an explanation.

He said that on smaller expansion joints crews can weld steel plates on top of the expansion joint “opening” to make for a smoother transition. In some cases ADOT crews also will mill the asphalt rubber around the gap so it “feathers” off near the expansion joint.

However, on larger bridges there are wider joints meant for taking a lot of expansion. The only option there is to remove the joint and replace it with a new one that sits a little higher. That option is a very costly fix for something that’s not a structural or safety issue. Bridge structures are inspected by ADOT and if taken at the posted speed limit bridge expansion joints should not pose any sort of safety hazard.

ADOT continues to evaluate options to improve the quality of the riding surface.
Posted by Angela DeWelles   |  Labels:  


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