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Putting Expansion Joints In Concrete Drives

By: Chris Hogan MSc - Updated: 10 Apr 2017 | comments*Discuss
 
Expansion Joint Expansion Joints

A lot of people reading this will be thinking, "What, joints in concrete? Doesn't concrete just get poured out?" They'll be right, to an extent, but if you remember any really large, flat Concrete Surface you've seen, there will have been black lines across it every so often. Yes, those lines mark where the expansion joints are.

The Need For Expansion Joints

Concrete sets very hard, more so than many other popular drive surfaces. But like most materials it also expands and contracts as it heats up and cools down. Combine that strength with this expansion and it's easy to see why Concrete Cracks, and why you need to put in an expansion joint in a large slab.

There's aren't that many driveways that will need expansion joints. A slab can be about 20ft square (6m square) before it will need an expansion joint, but it's not only size that matters. As well as preventing the slab from simply pulling itself apart, expansion joints protect fittings, like drain access covers and adjacent walls, from being broken by the forces that the slab exerts as it expands and contracts.

Components Of An Expansion Joint

Expansion joints are gaps between sections of poured concrete filled with a material that allows movement in the gap (more on this later). The top edges of the two slabs will often be chamfered to prevent them from cracking (spalling) and one or both sides will have a recess for the top inch or two.

This recess is filled with a flexible sealant to prevent debris and water getting into the gap. It's this flexible cover that gives rise to the black lines, as traditionally this would have been bitumen. These days bitumen isn’t used so much and it's more common to employ a resin-based compound that's applied cold with a curing agent mixed in.

Filling The Gap

On a very large concrete surface dowelled joints are used. The steel dowels are inserted into one side of the joint with recesses in the opposing face. As the concrete expands and contracts the dowels slide in and out. The gap between the slabs will also be filled with a flexible material, often a board made of fibre.

It might seem odd filling a gap that's meant to allow movement, but the movement is small and slow. The board can cope with it as long as it is the right width for the gap, usually between 0.5-1.5in (about 1.5-4cm). The board prevents too much dirt and water getting into the gap which it inevitably would, even with the sealant at the top.

Get Expert Help For Your Drive

If this all sounds a bit complex, then that's because it is. Creating the right gap widths and filling them with the correct material is not really a job for the amateur. It's far better to get a contractor who can demonstrate that they have previously put expansion joints into a concrete drive.

If you are intent on laying a large or long concrete driveway yourself, you really should consult a structural engineer with the relevant experience before starting the project.

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