What to do About Expansion Joints in Concrete

There’s some confusion about the correct treatment for expansion joints in concrete driveways, slabs, and larger construction such as roads or bridges. Expansion joints are full-depth gaps between individual poured-concrete slabs. The gaps allow the slabs to move with normal expansion and contraction or settling that occurs due to temperature changes or moisture conditions. If no expansion joints are planned in large runs of concrete, there is a tendency to form large cracks where the movement causes severe stress points in the concrete. That kind of crack will weaken the structure and may mean early replacement of the whole slab. That’s an expensive correction to an unnecessary problem.

Traditionally those gaps have been filled with flexible, asphalt-impregnated fiberboard strips to support the edges and keep incompressible debris from filling the gaps and restricting that necessary movement. This is very common in large construction such as roads and bridges, but also larger driveways, pool decks and sometimes sidewalks. This material needs to remain resilient and stand up to the pressure of the slab movement for the life of the slab itself. It generally does a good job, but may work its way out of the crack over time and need to be replaced. It also creates dark lines in the cracks that may be unsightly in residential applications such as driveways, patios and pool decks. Old installations of fiberboard can also hold moisture that could freeze/thaw in cold climates creating its own movement between the slabs.

Armacell makes a new expansion joint solution that will allow the concrete movement, keep out debris and is moisture resistant. OleTex® Expansion Joint Filler is made of closed-cell, cross-linked polyethylene which is completely waterproof, so it won’t swell or absorb water that might freeze in the winter. It’s semi-rigid, so it’s stiff enough to be used as a form or slide into joints easily, but unlike bulky fiberboard, it will follow curves with ease. OleTex filler strip is lightweight, sold in rolls of up to __ width and ___ thickness, and can be stored outside on the jobsite. Because it’s cross-linked it can be used with hot- or cold-pour sealants or with none at all. When it’s used without a sealant, the light gray color blends with the color of the concrete, making the joint almost invisible. For even more convenience, the filler strip is pre-slit with a ½” tear-off tab that can be left above the height of the wet concrete, then easily pulled away when dry to make a flush installation.

Armacell’s OleTex Expansion Joint Filler Benefits:

• Waterproof, Lightweight, Long-lasting
• No special installation method needed
• Won’t stain concrete
• Resists gas, oils, salts, acetone and other harsh chemicals
• Can be used as a concrete form
• Forms a bond-breaker to sealants
• Can be used with hot- or cold-pour sealants
• Complies with ASTM D 8139, and ASTM D 1751 for extrusion, compression recovery and water absorption as tested per ASTM test method D 545.
• Suitable for residential, commercial, municipal and Industrial applications

Expansion joints are often confused with control joints, which are the cuts made into a concrete pour that do not go all the way through the slab. They usually are less than an inch deep and are pressed into the surface of the concrete while it is still wet. These joints are common in driveways and are meant to force any small, hairline fractures to follow the control joint when the concrete contracts during the cure period. It keeps the cracks from being noticeable and they don’t affect the structure. Control crack do not need gap filler or sealant of any kind.

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