Contraction and Control Joint Repair

Concrete Repair Seminar: Why are my control joints spalling and what can I do to stop it?

Contraction joints (or control joints) are joints cut into a slab shortly after pouring. The purpose of these joints is to control the cracking of the slab as it cures. Most concrete slabs shrink and sometimes curl for the first 12 months after pouring. Contraction joints allow the slab to crack at predetermined intervals instead of natural random cracking. Joint filler is used to protect the joints from spalling and chipping caused by traffic on the slab.

 

As the slab cures for the first 12 months, it shrinks in size and may even curl up at the joints. The contraction joints will expand as the slab shrinks. This causes the joint filler to split apart or dis-bond from the sides of the joint leaving them exposed to traffic.

 

When loads are rolled over the joint. The force of the load has to transfer from the wheel, to the concrete, and to the base. If the slab is even slightly curled and the joint is expanded, the force of the load will impact on the joint causing cracking and spalling. You may even get stress cracking parallel to the joint. You can sometimes feel the uneven load transfer across the joint if you stand with one foot on either side of the joint and have someone else roll a heavy load across the joint.

 

Eventually, you get a spalled contraction joint. The joint filler has completely failed or is missing. Wheels go “thunk, thunk” every time they go over the joint. Productivity suffers, and the joint fills with dust and debris.

The best way to repair spalled contraction joints is to lock them back up with Roadware 10 Minute Concrete Mender™ Once the slab is 12 months old, the shrinkage and curling has finished. There is no longer a need for contraction joints. Now you can use Concrete mender™ and silica sand to bond the slab back together from the base all the way up to the top. This will stabilize the slab and allow for complete and even load transfer from the wheels all the way down to the base. Your contraction joint problems are solved.

 

See how its done here:

NOTES: Locking up contraction joints is recommended for interior controlled environment applications. Exterior applications may have different results. Always test a small section of large repair for compatibility.