An expansion joint is a deliberate gap built into or between concrete slabs that allows the concrete to expand, contract, and move with temperature and moisture changes without cracking.
In depth
Concrete expands in heat and contracts in cold. Expansion and control joints give it planned places to move so stress relieves at the joint instead of cracking the slab randomly. But an open or failed joint is also a pathway for water to reach the soil beneath, where it washes out the base and undermines support.
Keeping joints sealed is therefore part of protecting a slab from settlement. After raising, sealing joints and gaps is a standard step to keep water from re-eroding the newly stabilized base.
How Acme applies it. Acme recommends applying caulk to gaps and expansion joints after raising to prevent water seepage under the slab, part of the water management that prolongs the life of a repair.
Related terms: Joint Sealing, Soil Washout, Concrete Cracking, Grading & Drainage
Frequently asked questions
What is an expansion joint for?
It gives concrete a planned place to expand and contract so movement relieves at the joint rather than cracking the slab.
Why do expansion joints need to be sealed?
An open joint lets water reach the soil beneath the slab, washing out the base and causing settlement. Sealing joints keeps water out and protects support.