Plan your concrete project to withstand cracking
From the Panama Canal to the Pentagon to driveways and buildings worldwide, concrete is the most popular building material. Strong and durable, with the ability to resist erosion, fire, and rotting, it’s also one of the most long-lasting building materials there is.
On the other hand, concrete is an inflexible material prone to cracking. Thankfully, different types of joints can help reinforce concrete’s sturdiness and help to avoid cracking. Keep reading to learn the differences between concrete expansion joints and control joints and how both can benefit your concrete project.
The purpose of control joints
Since concrete is made of a mixture of cement, aggregate, and water, water evaporation is natural during the curing process. This loss of water compresses the concrete mixture leading to shrinkage. And when the concrete material shrinks, it creates tensile stress on the surface, leading to cracking as it dries.
Control joints, also known as contraction joints, help to avoid surface cracking by ensuring that the cracking due to shrinkage occurs beneath the surface of the concrete rather than on the surface. In other words, control joints help manage cracking so that the surface remains smooth and aesthetically pleasing while cracking happens out of sight.
When to execute control joints
Joint spacing is planned before pouring concrete and executed after the concrete is poured — but before the concrete has fully hardened. Control joints should be cut between 6 to 18 hours after pouring, depending on the weather conditions and the concrete mix. Using a concrete saw, straight lines are cut into the partially hardened concrete.
Control joints should be cut at least a quarter of the depth of the slab and at regular intervals about 30 times the thickness of the slab.
The purpose of expansion joints
Concrete expansion joints, also known as movement joints, allow the concrete to move without putting pressure on the other structures it borders. The expansion joints are filled with a flexible sealant or joint filler that can absorb the pressure of movement. This allows for shifting without causing severe stress that leads to fracturing.
For example, a concrete slab or concrete driveway that abuts a building or other concrete slab will have planned expansion joints. The sealant that fills the expansion joints is pliable, allowing for movement and shifting caused by things like:
- Temperature changes
- Thermal expansion
The sealant also acts as a type of waterproofing to protect the concrete from moisture and other elements.
When to execute expansion joints
Expansion joint systems are planned before pouring concrete. Rather than cutting into the concrete like control joints, expansion joints are full-depth gaps between each concrete slab or between buildings and other structures. As such, expansion joints are spaced before pouring and can be poured on different days — offering a good stopping point for the end of the day.
Control joints vs. expansion joints
So, which type of joint should you use in your concrete pouring project? Well, both! Since each has its unique purpose in helping avoid cracking from different causes, most large concrete projects use control and expansion joints. Using both types of joints can extend the longevity and durability of your concrete and avoid costly repairs or replacements down the line.
Washington’s concrete-cutting experts
Ready to hire a professional for your concrete cutting project? Look no further than our trusted experts at Cascade Concrete Sawing & Drilling. We’ve been Washington State’s favorite concrete cutters for residential and commercial projects since 1980. Let’s get started — contact us for a free estimate today!