Cutting concrete is essential to control cracking. All newly poured concrete shrinks slightly as it dries which can result in cracks. To control potential cracking the concrete is cut. These cuts are called Construction Cuts – also known as Control or Expansion Cuts.
Saw cuts are a used to create control joints in concrete, which help control where cracking occurs due to shrinkage. The cuts should be made at a predetermined spacing and only after the concrete has obtained sufficient strength but before internal cracking begins. Therefore, the timing of saw cuts is critical.
Timing is very important. Joints should be sawed as soon as the concrete will withstand the energy of sawing without raveling or dislodging aggregate particles. For most concrete mixtures, this means sawing should be completed within the first six to 18 hours and never delayed more than 24 hours.
Grooving to Control Cracking
Random cracking from shrinkage can occur in the period just after placement and before hardening. Finishers can “control” this random cracking by placing grooves in the hardening concrete to help release the stress from shrinking.
Without these spaces, in time, cracks could lead to the destruction of the concrete surface. Concrete contractors include these lines when they pour concrete to control and prevent these unpredictable cracks. Concrete will expand and contract over time, through drying, shrinking, moving, and bearing weight.
If you're using concrete to make a sidewalk, the shrinking concrete will cause cracks to appear as it dries. To prevent sidewalks from cracking in random spots and breaking apart, builders make lines in sidewalks. Of course, they don't just call them lines. The technical term for sidewalk lines is contraction joints.
The gaps allow the slabs to move with normal expansion, 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 significant cracks where the movement causes severe stress points in the concrete.
In hot weather, concrete may crack if joints are not cut within 6 – 8 hours after finishing. The rule of thumb is to cut joints as soon as the concrete is hard enough that the edges don't ravel (dislodging the aggregates) by the saw blade.
Joints should be sawed as soon as the concrete can withstand the energy of sawing without raveling or dislodging aggregate particles. For most concrete work, cutting should take place within the first 6 to 18 hours and never beyond 24 hours.
Control joints are the lines that are cut or tooled into the concrete when the concrete is placed to aid in controlling this tendency to crack by creating weakened planes within the slab.
Alone or as part of another graphic element, lines create patterns, set a mood, provide visual texture, create movement, and define shapes.
Control joints will help prevent cracks caused by thermal expansion and contraction. We recommend using them.
All concrete will shrink slightly as it dries and, when it's set, will expand or contract depending on the ambient temperature. To prevent cracks from forming, concrete expansion joints should be incorporated to allow for movement, particularly in slabs with a surface area exceeding 6m2.
Concrete expands and contracts with changes in temperature and moisture. If not properly controlled, cracks can begin to appear. Placement of concrete control joints and expansion joints are crucial when designing and pouring concrete slabs and sidewalks.
Generally speaking, expansion joints should be no farther apart than 2 to 3 times (in feet) the total width of the concrete (in inches). So for a 4‑inch thick concrete slab, expansion joints should be no more than 8 to 12 feet apart.
There are several benefits of wet cutting concrete, including: Health and safety: Because a constant stream of water turns airborne dust into a slurry, it reduces the risk of respiratory dust exposure. The water cools down the tool more effectively, so there is also a smaller risk of overheating-related hazards.
With any concrete, there is always a chance that you will have cracking because of the potential base material shifting, expansion and contraction due to weather, and other aspects. Making relief cuts ensures that you will have the best chance at limiting large cracks.
Depth of Cut
Simply put, this means that the cutting depth should be restricted to around 2.5 inches for an 8 inch thick concrete slab. In case the cut is too deep, the interlocking may not be sufficient enough for transfer of loads. On the other hand, if it's too shallow, it might result in random cracking.
Driveway. Ideally, the concrete slab for a driveway should be about 100 mm thick, and there is no need for a gravel base.
Never fill your cracked expansion joints with concrete. This removes their flexible nature and can cause your entire floor to crack. Instead, apply an industrial concrete floor caulking or filler designed to resist cracking, allow for concrete expansion and resist water penetration below your floor.
Expansion material is placed between sections of concrete. It's that black stuff you see between concrete slabs sometimes if a contractor doesn't put a sealant on top of it.
Timing is critical for saw-cut joints; cutting too soon spoils the concrete while cutting too late fails to fulfill the purpose. Typically concrete joints should be cut in less than a day, but the specific timing depends on numerous factors, including local conditions, weather and concrete mix.
These lines are called contraction lines and this is going to help in relieving the stress that is going to cause the cracks that are going to be present in the concrete. You may notice these are going to vary in depth, but the concrete line depth is fairly universal in how deep they are going to be cut.
This strength is crucial for things like buildings, roads and driveways. Rebar is not necessary for every concrete project. The general rule of thumb is that if you are pouring concrete that is more than 5 inches in depth, you are probably going to want to add in some rebar to help reinforce the entire structure.