What happens if you don't saw cut concrete?
In hot weather, concrete might crack if joints are not cut within 6-12 hours after finishing concrete.
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.
Cutting concrete undermines structural integrity: Any time you cut into a slab, you decrease the foundational integrity of the building — no matter how close to a perfect cut you make. You may be able to patch the hole you create well enough to eliminate any aesthetic objections.
The time window for cutting poured concrete can vary based upon weather conditions and mix designs. Cutting freshly poured concrete too late can lead to unwanted cracks in the concrete, rendering the joints ineffective.
Concrete is much thicker and stronger than many other materials in construction, and, therefore, it requires a special process when you need to cut into it. If you want to make any improvements or repairs to your property, and concrete is in the way, you will need to cut the concrete to get it done.
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.
While experience will help you get a better idea of what works for your concrete and climate, there is a rule of thumb to start with. Cuts should be approx. 2-3 times the thickness of your slab in feet.
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.
If you have a concrete floor in your commercial building, you know expansion joints are necessary to allow for the natural expansion and contraction that occurs from temperature changes. Without these joints, large cracks can travel across your floor, creating costly damage.
This type of concrete sawing is also commonly called “flat” or “road” sawing.
Is it better to cut concrete wet or dry?
Contractors mainly use wet cutting for tile work, reinforced concrete, metal, bricks and masonry. It can produce long, clean cuts because it is less prone to overheating or wearing the blade. If electrocution is a potential hazard, consider dry cutting instead.
Once the joint is cut into place, the joint itself is ready to do its job. The joint can then be left as is, sealed, or filled. Sealing or filling should be put off as long as possible to allow the joint to widen, although in practice joints are usually sealed or filled sooner than ideal.
Most concrete and masonry products contain large amounts of sand. When you inhale the dust, silica particles scar your lungs, causing a disabling, irreversible, and incurable lung disease called silicosis.
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.
Never overwork or over finish the surface of any exposed concrete slab. This brings too much fine material to the surface, works out the designed air entrainment*, and will weaken the surface of the slab leaving the top of slab more vulnerable to freeze/thaw damage and sheet scaling*.
Cutting is a technique where the operator moves a material (workpiece) such as metal and the tool in relation to each other in order to shape the workpiece into the desired form through shaving, drilling, etc.
When a recipe specifies how to cut an ingredient, it is important to follow the instructions because using the proper cutting technique will affect the dishes cooking time and will help ensure the food cooks more evenly and maximizes flavour.
The cutting method is based on similar principles to those in the hole-drilling method. Once more, stress is relaxed by the removal of material. This time a notch is removed from a specimen, resulting in the creation of a free edge.
Cracking occurs when shrinkage forces become greater than the strength of the concrete. This can be seen as a race against time between two phenomena: the evaporation of water and the increase in the strength of concrete. This is also true for concrete parts that cannot deform.
Diamond-tipped blades are the best choice for clean, deep concrete cuts. They can be used with a wet or dry saw. A wet saw works best on driveways, sidewalks, and other large flat surfaces, but these industrial-style saws are very expensive.
How do you accurately cut concrete?
Use a standard circular saw, equipped with a corundum or diamond blade, for small tasks. For slabs, it's best to cut through the top inch, then use a sledgehammer to break off the rest. The jagged edge left below the cutting line provides a good rough edge for the new concrete to bond to.
Because the sawed crack control joints offer a point of ingress for water and incompressibles into the pavement structure and base, it's perceived by most road agencies that they should be sealed to keep water and debris out of the structure.
When cutting concrete, small and sometimes large particles of concrete can fly through the air. With a steady jet of water being sprayed on the blade, the water will ensure that any concrete that breaks off while cutting goes straight to the ground away from you and the people you work with.
Usually, 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.
You can install concrete expansion joints before or after the concrete is laid.
Just remember that expansion joints should always be sealed and filled with a flexible joint sealer and never epoxied or coated over. Contraction joints can be filled in the same manner after a coating or sealer is applied if you desire.
The best time to start cutting control joints into concrete is after the poured concrete has dried enough for you to saw through without dislodging or ravelling the particles of the poured mixture. In most cases, control joints should be cut into concrete after it has had 6 to 18 hours of drying time.
Concrete continues to gain strength after pouring for as long as it retains moisture, but the longer it moist-cures, the slower the rate of strength gain. Moist-curing concrete for 20 days more than doubles its strength compared to four days of moist-curing, which is considered a minimum.
Even after exposure to silica dust ceases, the particles remain in the lungs and continue causing damage. This condition is called silicosis, and there is no cure. Chronic silicosis typically occurs after 15-20 years of occupational exposure to respirable silica.
Among granite workers in the U.S. the rate of death from silicosis doubled at a cumulative exposure of less than 1 mg/m3. A recent study of pottery workers found high rates of silicosis, up to 20%, among workers with an average exposure of 0.2 mg/m3 over many years.
How cancerous is concrete dust?
Unfortunately, inhaling concrete dust can cause serious and even fatal diseases such as silicosis, COPD (chronic obstructive pulmonary disease), and lung cancer because it usually contains silica.
Angle grinders and circular saws use round diamond blades to cut through concrete. The deepest you can get with a standard blade is around 4 inches. But a Sawzall can cut through slabs much thicker because the blade is 9 to 12 inches. The best Sawzall blade for cutting concrete is one with carbide teeth or grit.
When concrete is not cured properly, its durability, strength and abrasive resistance are affected. Due to inadequate curing, concrete develops plastic shrinkage cracks, thermal cracks, along with a considerable loss in the strength of the surface layer.
Problems with concrete include construction errors, disintegration, scaling, cracking, efflorescence, erosion, spalling, and popouts.
Concrete starts hardening as soon as it's poured, but it's far from ready. Give it at least 24 hours of concrete cure time before allowing any light foot traffic and even longer before putting any significant weight on the surface.
Masonry blocks, bricks, and concrete slabs contain concentrated amounts of crystalline silica. When these materials are dry-cut they release silica containing dust into the workers' breathing zone. Regular exposure to this hazardous dust can lead to the development of silicosis, a deadly and incurable lung disease.
As with most construction tasks, cutting concrete is inherently hazardous. But ensuring that you have the right training for the equipment you're using, performing a hazard assessment before each task, and ensuring you're wearing the correct PPE will go a long way toward minimizing the danger and potential for injury.
Silica is a substance naturally found in certain types of stone, rock, sand and clay. Working with these materials can create a very fine dust that can be easily inhaled. Once inside the lungs, it causes swelling (inflammation) and gradually leads to areas of hardened and scarred lung tissue (fibrosis).
Harmful Effects of Concrete Dust
Respiratory System – when inhaled through the mouth and nose, concrete dust can cause an allergic reaction, irritation of the mouth, nose, throat, and lungs. Prolonged exposure can lead to lung cancer and other respiratory diseases like silicosis.
Fine particles created by cutting and grinding can get deep into the lungs. Most concrete and masonry products contain large amounts of sand. When you inhale the dust, silica particles scar your lungs, causing a disabling, irreversible, and incurable lung disease called silicosis.
What are the dangers of concrete?
Cement and cement-based products can harm the skin in a number of ways. Wet cement is highly alkaline in nature. A serious burn or ulcer can rapidly develop if it is trapped against the skin. In extreme cases, these burns may need a skin graft or cause a limb to be amputated.
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.
Cement can cause ill health by skin contact, eye contact, or inhalation. Risk of injury depends on duration and level of exposure and individual sensitivity. Hazardous materials in wet concrete and mortar include: alkaline compounds such as lime (calcium oxide) that are corrosive to human tissue.