Why? Concrete less than 5″ thick is more prone to cracking, unfortunately this includes almost every poured slab out there. 4″ thick slabs are twice as resistant to fractures (heavy loads from above and lifting from below) as 3″ slabs. This occurs when the weight of an object on a slab stresses concrete beyond its tensile strength. This cracking often occurs, for example, when a heavy truck passes over a sidewalk designed only for pedestrian and light vehicle traffic.
To avoid stress load cracking, make sure the slab is built on a well-drained, evenly compacted subgrade and that it is thick enough to withstand the type of use it will receive. In residential concrete, 4 inches is the minimum thickness for hallways and patios. Garage slabs and driveways should be 5 to 6 inches thick if heavy truck traffic is expected, otherwise 4 inches is sufficient. While plastic shrinkage cracks can occur anywhere on a slab or wall, they most often occur in reentrant corners (corners that point toward the slab) or with circular objects in the middle of a slab (pipes, plumbing fixtures, drains, and manholes).
Since concrete cannot contract around a corner, stress will cause the concrete to crack from the point of that corner. Shrinkage cracks in plastic are usually very narrow in width and barely visible. Although they are almost invisible, it is important to remember that plastic shrinkage cracks not only exist on the surface, but extend throughout the thickness of the slab. Excessively wet mix is a contributing factor to shrinkage in concrete.
While water is an essential ingredient in every concrete mix, there is such a thing as too much water. When the mixture contains too much water, the tile will shrink more than if the correct amount of water were used. Hot weather is another big reason for plastic shrinkage cracks. In general, cracks wider than a credit card and running through the depth of concrete are structural in nature and could be a sign of more serious problems (see Evaluating Concrete Crack Repair).
Even the American Concrete Institute has no standards or recommendations that give an affirmative or negative answer as to which cracks need repair based on width and other factors. Identifying the types of cracks in concrete can help you determine the cause and take steps to prevent further cracks in the future. During the setting and hardening steps, excess mixing water in the concrete evaporates, causing the concrete to dry from the surface inward. If your concrete is a little older, a concrete repair professional can help you fix the cracks.
The American Concrete Institute addresses the issue of concrete cracking in its American Concrete Institute manual, ACI 302.So, of course, it's frustrating to spot fine cracks, especially if you've just paid for a new driveway, concrete slab, walkway, or garage floor. When properly installed, concrete is one of the most durable and long-lasting products you can use in your home. When you hear that a concrete mix has a strength of 2000, 3000, 4000, or more than 5000 PSI, it refers to the pounds per square inch that would be needed to crush that concrete slab. Proper site preparation, quality mixing and good concrete finishing practices can go a long way in minimizing the occurrence of cracks and producing a more aesthetically pleasing concrete project.
One of the most common mistakes made by DIYers who are new to concrete is adding too much water to the dry concrete mix to make mixing easier, leading to weak concrete and a high risk of cracking. On sunny or windy days, where the top of the slab dries faster than the bottom, the top of the concrete surface may become crusted. Quikrete, a company with nearly 80 years of experience, offers a range of solutions for all types of cracks, including its new line of advanced polymeric sealants, which includes self-leveling sealant for use in cracks in horizontal concrete surfaces and anti-sag sealant for fixing cracks in vertical concrete surfaces without sagging or sagging. Consult an engineer or concrete repair professional to determine the cause of the crack and recommend the best repair solution.
This is done by cutting grooves one-third the thickness of the slabs, and is done as soon as the concrete is hard enough to withstand damage from the saw. Understand what your contractor is doing with respect to each of the items listed above and you will get a good concrete job. . .
