Most cracks in concrete occur within 2-3 days of being laid. In about a month, these fine cracks should disappear. Shrinkage cracks can appear on the surface within hours of pouring concrete, but it takes a full month for the concrete to fully settle. These very fine cracks are often referred to as cracks and usually occur because the surface dried too quickly or the tile did not cure properly.
While they may not be pretty, there is nothing to worry about as this is usually just cosmetic and the slab is still structurally sound. There are products that can be used to solve this problem, such as Quikrete slab rejuvenation video. The Concrete Supply Company (CSC), as we know it today, was formed in 1958 through the merger of three premixed companies. When you see a crack in the concrete slab or wall, the first assumption is that something has been done wrong, but that's not always the case.
In reality, cracks in concrete are very common and some are even unavoidable. Below we explain 6 of the most common types of cracks in concrete. When the concrete is still in the plastic state (before hardening), it is filled with water. When the water finally comes out of the slab, it leaves large voids between the solid particles.
These voids make concrete weaker and more prone to cracking. This type of cracking is known as “plastic shrinkage cracking” and usually occurs 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 it to crack from that point. Plastic shrinkage cracks 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. 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.
Like a balloon, heat causes concrete to expand and when it pushes against anything that stands in its way (a brick wall or an adjacent slab, for example), it may be enough to cause cracking if neither has the ability to flex. Expansion joints are used as a separation point (or insulation) among other static surfaces and should act as shock absorbers to relieve stress and prevent cracking. The freeze-thaw cycle can also cause cracking in concrete. When the ground freezes, it can sometimes rise many centimeters before thawing and settling down again.
This ground movement caused by freeze-thaw is a huge factor contributing to concrete cracking. If the tile cannot move freely with the ground, it will crack. The roots of large trees can have a similar effect on a slab if they are too close; growing roots can lift and crack the concrete surface. Soil settlement below a concrete slab can also cause cracking when a vacuum is created in the ground below the surface due to large tree removal or utility company digging trenches for lines, pipes etc., without compacting soil when they fill it up again.
Excessive weight on top of a concrete slab can also cause cracking despite its strength; when you hear that a concrete mix has a strength of 2000, 3000, 4000 or more than 5000 PSI, it refers to how much pressure would be needed to crush that concrete slab. In residential settings, real slab overload is not as common; instead what is more likely to occur is excessive overloading on the ground below the slab after heavy rain or snow melt when it's soft and damp. Residential homeowners who place large RVs or trash bins in their driveways are more likely to see these types of cracks. Two common types of cracks caused by premature drying are crack cracks and crusting cracking.
Crack cracks are very fine, shallow cracks that look like cobwebs or broken glass which occur when top of a concrete slab loses moisture too quickly. Crusting cracking generally occurs during concrete stamping process when sunny or windy days cause top of slab to dry faster than bottom; when seal is embedded it separates surface near stamped joints causing small cracks around outer edges of “stones” which are not structural problems but unsightly nonetheless. It is often difficult to determine exactly what caused a particular crack but proper site preparation, quality mixing and good concrete finishing practices can go a long way in minimizing occurrence of cracks and producing aesthetically pleasing project.
