If you're about to pour concrete for your sidewalk, you're going to want to know why cracks appear in newly poured concrete. After all, isn't it designed to withstand a variety of pressures, including heat from the sun and the pressure of shrinkage when drying? Absolutely, but there are several mistakes that can be made when pouring your sidewalks, including:
- Too much water in the mix – excessive water will cause your slabs to shrink more than they can structurally handle: in some extreme cases, as much as a half-inch per 100 feet
- Excessive heat causing the concrete to dry too quickly – when concrete dries too quickly, it reacts negatively to the pressure: the interior concrete should still be drying for a few days after the surface has solidified
- Too few control joints – these items must be installed every 8–12 inches in your concrete in order to create controlled expansion cracks that allow your concrete to expand and contrast: too few of them will cause the concrete to crack
Solving These Problems
To avoid falling a victim to these problems and to have a high-quality sidewalk, you need to solve each concern one-by-one. The first problem is easily solved. If you're pouring your sidewalk yourself, you should try to have a water to concrete ratio of 0.6 to 0.7. This means for every pound of concrete, you should have 9.6–11.2 ounces of water.
Similarly, it shouldn't be too difficult to install expansion joints every 8-12 inches in your concrete. However, the second problem is trickier to solve. Your sidewalk will crack if it reaches temperatures over 158 degrees Fahrenheit.
You can help cool it by mixing it with ice water and using Class F fly ash or slag cement to replace a small portion of the dry cement, but no more than 10 percent. It's also not a bad idea to install shade over top of the sidewalk to keep it from absorbing too much sunlight.
Evaluating The Cracks If They Do Occur
While your sidewalks shouldn't crack if you follow the above steps, cracks may still occur. Crack evaluation requires inspecting the location of the cracks and using crack measuring equipment to gauge where they originated. These include the use of a comparator, a device that measure the depth and length of the crack, including the potential range of movement.
After identifying where the cracks are originating, you need to seal them with concrete sealant. The small nature of most sidewalk cracks (due to the small size of individual slabs) means you shouldn't have a hard time identifying the location of the cracks nor should you have to use a large amount of sealant to repair the cracks.
For more information, talk to a professional like Certified Material Testing Products.Share