Cracks in concrete are inevitable. Whether it is from long-term wear and tear or shrinkage upon drying, concrete will crack.
This complex phenomenon is dependent on several factors — and many are
oftentimes out of the builder’s hands. For concrete to remain smooth and
undamaged, it must dry unrestrained. This is virtually impossible
because restraints are necessary to support the weight of the structure.
Most of these cracks do not affect the stability and durability of the structure. However, it is imperative that you know how to identify different types of cracks and ascertain the superficiality of the damage. This will help you avert any major structural issues in the future.
Recognising Cracks in Concrete and How to Deal with Them
Plastic Shrinkage
- Plastic shrinkage in concrete is identifiable by the fine and shallow cracks on the hardened surface.
- These cracks are caused by the evaporation of water as the mixture dries. They are more pronounced when there is excessive water as this leaves large voids in the hardened concrete.
- Cracks caused by plastic shrinkage are cosmetic in nature and will not impact the structure’s durability.
To avoid plastic shrinkage, make sure to use half a pound of water for every pound of concrete.
Premature Drying
There are two types of cracks that are prevalent with premature drying: crazing and crusting.
- Crazing cracks are fine and spider web-like in nature.
- Crusting cracks are small and occur around the edges of stamped concrete.
- Both types are considered surface cracks and do not affect the structure’s integrity.
These cracks are hard to prevent as they are dependent on the environmental conditions of the site. However, they are easily fixed with the proper concrete repair products.
Expansion and Contraction
- Expansion and contraction cracks are represented by straight and long cracks on the surface of the concrete.
- Hardened concrete will expand and contract when exposed to drastically changing temperatures.
- These cracks are superficial and will not affect the structural integrity of the concrete slab.
To limit the number of cracks caused by contraction and expansion, place control joints to separate the slabs and to give them room to move.
Overload
- Pressure cracks or breakage are clear indicators of overloading.
- Although
a durable building material, concrete has weight limits. When too much
weight is placed on the slab, it alters the ground underneath which
causes it to break.
- Unlike most cracks, the breakage that happens with overloading can lead to structural problems that will need to be addressed as soon as possible.
To avoid this type of damage, determine the pound-force per square inch (PSI) that the concrete slabs can handle without cracking.
Heaving and Settling
- The cracks that occur with heaving and settling are large and spread out like a spider web.
- Ground movement is unavoidable. This results from several natural factors which include:
- The freeze-thaw cycle of soil;
- Large, overgrown tree roots; and
- The settlement of soil due to the decomposition of surrounding plant life.
- The cracks that result from these scenarios can lead to structural problems that undermine the stability of the surface.
To avoid this type of damage, thoroughly prepare the site prior to laying out the concrete and apply the necessary solutions such as the use of void forms.
While cracks in concrete cannot be completely avoided, preventive measures can be taken to control the spread and the seriousness of the damage. Proper site preparation and the application of best practices will effectively produce concrete structures that are sound and aesthetically pleasing.