Before concrete hardens when it is in its plastic state, it is full of water. Upon curing it looses moisture and the shrinking creates stress which can pull the slab apart. When the stress becomes too much for the hardened concrete, the slab will crack to relieve pressure. This is especially common in warmer weather. If too much water was used in the mix, once the excess water evaporates, the slab is left with large voids which make the concrete weaker and prone to cracking. This is commonly known as shrinkage cracking. To combat shrinkage cracking control joints are added into the slab. Control joints are grooves that are tooled into new concrete or sawed into concrete after it reaches its initial set. Control joints create a weak place in the slab so when the concrete shrinks, it will crack on the joint instead of in the slab.
Expansion joints on the other hand occur in warm weather when the concrete expands after a freeze-thaw cycle. This causes stresses since the concrete will expand and push towards any object in its path. If there is nothing flexible between the slabs the concrete will be forced to crack to relieve tension. By filling the expansion joints with a flexible material, it will act as a shock to relieve the stress and prevent future cracking. Heaving, settling and overloading are other common types of concrete cracks. Heaving cracks occur after a freeze-thaw cycle when the frozen ground lifts and settles when the ground thaws. If the slab is not free to move with the soil, the slab will crack. Settling cracks occur if there is a void in the ground and the ground continues to settle. Overloading cracks occur when there is excessive weight on top of a slab that is too much for the ground to handle. Spider cracks, and crusting cracks will cause aesthetic damage but do not pose any actual threat to the concrete. Instead they are visually unappealing but do not cause a structural problem.
In order to prevent concrete from cracking there are a few methods of remediation:
1.) Reinforced concrete: although reinforced concrete can also crack and can cause concrete to crack by restraining shrinkage, if cracks do occur the reinforcement can help hold the slab together.
2.) Prime with Lithi-Tek 4500 to densifiy and fortify concrete and protect from premature cracking. Wait seven (7) days and then apply the Siloxa-Tek 8500 as a topcoat sealer. The Siloxa-Tek 8500 will help to mitigate moisture, protect from freeze-thaw cycles and deicing salt degradation that can harmfully erode rebar and result in cracking.