Non-structural cracks may not affect the integrity and strength of a concrete structure, but they can still be a problem if left untreated. This is because they can provide a passage for materials to penetrate the concrete. When concrete is still in its plastic state, it is full of water. As the slab loses moisture during curing, it shrinks.
This shrinkage can cause the slab to crack in order to relieve stress. Shrinkage cracks are common and can appear as soon as a few hours after the slab has been poured and finished. Crazing cracks after hardening may be the result of excessive buoyancy that tends to draw water and cement to the surface, resulting in weak concrete subject to high shrinkage stresses. More often, they are the result of poor curing.
Other cracks that occur after hardening may be due to lack of adequate reinforcement at corners, insufficient depth of concrete over reinforcement bends, nesting of reinforcing steel in the concrete, or lack of expansion and contraction joints. When it comes to cracks in concrete foundations, many owners worry if they are bad or dangerous. While it is natural to worry when you see something cracked, the reality is that 95 percent of cracks in concrete are harmless and nothing to worry about. Plastic shrinkage cracks are probably the most common reason for first cracks in concrete.
This is because when concrete is poured, it contains a lot of water which takes up space and makes the slab a certain size. As concrete is a very rigid material, this shrinkage creates stress in the concrete slab. As the concrete shrinks, it is dragged along its granular sub-base which impedes its free movement and can pull the slab apart. Excess water in the concrete mix can also increase the likelihood of cracks.
When placing concrete, avoid adding additional water to the mix as this will evaporate from the concrete, causing further shrinkage. Be sure to choose the right concrete mix for your project. Concrete provides structures with strength, stiffness and resistance to deformation but these characteristics mean that concrete structures lack flexibility to move in response to environmental or volume changes. Cracking is often the first sign of concrete deterioration but it is possible for deterioration to occur before cracks appear.
Cracking can occur in both hardened and fresh, or plastic, concrete as a result of volume changes and repeated loading. The repair method should be selected based on an assessment of the crack and the objective(s) of the repair. If rust stained, run lengthwise or more than hairline cracks are present or worsening, it would be wise to consult a structural engineer. After fixing all concrete cracks, consider adding an epoxy coating to the garage floor. Cold joints are intentionally placed in the concrete by contractors when pouring the concrete and wire mesh usually comes in rolls or sheets and is placed in the centre of the slab; in a 4-inch thick slab it would be about 5 inches from the top and 5 inches from the bottom of the slab. The control joints create a weak spot so that when the concrete shrinks, it cracks at this joint rather than randomly throughout the slab. It is important not to ignore cracks in concrete as they can be an indication of more serious problems such as settlement of loose soil due to flooding, seepage or poor management of roof and surface runoff which can send water under a building. Understanding why cracks occur and their significance will help you apply appropriate repair methods such as using a flexible concrete-coloured sealant to keep water out of joints between steps and other surfaces.
