In general, cracks in the floor are not a cause for concern. The only time you might worry is if the cracks start to change vertically, suggesting that some settlement is taking place. Tight cracks are common in concrete slabs. In general, if the crack is stable and does not leak water, it does not indicate a structural problem.
In most cases, these are shrinkage cracks that formed when the concrete cured. I am often asked about cracks in concrete foundations. Many homeowners get nervous when they see cracks in the concrete and wonder if they are bad or dangerous. While it's a natural reaction to worry when you see something cracked, the reality is that 95% of cracks in concrete are harmless and there's nothing to worry about.
When new concrete hardens, shrinkage always occurs. And because concrete is not an elastic material, cracks are unavoidable and are rarely a cause for concern. When you hear that a concrete mix has a strength of 2000, 3000, 4000, or more than 5000 PSI, it refers to the pounds per square inch that would be needed to crush that concrete slab. When non-crystalline silicon dioxide (mainly originating in Portland cement) reacts with alkali hydroxide in concrete or alkalis present in the environment, such as sea spray or groundwater, the reaction forms an alkali silicate gel that swells as it absorbs moisture from the cement pore surrounding solution in concrete or environment.
ALL concrete cracks and you need to understand this problem and realize that most concrete cracks are safe. During the initial setting of concrete, plastic settling cracks form while the concrete remains plastic. Certain cracks in the concrete can best be repaired by targeted injection of the appropriate material adapted to the diagnosis of the individual crack, followed by a suitable concrete protective coating. In addition to appearance, cracking cracks do not greatly affect the strength or durability of concrete as long as water intrusion does not occur, which can lead to subsequent deterioration of the concrete.
The pressure causes the concrete to form cracks near the steel that, over time, will lead to more extensive cracking as rust builds up until the concrete begins to peel off the reinforcing steel bars (chipping off the concrete) and exposes the corroded reinforcing steel rods. I have posted your photos of both the concrete step settlement and the cracks in the stamped concrete yard along with your question here for other readers to comment. Pouring concrete when conditions are too high (above 77°F) (if any) means that some of the water that hydrates the concrete evaporates rather than bonding in the chemical reaction, increasing the chances of shrinkage cracking and creating a weak slab. Since concrete cannot shrink around a corner, stress will cause the concrete to crack from the point of that corner.
If the concrete cover protecting the reinforcing steel is damaged and the joint between the concrete and the steel reinforcing bar breaks, the passive layer of the steel will break and active corrosion of the steel will begin. Old and new concrete do not intermix and as a result, a so-called “cold joint” forms, creating a weakness in the concrete and a possible passage for water ingress. For a narrow crack like this, you can use a self-leveling concrete crack filler to seal the crack before painting or finishing the surface. An expansion joint is used in the concrete to allow the concrete to absorb the intended motion as it expands or contracts with daily temperature variations.
The alkali-aggregate reaction refers to a destructive expansion reaction within concrete that occurs over a long period of time (more than 5 years) in the concrete. .
