Cracks are often caused by normal shrinkage of concrete as it hardens and dries. Cracks in concrete can range from being unsightly and non-structural, to being detrimental to the structural integrity and safety of a building. I am often asked about cracks in concrete foundations. Many homeowners get nervous when they see cracks in concrete and wonder if they are bad or dangerous.
While it is a natural reaction to worry when you see something cracking, the reality is that 95% of cracks in concrete are harmless and there is nothing to worry about. Cracks in concrete are extremely common, but they are often misunderstood. When a homeowner sees a crack in his slab or wall, especially if the concrete is relatively new, he automatically assumes something is wrong. It's not always like that.
Some types of cracks are inevitable. The best thing a contractor can do is try to control cracking. This is done by properly preparing the subbase, making sure that the concrete is not too wet, using reinforcement where necessary, and correctly placing and spacing the crack control joints and expansion joints. However, cracks sometimes occur despite the precautions taken.
I have posted your photos of both the concrete step settlement and the cracks in the stamped concrete patio along with your question here for other readers to comment. Pouring concrete when conditions are too high (above 77 degrees F) (your case) means that some of the water that hydrates the concrete evaporates rather than coalesces in the chemical reaction, which increases the chances of shrinkage cracks and makes the slab weak. If a structural contractor drives a piece of heavy equipment loaded with wood on a 4-inch thick concrete slab, it can crack green (not fully cured) concrete. We place rebar in several strategic places to prevent concrete from settling and moving away from the places where it should be.
If a crack line is more or less straight, and if it extends into the foundation walls or more or less at right angles to the foundation wall, then if the foundation wall and the base had settled, you would expect to see cracks in the same area. After you have repaired all the cracks in the concrete, consider adding an epoxy layer to the garage floor. Some other causes of long-term driveway cracks include everything from nearby trees to heavy vehicles. They accomplish this by passing thick steel cables through the concrete, then squeezing them and securing them to the outside of the concrete.
An unreinforced concrete slab will crack substantially more than a reinforced slab and is weaker. The idea behind filling the cracks is to seal them to prevent moisture and air from entering the concrete. While plastic shrinkage cracks can occur anywhere on a slab or wall, they almost always occur at reentrant corners (corners that point toward the slab) or with circular objects in the middle of a slab (pipes, plumbing fixtures, drains, and sewers). If you see a pattern of cracks or rust on the garage floor that looks like the cracks are 12 to 24 inches apart in one or two directions, it may be an indication that the rebar was placed a little too high and does not have enough concrete to properly cover the rebar.