Shipping equipment
Concrete without cracks is nearly impossible to find much less achieve. The very nature of concrete is to crack somewhere, it is a mixture of concrete, aggregate, and water.
Cracks are generally caused by the rapid evaporation of the water. Most cracks are aesthetic at best and present no load failure. Unless you are looking at a large crack, then you should contact a knowledgeable and experienced person involved in foundations. They would be able to give you a better explanation.
Do I need to have a soils report?
How thick should I pour my slab foundation?