Cracks and gaps in concrete are more than just an eyesore. Water can get into the joints, freeze and then expand, making the cracks even larger. Gaps against a house can direct water against the foundation, leading to more problems. Once a year, go around your home and look for these gaps and joints to prevent problems. Concrete cracks of any type are the bane of many homeowners. They can be in flat slabs, retaining walls, foundation walls and steps. Concrete has fantastic compressive strength, but usually only 10 percent of that in tension when you try to pull or stretch it apart. This lack of tensile strength explains, for the most part, why concrete cracks.