Control joints, or contraction joints, are sometimes confused with expansion joints, but have a different purpose and function. Concrete and asphalt have relatively weak tensile strength, and typically form random cracks as they age, shrink, and are exposed to environmental stresses (including stresses of thermal expansion and contraction). Control joints attempt to attenuate cracking by designating lines for stress relief. They are cut into pavement at regular intervals. Cracks tend to form along the cuts, rather than in random fashion elsewhere. This is primarily an aesthetic issue; the appearance of even, regular cracking, which may be hidden in the joint’s crevice, is often preferred over random cracking.