What role do control joints play in concrete flatwork?

Control joints are an essential feature in concrete flatwork as they serve to allow for movement within the concrete, which is crucial in preventing cracking. As concrete cures and hardens, it undergoes changes in temperature and moisture content that can cause it to expand and contract. Without control joints, these movements can create internal stresses that lead to uncontrolled cracks in the surface.

By providing a designated line of weakness, control joints guide potential cracks to a specific area, which ensures that any cracking occurs along these joints rather than randomly across the surface. This helps maintain the structural integrity and aesthetic appearance of the concrete flatwork.

While the other options may touch on various aspects related to concrete, they do not accurately reflect the primary function of control joints in mitigating crack formation and accommodating structural movement.