What do control joints primarily relieve in concrete?

Control joints are specifically designed to manage and relieve stress in concrete that arises from changes in temperature and moisture levels, leading to expansion and contraction. As concrete cures and hardens, it undergoes dimensional changes; variations in temperature, humidity, and water content can cause the material to expand or contract significantly.

Without control joints, these stresses can result in cracking, as the concrete is unable to accommodate the shifts in size. By incorporating control joints, the concrete can move more freely, and any cracking will typically occur at the joints rather than through the body of the slab. This proactive approach helps maintain the structural integrity and aesthetic appearance of the concrete surface over time.

The other options pertain to different concerns that do not align with the primary purpose of control joints. For instance, pressure build-up from embedded reinforcement relates to the structural design and placement of rebar rather than thermal stresses. Water accumulation during curing is more related to curing techniques and moisture management than to the need for joints. Lastly, weight loads from furniture and equipment are considerations in the overall design and thickness of concrete slabs but are not directly alleviated through the use of control joints.