What is the purpose of control joints in concrete slabs?

The purpose of control joints in concrete slabs is to minimize cracking by providing predetermined weak points in the concrete. As concrete cures and hardens, it undergoes shrinkage due to moisture loss and temperature changes. This shrinkage can lead to uncontrolled cracking if there are no measures in place to direct where the cracks will occur. Control joints are specifically designed to create a planned fracture line, which helps to alleviate stress by allowing the concrete to crack in a specified location rather than in random patterns, thereby protecting the integrity of the slab and maintaining its aesthetics.

The other options focus on aspects that are not the primary function of control joints. Enhancing surface finish and increasing tensile strength are not relevant to control joints, as those features pertain more to mix design and finishing techniques. Similarly, while curing rates can influence the overall properties of concrete, control joints do not facilitate or impact the curing process directly.