Which type of joint is designed to create lines of weakness in concrete?

Control joints are specifically designed to create lines of weakness in concrete, allowing for controlled cracking. When concrete is poured and subsequently dries, it undergoes shrinkage, which can lead to random cracking if there are no planned weaknesses in place. Control joints facilitate this cracking at predetermined locations, ensuring that the cracks are less noticeable and occur where they are intended, thereby preventing unsightly damage to the finished surface.

Isolation joints exist to separate the concrete from adjacent structures, helping to accommodate movement without damaging the surface. Construction joints, on the other hand, are used where there is a stop in the pouring process and may not serve the purpose of creating weakness in a planned manner. Expansion joints allow for movement due to thermal expansion, but they do not create controlled weaknesses like control joints do. Each of these other joints serves a distinct purpose, but none specifically creates the intentional lines of weakness that control joints are designed for in concrete.