Expansion joints are an integral part of concrete structures. They are built into deck systems to control the stresses of volume changes in concrete. Depending on the type of construction (cast-in-place, precast, etc.), joints are installed to isolate ramps, buildings, and large expanses of deck surface. They may also be needed to provide free rotation of deflecting members. Most joints open and close according to daily and seasonal fluctuations in deck surface temperatures. Joints provide a natural place for water, salts, and debris to collect. They also present a hazard to pedestrians who may trip over them. To prevent these problems, joint seals can be installed. Seals must be designed for the intended movement of the joint, as well as for water tightness, wheel action (traffic, equipment), pedestrian safety, and reparability.