Years ago, many bridges had unsealed joints. A simple gap in the deck accommodated small movements, and finger-plate joints or similar systems accommodated larger movements. Water and debris simply fell through the joints. Transportation departments, however, have paid a price for this joint simplicity. Water and deicing salts drip onto substructure elements, causing major rebar corrosion. Even if corrosion is not an issue, many states require leakproof joints for environmental reasons. Thus many open joints must be fitted with a neoprene trough and drainage system to catch water and debris that falls through them.

To overcome these problems, many states are replacing their remaining open joints with sealed ones. Although there are many different types of sealed expansion joints, the most common systems are field-poured sealants, compression seals, strips seals, sheet seals, plank seals and modular joints. The suitability of each type for a particular application depends on the amount of movement expected at the joint.