Expansion joint
Expansion joint turns up in 2 fields: refractories, waterproofing. Here is what it means to the people in each one.
Expansion joint in refractories
Gap deliberately left in a lining so bricks or castable can grow with heat without crushing or lifting.
A planned space in brickwork or a monolithic lining that takes up thermal expansion, filled with ceramic fiber, or with cardboard and other combustible spacers that burn away. Too little allowance causes pinch spalling, bulged walls and crowns that lift off their skewbacks; too much leaves open joints for slag and metal to run into. Silica and magnesia, which expand more than 1 percent on heating, need the most careful layout.
"Put the cardboard in every fourth expansion joint like the drawing says, mag grows and that ring will pinch without it."
Expansion joint in waterproofing
A designed gap between building elements that lets them move with temperature, settlement and load without cracking.
Expansion joints separate panels, slabs, cladding and structures so thermal growth, shrinkage, wind sway and settlement close and open the gap instead of breaking material. The gap is sealed with an elastomeric sealant, a preformed seal or a manufactured cover system. Joint width is calculated from the expected movement and the sealant's movement capability, not chosen by habit.
"Expansion joint at the parapet's 3/4 inch, but the design movement says we need a full inch even with a class 50."