Precast Adjustment Unit
Definition - What does Precast Adjustment Unit mean?
Precast adjustment units are used in manholes for the purpose of adjusting elevation for installing grates and covers. They are made of precast concrete or prefabricated rubber and are either circular or rectangular in shape.
The adjustment units can be used instead of bricks, are easy to install and can be done quickly even by semi-skilled labor. They have a lesser number of joints, making it especially useful for preventing inflow/infiltration of water.
Trenchlesspedia explains Precast Adjustment Unit
Precast adjustment units are 65 mm deep reinforced units that can be used in place of traditional bricks to set the manhole covers or grates to the required road elevation.
Concrete adjustment units can be used along with rubber adjustment units but the rubber units should be placed for the final surface and should never be placed under concrete units.
Precast concrete adjustment units are set in a full mortar bed and rubber adjustment units are bonded to the adjacent surface using a continuous strip of butyl tape on the top surface brick course or the concrete adjustment unit. These units can be used for a maximum raise of 1 meter including previous extensions.