The minimum recommended compacted thickness is three times the nominal maximum size aggregate. When the mat falls below this thickness, it pulls, tears, cools rapidly and generally will not be able to achieve the proper density and pavement smoothness. Back To Contents Back To Top Automatic Screed Controls Manually controlled screeds must be adjusted by the screed operator as paving progresses to maintain grade control. Automatic screed controls, however, are designed to adjust automatically to place a uniform mat of desired thickness, grade and shape. Automatic control systems have several advantages over manually controlled screed systems.
Automatic controls help disassociate the screed from erratic vertical movement of the tractor unit.
Automatic controls adjust the screed tow points to enable the screed to follow a parallel path to the grade and slope of the reference system, which may be different from the path plane of the tractor unit. Automatic controls normally need to operate for a distance of five to seven times the pull arm length to achieve a balanced system. The system reaches equilibrium when the resultant forces of the screed are parallel to the grade reference. A single grade control system is one that grade control is set for one side of the paver. The opposite side is controlled from the grade side by using the cross slope device.