6.5.3 Spreading by Asphalt Paver
Pavers used for spreading of asphalt operate on a ‘floating screed’ principle (Figure 6.2). During paving, the screed is supported by the asphalt being spread. This also provides partial compaction of the asphalt. The thickness of the asphalt layer is determined by the height of the towing arm and angle of attack of the screed. Changes to thickness are achieved by changing the height of the tow point and/or changing the angle of the screed relative to the tow arm. Changing the angle of attack of the screed produces a gradual change in asphalt thickness until a new equilibrium state is achieved.
Adjustments to the tow point and screed angle (Figure 6.3) may be made manually, or controlled automatically by sensors referenced to an adjoining paved surface, levelling (or averaging) beam attached to the paver, fixed reference line or by computer-programmed level data.
Minor changes to the finished level will also be introduced by changes in the head of the material in front of the screed, changes in paver forward speed, and changes in asphalt stiffness due to changes in mix temperature. Smooth, continuous operation is therefore an important factor in achieving high standards of ride quality. The rate of delivery of the asphalt should be arranged so that the paver can operate at a uniform speed. Paving should not commence until sufficient asphalt is on site to ensure continuous operation.