The upper temperature limit that permits compaction is around 149 °C (300 °F). The upper temperature limit is affected by the characteristics of a mix at high temperature. If the mix is above 149 °C (300 °F), a bulge might occur on each side of the wheel. The mat will constantly shift, and the mat will not compact. Increasing the distance between the paver and the compactor will solve temperature problems. The increase in distance will allow the mat to cool. When the mix cools to around 85 °C (185 °F) little gain or no gain in density is possible. One solution to cold mixes involves increasing the force of compaction. A second solution is the use of multiple compactors on the job. A third solution is compacting close to the paver.
The test strip should be a straight run that is at least 150 m (500 ft) long. The test strip should be part of the actual job. The following items are revealed from the test strip: measure of the target density, quality of the ride, proper compactive force, proper amplitude, proper rolling speed, proper rolling pattern and the rate of production for the equipment.
One trial and error method for creating a test strip is reducing the rolling speed of the compactor and performing a nuclear density test after every completed pass of the compactor until the target density of the test strip is reached. The next step is increasing the rolling speed while the same number of passes is used. Test the density again. Continue this method until density fails to pass. The result will be the highest rolling speed and the number of passes that will achieve the target density. The results will show the highest production rate that the compactor can operate while the mat still meets the requirements of density and surface finish.
An increase in air temperature decreases the cooling rate of asphalt mixtures. The increase in air temperature allows more time for compactors to achieve desired density in the mix. Higher air temperatures improve the flow of the mixture during compaction. In some cases, high air temperature can make a mix unstable and difficult to compact.
Wind can also affect compaction. The mix will cool quickly with a strong wind. Velocity of the wind is more of a problem in cold weather.
Rain during the production of asphalt can also affect compaction. Rain in the aggregate type of mix can reduce the overall temperature of the mix that is being compacted. Water in the mix can also make the mat unstable during compaction.
A good rolling pattern provides the uniform thickness and efficiency needed to meet density. A good rolling pattern will meet the requirements for smoothness. A good rolling pattern will allow the compactor to match the production of pavers. The pattern should be determined on the test strip. The pattern will establish the number of passes that are needed to cover the mat. Also, the pattern will establish the number of passes that need to be repeated in order to achieve density.
 | |
| Illustration 1 | g00804485 |
The figure shows a typical rolling pattern. The compactor begins the pattern on material that has been previously compacted. The compactor begins at the right edge or the left edge of mat (1). The operator turns on the vibratory system when rolling speed has been reached, if equipped. The compactor should be operated in a straight line at a constant speed. The machine should stop at a predetermined distance from paver (2). The application and the type of mix affects the distance between the machines. The distance between the machines is usually 6 m (20 ft). The operator completes the first cycle by repeating the first pass in reverse. When the machine approaches the starting point, the operator should gradually turn the machine to a new starting point (3). The new starting point should provide a 152.4 mm (6 inch) overlap from the uncompacted mat to the compacted mat. The third pass has an identical form to the first pass. The third pass will be longer than the first pass. The pass will be longer because the paver has moved forward by this time. The sequence continues until the full width of the lane is compacted. The reverse pass of the first set of passes is the starting point for the next set of passes.
If marks occur, the reversal should be completed differently. Marks in the mat occur most often because of a thick mat, a soft mix, or round aggregate in the mix.
In order to prevent a mark, the operator should slightly turn the machine as the machine comes to a stop. Turning the machine will allow the line of the reverse pass to be easily rolled.
The rolling method that is chosen is affected by the design parameters of the project.
The procedure for compacting a longitudinal joint involves rolling along the joint with all the wheel surface on the hot side. The wheels force the hot asphalt into the joint. During the second pass, overlap the cold mat about 152.4 mm (6 inch).
 | |
| Illustration 2 | g00736768 |
Compacting unconfined edges is done differently than a longitudinal joint. Make the first pass about 152.4 mm (6 inch) away from the edge. The first pass adds strength to the mat. During the second pass, the asphalt that was compacted supports the weight of the tires. The edge is compacted but the edge is not pushed out.
Edges that are confined require a similar rolling pattern to the method for the longitudinal joint. Make the first pass along the joint. On thick lifts, some of the material that is hot can be forced onto the cold side. This material cannot be adequately compacted and much manual work must be done in order to clean up the process. An alternate procedure involves rolling the first pass with most of the tires on the cold side and a 152.4 mm (6 inch) overlap on the hot side. The position of the tires will close the joint before compacting the hot side.
 | |
| Illustration 3 | g00804490 |
Compactors are constantly changing direction during asphalt compaction. Improper reversing can cause mat defects. There are different ways to reverse the compactor so that marks are not left on the asphalt. Turn across the hot mat when you prepare to stop and reverse. Any created marks will be in the direction of the tires. The created marks will be easier to roll away on successive passes. Some mats are very stiff and the mats can tolerate a straight stop without deforming. In order to determine the proper technique for reversing, you should use various techniques. When possible, you should stay on the hot side of mat (4). If you roll off the mat, the compactor will probably cause a bump when you pass over the joint onto the cold side. Stay on the hot mat and turn to the area that will be compacted on the next pass (5). Finally, you should avoid stopping on the hot mat. You should roll off the hot mat onto the cold side or shoulder (6). You should find a level spot on the joint when you roll off a mat in order to prevent a bump in the mat.
 | |
| Illustration 4 | g00804491 |
When you compact a road with a crown or a superelevation, you should compact upward from the outside edge toward the center crown. The pattern creates strength in the mat at the outside in order to support the compactor as the compactor moves toward the center of the road. Overlap the crown by no more than 152.4 mm (6 inch) in order to avoid distorting the crown (7) .
Note: Never straddle the crown in an attempt to save a pass.
Transverse joints should be compacted in a manner that is transverse rather than in the direction of paving. Position the compactor mostly on the cold side of the joint. Overlap the hot side by 152.4 mm (6 inch) in order to pinch the joint together. You might need to build a ramp on each side of the road in order to get the compactor into position. Finish rolling should be done in the direction of paving in order to eliminate any marks.