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Angular depressions in the mat mirror the outline of the main screed plate and its rear-mounted, hydraulic extensions. What caused the marks? The haul truck bumped hard into the push compactors on the paver, shoving the screed back and down. Even though the mat had cooled to less than 200¢ª F before the mishap, compaction did not completely remove the marks.

One of the paving crew members stepped off the back of the screed walkway onto the hot mat, resulting in footprints in the mat, visible prior to rolling. Even though the depth of these marks diminished after each pass, the breakdown compactor was unable to completely remove the marks. It is likely that a profilometer running over any of these slight depressions will indicate their presence. There is no reason to walk on an uncompacted pavement, and it should be avoided.

Surface texture differences are visible in the mat. Some of the surface is open-textured, suggesting particle segregation while some of the surface is closed-textured. This also suggests particle segregation. Causes of these surface texture differences were:

• Screed strike-off plate position
• Mix overload from auger length
• One broken auger flight
• Position of the material feed sensor
• Mix cooling during long haul time

Longitudinal surface marks show that the main screed and extensions are not properly adjusted for height. The screed operator adjusted depth controls and was able to remove these streaks within two lengths of the machine. He could also have raised the head of material in front of the main screed and lowered the head of material in front of the extensions to accomplish the same effect. Automation has a chance to work only if proper adjustments are made.

The marks in this base course actually have two causes. The lower mark is a drag mark caused by cool material sticking to the screed. The higher mark is a surface depression from insufficient mix under the screed. Low head of material in front of the main screed led to localized lack of material in the right portion of the auger chamber.