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How Temperature Impacts Compaction
Paving crews can improve their finished pavement by keeping the rollers close to the paver and to each other
The proper position of the roller train behind the paver aids compaction efforts. The paver needs to place the mix while the temperature is between 350˚F and 290˚F. To the right of the paver are two "breakdown rollers" working in tandem in a temperature range between 320˚F to 250˚F. The arrow indicates where "density tests" are best conducted (after the breakdown rollers) and the furthest right section shows where finish rolling is done (temperature range 150˚F to 100˚F.)
By Dale Starry
Two things must happen in order for a paving train to achieve a uniform final density of any mix. First, the mix must be delivered to the project in a homogeneous and non-segregated condition. Second, the compactors in the paving train must be close enough to the paver to work on the pavement while the mix is still hot and viscosity is low.
The industry has adopted many processes in an attempt to assure mix uniformity. The most common culprits in aggregate and temperature segregation are poor practice at the mix plant and improper truck loading, hauling, or mix delivery. While asphalt should always be properly loaded and hauled to the jobsite, mix segregation can be overcome through the use of a material transfer vehicle (MTV).
Assume that an HMA mix is delivered to the paver in excellent quality and that the paver is in excellent working order. The crew has properly made all screed adjustments and automatic controls are being utilized to achieve the required grade and slope of the pavement surface. Everything has progressed according to plan and the material placed on grade is ready for compaction to produce finished pavement.
If this mix is a Marshall mix, it is ideally delivered to the paver at a temperature between 260˚ and 280˚F . If this mix is a Superpave mix, it should be delivered to the paver at a temperature between 300˚ and 330˚F.
Naturally, environmental factors affect the rate of mix cooling during and following placement. Studies indicate that the majority (about two-thirds) of heat loss following laydown is into the base. Mix should be delivered to the paving site at a temperature of at least 250˚F for a Marshall mix or 290˚F for a Superpave mix immediately behind the paver screed.
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