The time available for compacting the layer depends mainly on the following conditions during placement:
• The mixture temperature behind the paver
• The air and surface temperatures and wind velocity
• The layer thickness
The matters of temperature are elaborated on in Section 10.3.2.
In extremely adverse weather conditions, the time for compacting is counted in minutes and is often less than 5 minutes. After that time, the mixture temperature falls to a level at which the high viscosity of binder makes the movements of the mixture particles impossible. If the SMA layer has to be placed in difficult conditions, the following organizational issues should be remembered:
• Using the best possible insulation during SMA mixture delivery
• Closely coordinating the mixture deliveries in relation to the spreading speed with no stoppages and shutdowns of the paver or trucks delivering mixture to a work site
• Discharging consecutive mixture deliveries to the paver hopper before it is completely emptied
• Effectively heating of the paver screed
• Maintaining the proper paver speed to avoid the following:
• Decreased effectiveness of the paver compaction
• The risk of dragging chipping particles out by the screed
• Keeping the rollers close behind the paver and having more of them than when compacting in good conditions
• Calculating the limited time of effective rolling caused by the drop of mixture temperature in the layer; being aware of weather conditions, the temperature of a delivered mixture, and the layer thickness, one can roughly estimate the time required for compacting using ready-made curves, measuring the layer cooling rate, or calculating it with the use of computer software such as PaveCool or MultiCool.
