How To Determine Mix Cooling Time
MultiCool is a user-friendly, simple computer program that calculates the rate of cooling in an HMA mat during construction. It requires that the user input such items as the time of day (entered automatically according to the computer's clock), latitude, air temperature, wind speed, mix information and lift thickness for each HMA lift, type of material being paved over, its temperature and whether or not the soil or base are frozen. The program then computes how quickly each lift of HMA will cool and when the next lift may be placed. This allows field personnel to make decisions concerning cold weather paving and the scheduling of HMA deliveries to the paving site. While it is no substitute for good judgement and on-the-job observations, it can help in the planning process and in field decision making.
The graph below was generated using MultiCool, and it shows that on a 40 degrees Fahrenheit day, the wind speed and the thickness of the paved lift have profound effects on the amount of time available for compaction. On a windy day 20 mph), paving a thin lift (1.5 inches), only about 12 minutes is available before the mix cools to 175 degrees Farenheit, whereas paving a 3-inch lift on a calm day will allow for more than 40 minutes to get density in the mat.
MultiCool was developed by Professor Vaughan Voller and Dr. David Timm at the University of Minnesota for the University of California. Dr. David Timm is currently at the Department of Civil Engineering and National Center for Asphalt Technology at Auburn University. It is actually the second generation of a computer program called PaveCool developed for the Minnesota Department of Transportation. PaveCool was limited to one lift of paving as opposed to multiple lifts.
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For questions about MultiCool, please e-mail the engineering department.