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In northern climates, paving becomes a problem in colder months when ambient temperatures do not meet the specifications set by governing agencies. A typical specification is that paving can only be done when ambient temperatures are a minimum of 10ºC (50ºF) and rising, or base mat temperatures are 2-3ºC (35-37ºF) and rising. Either contractors lose money waiting for the sun to shine enough to meet these specifications, or agencies relent and allow paving because "it has to be done". This will lead to future pavement problems as the cold base asphalt steals the heat from the new hot mix before the new lift can be compacted, preventing the formation of a good bone. If a tac coat is applied in very cold weather it will not work to provide the bond, and, in fact, it may provide a mechanism for de-bonding, and so it is often skipped.
Lack of compaction in asphalt pavement has been shown to affect life cycles by 30-40%. See infrared camera documentation of bade pavement temperatures after heating to ensure good base asphalt temperatures.
Paving in cold weather can cause ravelling, slippage, increased moisture retention, increased cracking, and delimitation and slippage with the base.
HDE infrared heaters have been used on major highways in Ontario since 1996, extending the paving season and ensuring a better quality construction. In Oklahoma a customer attaches a 16'x6' HDE infrared heating deck directly to the paver, behind the matter transfer vehicle, heating the base asphalt to 90ºF at paving speeds. This allows paving for full days in winter months when they may otherwise have to sit for two to three hours waiting for good ambient temperatures.
In 1997 HDE heaters were used by a major paving contractor in Ontario to pave over a milled surface on the 401 and 402 (main transportation routes through the province), allowing 60,000 tons of hot mix asphalt to be placed in late November and early December when they were faced with allowing the milled surface to be left until the spring, causing significant safety problems. The new course bonded well, with no problems, and lasted many years. In northern Ontario when a bridge fail occurred on the Trans Canada highway in mid-January it was necessary to build a detour in the coldest month of the year.Concerns of delimitation of the final surface were alleviated when HDE infrared heaters were used to pre-heat the base asphalt in temperatures of -8ºC (17-18ºF). The detour lasted until spring break-up when the bridge was put back in service. No problems were encountered when the surface course on the detour, even with the high traffic of transports driving.
The infrared heater decks can also be purchased to dry concrete bridge decks in the late fall weather and to allow the safe application of waterproofing membranes and subsequent pavement structure.