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Pavement transverse cracking is a recurring problem in Canada and the northern United States. Field trials and laboratory investigations have confirmed that the major influence on this cracking is the mix stiffness, and consequently asphalt stiffness, at low temperatures. It has been demonstrated that asphalt stiffnesses predicted from van der Poel's nomograph for both waxy and nonwaxy asphalts correlate with low-temperature pavement cracking trends and consequently can be used to develop low-temperature asphalt specifications. A second approach, based on cracking temperatures predicted from a nomograph using asphalt penetrations at 5 and 25°C, is described as the preferred route for low-temperature asphalt specifications. The soundness of this approach is demonstrated in a specific case where the low-temperature properties of a waxy asphalt are improved by air blowing an otherwise highly crack-susceptible vacuum-flashed residue.
bitumens, pavements, crackin, temperature, asphalts, stiffness, nomographs, specifications, performance evaluation
Senior research chemist, Oakville Research Centre, Shell Canada Ltd., Oakville, Ont.