Seal Coat Design for Unbound Granular Pavements Carrying Heavy Axle Loads
Authors
Bryan D. Pidwerbesky
University of Canterbury, Christchurch, New Zealand
Greg Arnold
Logging Industry Research Organisation, Rotorua, New Zealand
Abstract
Virtually all of the public highway pavements in New Zealand are comprised of usually one or more coats of a sprayed seal over unbound granular layers. The standard New Zealand design and construction techniques are being applied to heavy-duty forest roads. Seal coats are an attractive economic alternative for low-volume roads but existing design procedures are inappropriate for the loadings that are experienced on the arterial forest roads.
The advantages and limitations of seal coat design with respect to forest roads are discussed in this paper. Experimental work which has been instigated to further the development of seal coat design, construction techniques, and specialized materials suited to the special requirements of forest roads sustaining heavy loads of up to 160 kN per single axle is described and discussed. Results of field trials thus far have shown that enhanced quality control during construction, reduced bitumen application rates, and use of polymer-modified bitumens are providing the required performance.
