In Western Australia sprayed seals, laid on thin unbound granular bases, typically have lives of 16 years before a reseal is needed.This type of cheap pavement, using naturally occurring materials, should be ideal for the long lengths of low-volume roads found in theUnited States. A case history of a seal laid as part of an asphalt cement durability experiment is presented. Extensive data on construction and performance are thus available for this seal, which is typical of hundreds of kilometers of road on either side of the experiment that are giving the same performance and that were laid to the same construction standards and with essentially the same materials. A sand primer seal was first placed on a base consisting of 160 mm unbound, naturally occurring gravel laid over a compacted natural clay sand subgrade. The primer seal was trafficked for 6 months and then the final seal applied. This consisted of Class 160 (85/100 pen) asphalt sprayed at rates varying from 1.3 to 1.6 L/m2 and covered with 14-mm one size aggregate, spread one stone thick at a rate of 88 m2/m2. The site is in an area of low rainfall but high summer temperatures. Traffic at the site is low (100 to 200 veh/day - total both directions) but with regular heavily loaded road trains. Pavement deflections were measured using a Benkelman beam and typically were of the order of 0.3 mm. The sections have been inspected every year andare in excellent condition 13 years after construction, with the exception of one section laid with a low-durability asphalt. This performance is typical of seal coats in Western Australia that are commonly used as surfacings on roads carrying in excess of 1, 000 veh/day and not infrequently on roads carrying as much as 15, 000 veh/day (total both directions). The factors contributing to long seal life arethe use of durable asphalts, the seal design procedure, and the construction practices used.
Abstract