A new kind of ultrathin surfacing, intermediate between chip seal and very thin asphalt hot mix, has appeared recently. it basicallyconsists of a layer of hot precoated aggregate, spread over a binder spray application. a specifically designed machine spreads both binder and coated aggregate in a single pass and smooths the course. the machine includes a receiving hopper, conveyors, binder storage tanks, a variable-width spray bar, and a light heating screed unit with extensions. it operates at high speed, currently about 20 m/min. the binder is a modified emulsified asphalt. its application rate varies between 0.6 and 1.2 kg/sq m. the friction course itself consistsof an aggregate, mostly 6 to 10 mm in size, coated with a mortar made of sand, filler, and asphalt cement. the latest content ranges from 5 to 5.5 percent. the course thickness is between 1 and 2 cm. itsapplication rate of total mix is between 23 and 28 kg/sq m. the resulting surfacing is homogeneous. it offers a rough macrotexture and high levels of skid resistance. it has shown some capacity of leveling existing small irregularities of the support. its rolling noise is significantly lower than that of chip seals made with aggregate ofthe same size. to date, the behavior of this friction course appears to be promising, as no deterioration of any kind has been observedafter 2 years, even under heavy traffic. this paper appears in transportation research record no. 1304, highway maintenance operations and research 1991.
Abstract