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Pervious friction courses gain in popularity The use of 4en- graded asphalt pavements for the prevention of hydroplaning, the wet - weather phenomenon i which a vehicle's tires lose contact with the road due to a thin film of water on the pavement's su face, is gaining ac- ceptance among highway au- thorities in Europe as well as the United States, according to a re- cent report by the Asphalt Insti- tute. Highway experts feel that the wet-weathE r accident rate can be reduced if rainwater is quickly removed from roadway surfaces via pervious wearing courses. Motorway atithorities in Den- mark have placed experimental pervious asphalt friction courses on I two sections of pavement of that country's arnum Motorway, reports the Institute. Five more sections will e used on the soon-to-be-corripleted Elsinore Moto Tway. no reflective cracks have ap- peared, and the rubber emulsion kept water out of the pavement's base course. We have been satisfied, thus far, with its scuff resistance, and all -in -all, it's a very/ durable pavement. 7 The project AAas supported by the U.S. Federal Aviation ;Ad- ministration and the Okla oma Aeronautical C mmissiom FAA cooperated in developing the specifications for the )surfacing and encouragec I us td use the open - graded mixes because of its demonstrated in pr ved skid re- sistance and ab lit to eliminate hydroplaning. The skid fact( /r of the resur- faced portion � our 6200 -ft run- way is 62 to 65, as measured by the Oklahoma S ate Highway De- partment. ■■ The Danish pervious course uses 83% crushed rock (maximum -'/8-inch), 15% crushed rock fines, 2% hydrated lime filler, and a binding agent of 4.1% to 4.3% 100- penetration grade asphal The pervious mix also includ s 0,4% of an amine -type antist Ip- ping agent. The Danish experiments f Ilow the precedents set in Engla d and the U.S. England has use open - graded friction cours since 1yb7, and pervious friction Courses are becoming more common in the U.S. when skid prevention is necessary. More information on the de- sign and construction of open - graded asphalt pavement is avail- able from the Asphalt Institute, College Park, Md. Ask for Open - Graded Asphalt Friction Courses, publication No. 10 in the Institute's Construction Leaflet series. ■■ Wearing course deAgn mix vs. job mix, Bartlesville municipal airport Sieve - Design Limits Size (i passing) Job Mix (i passing) 3/& -inch ! 100 100 No. 4 25 -65 33 No. 8 15 -25 20.6 No. 16 3 -15 13.6 No. 200 3-5 4.1' % Asphalt 5.0 -8.0 7.0'" 'Includes 1.5° hydrated lime •60 -70 pen ration asphalt with 2.0 ppm DC -200 silicone agent > resurfacing the old pavement, a three -ft plastic strip was placed over all cracks joints to prevent reflection cracking. MARCH 1975 / THE AMERICAN CITY • 65 t