applied with a bituminous distributor in three equalapplications.Each application is one-third of theamount required.Immediately following each application of thebituminous material, the treated aggregate should bemixed with spring-tooth or double-disk harrows,graders, rotary tillers, or a combination of thisequipment until all the particles of the aggregate areevenly coated. When a grader is used, the windrow ismoved from side-to-side by successive cuts with theblade.Several graders can operate, one behind the other,to reduce the total time required for complete mixing.In hilly terrain, blading should be from the bottom to thetop, as the mix tends to migrate down. After all theaggregate has been mixed, the mix should be bladed intoa single windrow at or near the center of the road andturned not less than four complete turns from one sideof the road to the other. Excess bitumen, a deficiencyof bitumen, or uneven mix should be corrected by theaddition of aggregate or bituminous material, followedby remixing.Mixing should continue until it iscomplete and satisfactory; remember, mix will set up ifmixed too long.Suppose that materials, weather conditions, andequipment are well-suited to mixed-in-place paving, butthe road or airfield must carry traffic duringconstruction.In such cases, the windrowing ofaggregate and the mixing and spreading of bitumen maybe done elsewhere–on any area of smooth groundwhich can be compacted for the purpose or on anyunused road or airfield surface. The road or airfieldsurface, base, or subgrade to be paved is then primed ortack-coated as required to complete construction and tokeep portions of the road or airfield open to traffic. Assoon as the prime or tack coat cures, the mix is pickedup, trucked to the jobsite, dumped, and then bladed intowindrows for spreading.The bituminous mix should not be spread when thesurface is damp or when the mix itself contains an excessof moisture. The mixed material should be spread to therequired width in thin, equal layers by a grader orfinisher. (When a finisher is used, additional supportequipment is required, and the material must be split intotwo windrows for an 8- to 12-foot-wide pavement.)When spreading the mix from a windrow, you shouldtake care to prevent cutting into the underlying subgradeor base course. To prevent such cutting, you shouldleave a layer of mix, approximately one-half inch thick,at the bottom of the windrow.16-16The material being spread should be rolled onceand then leveled with a grader to remove irregularities.The remaining material should be spread and rolled inthin layers until the entire mix is evenly spread to thedepth and width specified. During the spreading andcompacting, the surface should be dragged or bladed, asnecessary, to fill any ruts and to remove corrugations,waves, or other irregularities. Both pneumatic-tired andsteel-wheeled rollers may be used for rolling all surfacetreatment jobs; however, the pneumatic-tired roller isthe preferred type.After all layers have been satisfactorily spread, thesurface should be rolled with two-axle tandem rollers.Rolling should begin at the outside edge of the surfaceand proceed to the center, overlapping on successivetrips at least one half of the width of the wheel of theroller. Alternate trips of the roller should be of differentlengths. The speed of the roller at all times should becontrolled to avoid displacement of the mix. Lightblading (or floating) of the surface with the graderduring rolling may be required. Rolling should becontinued until all roller marks are eliminated andmaximum density is obtained. To prevent adhesion ofthe mix to the roller, you should keep the roller wheelmoist with water; use only enough water to avoidpicking up the material. At places not accessible to theroller, the mix should be thoroughly compacted withhand tampers. When the surface course becomes rough,corrugated, uneven in texture, water soaked, or trafficmarked, unsatisfactory portions should be tom up andreworked, relaid, or replaced. When forms are not usedand while the surface is being compacted and finished,the outside edges should be trimmed neatly in line.When the road-mix pavement surface course isconstructed from an open-graded aggregate, a surfstreatment may be required to waterproof the surface. Asurface treatment is unnecessary on a dense-graded,well-compacted, road-mix pavement.When possible, traffic should be kept off freshlysprayed asphalt or mixed materials.When it isnecessary to route traffic over the new work speed mustbe restricted to 25 mph or less until rolling is completedand the asphalt mixture is firm enough to withstandhigh-speed traffic.DEFECTS IN FLEXIBLE PAVEMENTSDefects inflexible pavements can be placed into oneof five classes. These classes are cracking, distortion,disintegration, slippery surfaces, and surface treatmentproblems.
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