an asphalt-paving project is the temperature at the timeof compaction.During rolling, the roller wheels must be kept moistwith only enough water to avoid picking up material.Rollers move at a slow, but uniform, speed with the drivewheels nearest the paver. The speed should not exceed3 mph for steel-wheeled rollers or 5 mph forpneumatic-tired rollers. A roller must be maintained ingood condition, capable of being reversed withoutbacklash. The line of rolling should not be suddenlychanged or the direction of rolling suddenly reversed,because these actions will displace the mix. Anypronounced change in direction should be made onstable material.When rolling causes material displacement, theaffected areas should be loosened at once with lutes orrakes and restored to their original grade with loosematerial before being rerolled. Heavy equipment,including rollers, should not be permitted to stand on thefinished surface before it has thoroughly cooled or set.Rolling freshly placed asphalt mix is done in thefollowing order:1.2.3.4.5.Transverse jointsLongitudinal jointsBreakdown or initial rollingIntermediate or second rollingFinish rollingThe five steps in rolling freshly placed bituminousor asphalt mix are covered in chapter 11 of thisTRAMAN.MIXED-IN-PLACE CONSTRUCTIONEmulsified asphalt and many cutback asphalts(although the use of cutbacks is declining) are fluidenough to be sprayed onto and mixed into aggregate atmoderate to warm weather temperatures. When this isdone on the area to be paved, it is called mixed-in-placeconstruction.Although mixed-in-place is the moregeneral term and is applicable whether the constructionis on a roadway, parking area, or airfield, the term roadmix is often used when construction is on a roadway.Mixed-in-place construction can be used forsurface, base, or subgrade courses. As a surface orwearing course, it usually is satisfactory for light andmedium traffic, rather than heavy traffic. However,mixed-in-place layers, covered by a high-quality asphaltplant-mix surface course, make a pavement suitable forheavy traffic service. The advantages of mixed-in-placeconstruction include the following:1. Utilization of aggregate already on the roadbedor available from nearby sources and usable withoutextensive processing.2. Elimination of the need for an asphalt mixingplant. Construction can be accomplished with a varietyof machinery often more readily available, such asmotor graders, rotary mixer with revolving tines, ortraveling mixing plants.ROAD-MIX PAVEMENTSRoad-mix pavements consist of mineral aggregateand mineral filler uniformly mixed in place with abituminous material and compacted on a prepared basecourse or subgrade. A single layer, about 1 1/2 inchesto 3 inches thick, is generally used. This type ofpavement is likely to become defective unless it has asound, well-drained subgrade and is well-mixed,uniformly spread, and properly compacted. Road-mixpavements may be used as a wearing surface ontemporary roads and airfields and as a bituminous baseor binder course in construction of more permanenttypes of roads and airfields. Road mix is an economicalmethod of surfacing small areas when aggregate can beused from the existing base or when satisfactoryaggregate is nearby.For road-mix pavements, the grade and type ofbituminous material depend upon the aggregate andequipment available as well as weather conditions andtime required to complete the project. Good weather isimportant to the success of a road-mix project. Wherepossible, road-mixing operations should be scheduledwhen weather conditions are likely to be hot and dryduring, and for some time after, the project.Recommended types of bituminous materials suitablefor road mix are asphalt cutbacks, asphalt emulsions,and road tars. A medium-curing cutback is generallyused in a moderate climate, and a rapid-curing cutbackis used in a cold climate.Viscosity required isdetermined by the temperature, aggregate gradation,and method of mixing. The highest viscosity that willcompletely and uniformly coat the particles of aggregateshould be used. In general, open-graded aggregaterequires a high viscosity; a gradation, containingmineral filler, requires a less viscous grade.Aggregate, used in road mix, may be scarified fromthe existing subgrade or hauled in from a nearby source.A wide range of coarse and fine aggregate and mineralfiller may be used. The ideal aggregate for road-mix16-12
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