hydraulic system for the truck-bed hoist should befrequently inspected to guard against hydraulic fluidleakage. Such leakage on the roadway surface willprevent good bonding between the roadway and the newmat. When enough oil is spilled that the mix can absorbit, the mix can become unstable at that spot. For thisreason, leaking trucks should not be used.Tarpaulins should be pulled over the mixture duringhauling in cool weather or on long hauls to protect themixture from excessive cooling. A cool mix forms lumpsand a crust over its surface. When a tarpaulin is used, caremust be taken to be sure it is securely fastened to the topof the truck bed so that cold air cannot funnel under it.During delivery, the driver must direct the trucksquarely against the paver and should stop the truck a fewinches from the paver before the truck tires make contactwith the paver roller bar. Backing the truck against thepaver can force the screed back into the mat, leaving abump in the pavement even after the mat is rolled.The truck bed must be raised slowly. When the mixis dumped too rapidly, segregations occur, because thecoarser aggregates will roll down the sides of the load.BOTTOM-DUMP TRUCKS.— Bottom-dumptrucks can be used when a grader is spreading the mixor when a pickup device is used to feed the windrow leftby the truck into the paver hopper.Two common methods for unloading bottom-dumptrucks are in use. The first method involves the use ofa spreader box, designed to be operated under the gatesof the truck. The amount of material, placed in thewindrow, is governed by the width of the spreader boxopening. The disadvantage of this method is that thespreader box can restrict the amount of material to lessthan the required amount. The second method, which isused more often than the first, is to use chains to controlthe dump gate opening.NOTE: Automatic devices are also available forcontrolling gate openings.Variations in the size of the windrow, deposited bythe bottom-dump truck for pickup by the paver, andirregularities in the surface on which the material is tobe placed will cause variations in the amount of materialfed to the paver hopper. This often causes variations inthe finished surface. It is, therefore, essential that thewindrow, deposited by the truck be as uniform aspossible.When the windrow is deficient in size,material can be added to it to keep the paver fromstarving. When the windrow contains too much mix, ashort gap in depositing with the next truck willcompensate for the excess. The windrow length mustalso be controlled particularly in cool weather.Windrowed material will cool below spreading andcompaction temperatures in cool weather, particularlywhen delay occurs because of paver malfunction. Thelimit of the windrow should be no more than one truckload ahead of the pickup machine to prevent excessivecooling of the mix in cold weather.When the loader and paver are directly coupled,vibration of the pickup device maybe transmitted into thepaver, causing ripples and roughness in the mat surface.These vibrations generally result from worn and defectiveparts or from improper mounting or adjustment.Truck HitchesThe purpose of a truck hitch on the front of the paverhopper is to keep the truck dumping hot mix into thehopper in contact with the paver. If, during dumping,the truck and the paver separate and hot mix spills, itmust be cleaned up before the paver passes over it.Two types of truck hitches are in common use. Onetype uses an extension that reaches under the truck andhooks onto the rear axle of the truck. The other type ofhitch has retractable rollers that are attached to the truckpush bar and grip the outer side of the rear wheels of thetruck. The rollers revolve with the wheels while thetruck dumps its load into the hopper.Pivoted Truck Push RollersThe pivoted push roller is a device, mounted on thefront of the paver, that adjusts when alignment between thetruck and paver is uneven. This device reduces the unevenforce exerted on the paver by the misaligned truck,minimizing interference in the steering of both vehicles.ASPHALT FINISHERS (PAVERS)Various makes and models of asphalt finishers areused by the Naval Construction Force (NCF). Twotypes are shown in figure 16-38. Even though thefinishers may operate differently, their primary jobs areall the same: receiving asphalt and spreading it in apredetermined, uniform length, width, thickness, andshape. The finisher also provides initial compaction ofthe mat (layer of mixture in place.)Because asphalt finishers are different, you mustalways read the operator’s manual for the unit you areoperating. It is also good to have a practice sandlaydown before actually using a hot mix. This is tofamiliarize yourself and others with the machine andalso ensure that the machine is working properly. Figure16-39 shows a practice laydown, using just theaggregate mix without the asphalt.16-34
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business