light rolling and brooming. Excess prime, held in minordepressions, should be corrected by an application ofclean, dry sand.Any loose sand should be lightlybroomed from the primed surface before the wearingsurface is laid.The primed base should be adequately cured beforethe wearing surface is laid. In general, a minimum of48 hours should be allowed for complete curing.Ordinarily, proper surface condition is indicated by aslight change in the shiny black appearance to a slightlybrown color.When a soil base is to be covered by a bituminouswearing surface, the area should be barricaded toprevent traffic from carrying dust or mud onto thesurface both before and after priming. If it is necessaryto open the primed base course to traffic before it hascompletely cured, a fine sand may be used; when youare ready to place the wearing surface, lightly broom thesand from the primed base course.To estimate the amount of bitumen required for theprime coat, multiply the area to be treated by the rate ofapplication (ROA).NOTE: Under certain conditions, the estimateshould include sufficient bitumen for an additionalwidth of 1 foot on each side of the surface course to beconstructed on the primed base.The formula for a prime coat estimate is asfollows:10% at .10. This will depend on theexperience of the asphalt distributortruck crew.Example: the specification and other data for aprime coat application are as follows:For computing gallons:Step 1:L =W =9=WF =length of treated section in feetwidth of treated surface in feetsquare feet per yard conversion factorWaste factor of bitumen = 5% at .05 orAlways round your answer to the next highernumber. In this case, 7761.6 is rounded to 7762 gallons.Tack CoatA tack coat is an application of asphalt to an existingpaved surface to provide bond between the existingsurface and the asphalt material to be placed on it. Twoessential requirements of a tack coat areas follows: (1)it must be thin and (2) it must uniformly cover the entiresurface to be treated. A thin tack coat does no harm tothe pavement, and it will properly bond the course.Some of the bituminous materials, used for tackcoats, are rapid-curing cutbacks, road tar cutbacks,rapid-setting emulsions (may be used in warm weather),and medium-asphalt cements. Because rapid-curing16-7
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