pavement is a well-graded (dense or open) sandy gravelor clean sand.Maximum size of the aggregate, ingeneral, is limited to two thirds of the compactedthickness of the layer. Loose thickness is approximately1 1/4 times the desired compacted thickness.“Surface moisture” is defined as the film of wateraround each particle of stone or sand. The amountpresent is determined by heating a weighed sample ofaggregate at 212°F in an open pan and stirring it with arod until the surface water disappears (3 to 10 minutes).The difference between the original and final weights isconsidered to be moisture lost during drying. The lossin weight, expressed as a percent of the final or dryweight, is the moisture content, allowed before theaggregate is mixed with asphalt cutbacks or road tars.When the aggregate is too wet, it should be worked withmechanical mixers, graders, or improvised plows toallow the excess moisture to evaporate. For cutbacksand tars, moisture content of coarse-graded aggregateshould not exceed 3 percent, and of fine-gradedaggregate, 2 percent. For emulsions, moisture contentof coarse-graded aggregate should not exceed 5 percent,and of fine-graded aggregate, 3 percent.The quality of the road-mix pavement dependslargely upon the control of the mix. The percentageof bitumen will vary in relation to the absorptivequality of the aggregate, rate of evaporation of thevolatile substances, and other factors. Although anexact formula is difficult to follow, proportioningmust be controlled within narrow limits to assure thestability and life of the mix.With dense-gradedaggregates especially, too much bitumen should notbe used. All particles of the completed mix should becoated and uniform in color. When the mix is too lean,the aggregate in the windrow will stand almostvertically and have a dull look; and when the mix istoo rich, it will ooze or slip out of shape. When themix is correctly proportioned, a handful, squeezedinto a ball, will retain its shape when the hand isopened.Road-mix pavements should be constructed onlyon a dry base when the weather is not rainy.Atmospheric temperature should be above 50°F.Mixing should take place at the temperature of theaggregate, but not below 50°F or above therecommended temperature of the liquid asphalt beingused. The construction procedure depends uponwhether the base is a newly constructed base, ascarified existing base, or an existing pavement.When a newly constructed base is used, perform thefollowing procedure:1. Inspect and condition the base.2. Prime the base and allow the prime to cure.3. Haul in and windrow the aggregate at the side ofthe primed base. (Allow the aggregate to dry or aeratewith a blade when wet.)4. Spread the aggregate on the cured prime baseone half of the roadbed width.5. Spray the bitumen on the aggregate in incre-ments of about one third of the total amount required.6. Mix the bitumen with the aggregate; blade backand forth until a uniform mix is obtained.7.mixed.8.9.10.Repeat as directed in (5) and (6) until thoroughlySpread the mix to the specified thickness.Compact the surface.Apply a seal coat when necessary.For a scarified base, the aggregate is scarified whenit is not available from other sources. The constructionprocedures are as follows:1. Loosen the aggregate from the base.2. Dry and breakup all lumps of material.3. Blade into parallel windrows of uniform size atone side or in the center.4. Sweep the base, when needed5. Prime the base and allow time to cure.6. Continue as directed in (4) through (10) inthe above procedures for a newly constructed base.When an existing pavement is to be used as a base,the construction procedures are as follows:1. Sweep the base.2. Apply a tack coat and allow it to cure.3. Bring in the aggregate and deposit in windrowsat the side of the cured, tacked base.4. Aerate the aggregate.5. Spread the aggregate on one half of the tackedbase.6. Spray bitumen on the aggregate in increments ofabout one third of the total amount required7. Mix the bitumen with the aggregate by blade.8. Spread the mix to specified uncompactedthickness.16-13nl I
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