SURFACE TREATMENTSA surface treatment is an application of asphaltmaterials to any type of road surface with or without acover of mineral aggregate. This application producesan increase in thickness usually less than 1 inch. Surfacetreatments have a variety of uses. They waterproof,provide a nonskid wearing surface, and rejuvenate anold surface.PurposesThe simplest types of bituminous surfaces that maybe placed over prepared surfaces are called surfacetreatments.Surface treatments are applications ofbituminous material to any type of base or pavementsurfaces which, together with an aggregate cover,produce a pavement with a thickness of 1 inch or less.In some cases, multiple treatments that produce thickerpavements are used.Surface treatments are applied for one or more ofthe following purposes:1.2.3.4.5.6.TypesWaterproof the surface.Provide a wearing surface.Make the surface nonskid.Prevent hydroplaning.Rejuvenate an old road or runway.Make permanent improvements.Surface treatments may be applied to the basecourse of a new road or to the surface of an old road asa method of repair. Surface treatments are grouped intothree categories: sprayed asphalt, sprayed asphalt withcover aggregates, and asphalt-aggregate mixtures.Sprayed Asphalt Surface TreatmentSprayed asphalt treatments contain no aggregates.They are simply applications of different types ofasphaltic materials to a prepared surface. The categoriesinclude fog seals, dust laying, and road oiling. Primeand tack coats are also considered as a sprayed asphalttreatment.FOG SEAL.— A fog seal is a light application ofdiluted slow-setting asphalt emulsion, used to renewold asphalt surfaces and seal small cracks and surfacevoids. Fog seals are especially useful for pavementscarrying a low volume of traffic. A fog seal may also beused for the following:1. To seal surface voids in new asphalt plant mixes2. To prevent dust on sprayed asphalt with coveraggregate surface treatments3. To increase aggregate retention4. To provide a uniform dark colorThe asphalt emulsion is diluted with an equalamount of water, and the diluted material is sprayed atthe ROA of 0.1 to 0.2 gallon per square yard, dependingon the texture and dryness of the old pavement. Innormal conditions, the separation and evaporation of thewater is rapid, permitting traffic within 1 or 2 hours.DUST LAYING.— Dust laying consists ofspraying an untreated surface with a low-viscosity liquidasphalt, such as SC-70, MC-30, MC-70, or a dilutedslow-setting asphalt emulsion. The asphalt and dilutantpenetrate and coat the fine particles and temporarilyrelieve the nuisance of dust.The material is sprayed at a ROA of 0.1 to 0.5 gallonper square yard. When emulsion is used, it should bediluted with 5 or more parts of water by volume.Diluted emulsion dust-laying treatments usually requireseveral applications. The dust stirred by traffic betweenapplications eventually conglomerates and no longerrises. This is an effective treatment in a very dustyenvironment where one application of asphalt isinsufficient.ROAD OILING.— Road oiling differs from dustlaying in that it is usually accomplished as part of aplanned buildup of low-cost road surfaces over severalyears. Each application may be mechanically mixedwith the material being treated, or it maybe allowed topenetrate. The light oils in the road oil penetrate into thesubgrade and tend to repel moisture absorption. Theobjective in all road oiling work is to form a dustlesswearing surface, combined with a strongwater-repelling subgrade.Because soils vary widely, procedures for oiling area matter for local trial and error, rather than scientificanalysis. The amount of road oil, required in the firstyear of work will vary from 0.75 to 1.0 gallon per squareyard. The first application is applied at the ROA ofabout one half of the total; succeeding applications aremade in equal amounts.Road oiling treatments are placed several weeksapart, depending upon the character of the asphalt soilmat. If some breakup occurs after the first winter, light16-23
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