SURFACE TREATMENTS A surface treatment is an application of asphalt materials to any type of road surface with or without a cover  of  mineral  aggregate.  This  application  produces an increase in thickness usually less than 1 inch. Surface treatments have a variety of uses. They waterproof, provide  a  nonskid  wearing  surface,  and  rejuvenate  an old  surface. Purposes The simplest types of bituminous surfaces that may be placed over prepared surfaces are called surface treatments. Surface  treatments  are  applications  of bituminous  material  to  any  type  of  base  or  pavement surfaces  which,  together  with  an  aggregate  cover, produce a pavement with a thickness of 1 inch or less. In some cases, multiple treatments that produce thicker pavements are used. Surface  treatments  are  applied  for  one  or  more  of the  following  purposes: 1. 2. 3. 4. 5. 6. Types Waterproof  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 base course of a new road or to the surface of an old road as a method of repair. Surface treatments are grouped into three  categories:  sprayed  asphalt,  sprayed  asphalt  with cover  aggregates,  and  asphalt-aggregate  mixtures. Sprayed Asphalt Surface Treatment Sprayed  asphalt  treatments  contain  no  aggregates. They  are  simply  applications  of  different  types  of asphaltic materials to a prepared surface. The categories include fog seals, dust laying, and road oiling. Prime and  tack  coats  are  also  considered  as  a  sprayed  asphalt treatment. FOG SEAL.— A fog seal is a light application of diluted slow-setting asphalt emulsion, used to renew old asphalt surfaces and seal small cracks and surface voids. Fog seals are especially useful for pavements carrying a low volume of traffic. A fog seal may also be used  for  the  following: 1. To seal surface voids in new asphalt plant mixes 2.  To  prevent  dust  on  sprayed  asphalt  with  cover aggregate  surface  treatments 3. To increase aggregate retention 4.  To  provide  a  uniform  dark  color The  asphalt  emulsion  is  diluted  with  an  equal amount of water, and the diluted material is sprayed at the ROA of 0.1 to 0.2 gallon per square yard, depending on the texture and dryness of the old pavement. In normal conditions, the separation and evaporation of the water is rapid, permitting traffic within 1 or 2 hours. DUST   LAYING.—   Dust  laying  consists  of spraying an untreated surface with a low-viscosity liquid asphalt, such as SC-70, MC-30, MC-70, or a diluted slow-setting  asphalt  emulsion.  The  asphalt  and  dilutant penetrate  and  coat  the  fine  particles  and  temporarily relieve the nuisance of dust. The material is sprayed at a ROA of 0.1 to 0.5 gallon per square yard. When emulsion is used, it should be diluted  with  5  or  more  parts  of  water  by  volume. Diluted emulsion dust-laying treatments usually require several applications. The dust stirred by traffic between applications eventually conglomerates and no longer rises. This is an effective treatment in a very dusty environment  where  one  application  of  asphalt  is insufficient. ROAD OILING.— Road oiling differs from dust laying in that it is usually accomplished as part of a planned buildup of low-cost road surfaces over several years. Each application may be mechanically mixed with the material being treated, or it maybe allowed to penetrate. The light oils in the road oil penetrate into the subgrade  and  tend  to  repel  moisture  absorption.  The objective in all road oiling work is to form a dustless wearing  surface,    combined   with   a   strong water-repelling   subgrade. Because soils vary widely, procedures for oiling are a matter for local trial and error, rather than scientific analysis. The amount of road oil, required in the first year of work will vary from 0.75 to 1.0 gallon per square yard. The first application is applied at the ROA of about one half of the total; succeeding applications are made in equal amounts. Road oiling treatments are placed several weeks apart,  depending  upon  the  character  of  the  asphalt  soil mat. If some breakup occurs after the first winter, light 16-23