Part 12 (1/2)

Asphaltic concrete is a naraded stone, graded sand and asphalt cenated as asphaltic concrete because of the analogy of the mixture to Portland ceeneral types known as bitulithic, or Warrenite, and Topeka asphaltic concrete, respectively, the differences being in the nature of the mixture

=Bitulithic or Warrenite=--The stone eraded down from a size about equal to one-half of the thickness of the wearing course, and stone passing a 1-1/4 or 1-1/2-inch screen is usually specified Froraded down to the finest particles produced by the crusher The range of sizes of stone will vary with the source of the supply, and in order to secure the desired density in the raded sand and round limestone or Portland ce mixture contains less than fifteen per cent of voids, and to this carefully graded h asphalt ceether the particles

=Topeka Asphaltic Concrete=--In this type of asphaltic concrete, the raded sand and of broken stone of such size that all will pass a one-half-inch screen and graded down to the fine dust produced by the crusher To this mixture is added about nine per cent of Portland cement or limestone dust The voids in the mixture are usually about twenty-five per cent

It will be seen that the essential differences between the Bitulithic and Topeka types are these: the Topeka type contains a larger percentage of voids and stone of a smaller maximum size than the Bitulithic Both types have been extensively e, but the Bitulithic and Warrenite types have also been used to sohways The Topeka type has been used but little for rural highways

=Foundation=--The foundation for the asphaltic concrete may be an old macadam road, a base course constructed of broken stone or Portland ce used much more extensively than either of the other types

So water-bound ravel roads when the traffic has increased to the point where the cost of maintenance of the water-boundsurface is repaired and the cross section is restored, or possibly flattened so the Surface=--The stone, sand and asphalt cement are heated to the required temperature and cohly mixed by a mechanical mixer The mixture is hauled directly to the road and is duhly while still hot, a three-wheeled roller being , a seal coat of hot asphalt cement is spread over the surface and covered with hot stone chips about 1/4 inch in size The surface can be opened to traffic immediately after the surface has been completed

=Characteristics=--The asphaltic concrete surface is of excellent riding properties, is easily repaired and of moderate durability It is a particularly desirable surface for pleasure auto and for horse drawn traffic

CHAPTER XI

MAINTENANCE OF HIGHWAYS

Proper hways is equally important with proper construction With nearly all types of road construction, the need for maintenance arises soon after the surface is placed under traffic and is continuous thereafter The nature and a the several types of surface and the organization suitable for a systehill depend to a considerable extent upon the kinds of surfaces that are to be maintained

The upkeep of a road may be conveniently considered as of two kinds, viz, (1) that which has to do with the wearing surface and earth shoulders or berms upon which there is some traffic and (2) that which has to do with the side ditches and drainage structures and keeping the roadside in presentable condition Both kinds of work are usually carried out by the saanization, but whereas the nature of the work indicated under (1) will vary with the type of wearing surface and with all variations in traffic, that which is indicated under (2) will be nearly constant in any locality

ORGANIZATION FOR MAINTENANCE

Maintenance of highways is preferably under the administration of the same authority as construction and when an ihway Department, the completed improvement is ordinarily maintained under the state authority If the improvement is made by county authorities, the maintenance is also carried out under county authority

The nature of the organization of maintenance forces is dependent upon the kind of roads to be cared for and must of necessity be varied in any instance as conditions des or patrolmen are employed and often both are used on the same road system

=Patrol Maintenance=--Where this systehway systehteen e of each district He is provided with all of the necessary tools and materials required in his district and perforhway He should work under the direction of the county engineer or the district engineer for the state highway department, because his work involves the use oftechnical supervision

=Gang Maintenance=--Themay be employed for some types of road surface in lieu of the patrolman or with other types of surface may be employed to supple consists of three to ten men and is furnished all of the tools and materials required for the particular kind of work they do Ordinarily the gang goes over the roads assigned to it once each season and perfor more work than the patrol like that of the patrol supervision