aterials of this character that are employed in highway work possess varying degrees of adhesiveness, and while they may be semi-solid or viscous liquids at ai

rtain amount of plasticity to the mixture, at the same time serving as a binding or

, according to the source from which they are obtained, as coal tars, w

actured into products that are used for dust layers on gravel or macadam roads, binders for macadam and gravel surfaces, fillers for brick, wood block and stone block pavements and for

gas from crude petroleum. It is used for the same kinds of construction as coal tar, and the

istency, but those kinds in most general use are solid or very viscous liquids at air temperature. Of the deposits that have been developed on a commercial scale, the Trinidad lake in the British West Indies and Bermude

e not always suitable for road construction, but a number of brands of road material are obtained from this source. Oil asphalts are used for dus

d materials, and likewise native asphalts and residues obtained from pet

minous materials may be classified according to consisten

eating slightly. They are used as dust layers on earth, gravel and macadam surfaces. Their efficacy dep

dinary temperature. These materials are obtained from crude petroleum or semi-solid native bitumens, in which case they are usually called mal

ums on macadam roads and as cementing agent

asphalts fluxed with petroleum oils. They are solids at ordinary temperature and must be heated to a temperature in excess of two hundred and fifty degrees b

ing expansion joints in rigid pavements and for filling the spaces

to the materials the cementing properties utilized in road construction. Mixtures of mineral aggregates and bituminous materials for various purposes are proportioned wi

bl

f Asphaltic

c Gravity Consis

C

t Solub

tu

C

nt Sol

Bit

° Nap

t Fixed

lash Point

As desired 99.5-99.9 99.5-99.

2-1.04 As desired 99.9 99.9

03 As desired 99.9 99.9 75

phalt 1.07 25 95 99

halt 1.40 7 56-57 10

1.06 Up to 135 95-97 99.5 or

t certain properties, such as specific gravity, may vary greatly among materials equally satisfactory for construction purposes. One should not be misled by apparent differences in the characteristics of materials, because these may simply be natural peculiarities which have no bearing on the usefulness of the mater

Bituminous Mater

ace Tre

deterioration of water-bound macadam when

ly strong to hold the stones in place when they are subjected to the shear of automobile tires. In finishing the water-bound macadam sur

he character of the stone, the weather and the amount of motor traffic. During the period before raveling starts, it is comparatively easy to restore the road surface at any time by the addition of screenings or clay and sand. Usually there will be a few small areas of the surface that, on account of faulty construction, will ravel or become rutted much earlier

Oiling a

ter-bound macadam, and permit traffic on it for a sufficient length of time to show any weak places in the surface and at the same time thoroughly to season the surface. If any defective places appear, they are repaired and when the surface exhibits satisfactory stability, but before it begins to rave

ad siding, or ample tank wagon service is available for long hauls so that the tank will not be held up too long. Often it is desira

are employed for spreading, the bituminous material is heated in open kettles and then spread on the surface, the quantity required usually being about one-half gallon per square yard of surface. The temperat

be of durable material, or they will quickly grind into dust. They must be free from dust when applied, as the presence of any considerable amount of dust

y done by patrolmen, who inspect the road at frequent intervals and make the necessary repairs. The patrolman is equipped with a small heating kettle, a spreading can and the necessary brushes, tampers and miscellaneous tools needed for the repair work. The place

etratio

h an extent as to increase materially the stability of the bituminous macadam over the surface treated one. It is also expected that less difficulty will be encountered in maintaining a surface of bituminous material and stone chips on this type of road than on the water-bound macadam. The extent to which these expectations have been reali

ne six inches thick placed on a well drained and thoroughly rolled earth sub

me manner as water-bound macadam, being bonded with st

, it is necessary to secure stability by appropriate construc

oller used on Grav

als employed for this class of construction are semi-solid in character and must be heated to give them sufficient fluidity for application. They may be heated in the tank wagon which is used for the application or they may be heated in separate tanks and transferred to the distributing wagon for spreading. Some kind of a nozzle or group of nozzles is employed fo

al dressing in surface treatments. These are carefully brushed into the openings between the larger stones by means of h

material, somewhat less in quantity than required for the first tr

horoughly rolled and

ge unless they are repaired promptly. The repairs are made by loosening the stone in the area affected and adding new stone as needed and then pouring on the necessary amount of bituminous material to coat

es are not too heavy. It is likely to squeeze out of shape under motor truck traffic, becoming seriously une

t Mixed

ne or gravel and a bituminous binder. Usually the bituminous material on

erves as the foundation, is either br

am. Quite often a badly worn macadam or gravel road is used for the foundation and a new wearing course provided by adding a mixed macadam surface. If

ter wearing course than the mixed macadam, and the asphaltic concrete or sheet asphalt type of surface is employed. It is necessary to finish the surface of the concrete base with some device that wi

size are likely to crush under traffic. The stone for the base course should preferably be from 3 inches down, but any available size will be satisfactory if the layer is well rolled and bonded. The base course is constructed in th

metal pipe two or three feet in diameter, around which the stone is piled. The mixing platform is usually a metal plate sometimes arranged so that it can be heated by means of a fire underneath. The bituminous material is

concrete mixer except that the drum is arranged so that it can be heated. The hot stone and the bituminous binder are put into

l be not less than two inches thick. The hot mixture is dumped and then spread by means of shovels to the approximate thickness and the sp

red with hot bituminous cement and dressed with pea gravel or stone

and considerable durability for medium traffic. It is likely to creep and become uneven when subj

haltic

f graded stone, graded sand and asphalt cement. This type is designated as aspha

thic, or Warrenite, and Topeka asphaltic concrete, respect

aded 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 mixture, varying amounts of graded sand and mineral dust, such as ground

f 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 m

ge of voids and stone of a smaller maximum size than the Bitulithic. Both types have been extensively employed for city paving, but the Bitu

road, a base course constructed of broken stone or Portland cement concrete,

ic has increased to the point where the cost of maintenance of the water-bound macadam has become exces

ure is hauled directly to the road and is dumped and spread by means of rakes. It is then rolled thoroughly while still hot, a three-wheeled roller being most satisfactory. After rolling, a seal

rties, is easily repaired and of moderate durability. It is a particularly d