UC SOUTHERN REGIONAL LIBRARY FACIUTY
AA 001 185 733 i
Issued January 27, 1911.
U. S. DEPARTMENT OF AGRICULTURE,
OFFICE OF PUBLIC ROADS— Circular No. 93.
LOGAN WALLER PAGE, Director.
BITUMENS AND THEIR ESSENTIAL CONSTITU-
ENTS FOR ROAD CONSTRUCTION
AND MAINTENANCE.
BY
PRfiVOST HUBBARD,
CHEMIST, OFFICE OF PUBLIC ROADS.
WASHINGTON:
GOVERNMENT PRINTING OFFICE.
1911.
SRLF 0^
LETTER OF TRANSMITTAL
U. S. Department or Agriculture,
Office of Public Roads,
Washington^ D. C.^ December 5, 1910.
Sir: I have the honor to transmit herewith the manuscript of a
circular by Mr. Prevost Hubbard, chemist in this office, entitled
" Bitumens and Their Essential Constituents for Road Construction
and Maintenance." This publication presents in condensed form a
description and discussion of various bituminous materials at present
in use in road construction and maintenance. It should be of great
service in clearing up a very general misunderstanding concerning
the actual and comparative value of bituminous road materials, and
also the meaning of certain terms. I respectfully request that it be
issued as Circular 93 of this office. In view of the newness of the
subject and lack of complete data, some of the statements made may
in the future require modification. This circular will therefore be
revised from time to time in order to keep it abreast with the latest
information obtainable.
Respectfully, Logan Waller Page,
Director.
Hon. James Wilson,
Secretary of Agriculture.
eHOSO"— Cir. 93— 11 3
BITUMENS AND THEIR ESSENTIAL CONSTITUENTS FOR ROAD
CONSTRUCTION AND MAINTENANCE.
So much confusion exists among road engineers and others in-
terested in bituminous road binders concerning the meaning of cer-
tain terms as applied to these materials that" it has seemed advisable
to present in brief form the definitions of such terms as at present
used by the United States Office of Public Roads. It should be un-
derstood, however, that these definitions are at present more or less
arbitrary, owing to wide differences of opinion held by those who are
considered authorities on the subject of bitumens. Notwithstanding
these facts, it is hoped that this circular will furnish highway en-
gineers and other interested persons with a foundation for acquiring
and systematically classifying further information along the lines
herein indicated. To aid them in this matter a brief discussion of
the value of the various materials used in road construction has been
given in addition to the definitions.
Acid Sludge. — A mixture of sulphonated hydrocarbons resulting
from the treatment of bitumens with sulphuric acid; usually a waste
or by-product obtained in this manner from the purification of tar
and oil distillates. Wlien sufficiently concentrated these sulphonated
products become viscous and gunniiy. They are readily attacked
by water and are therefore unsuitable for use as enduring road
binders.
Anthracene. — A waxy crystalline hydrocarbon having the chemical
formula C14H10, found in tars, principally coal tars which have been
produced at high temperatures. Anthracene is believed to be of no
practical value in road binders.
Artificial Asphalt. — See As))lialts and Oil Asphalts.
Artificial Bitumens. — Hydrocarbon distillates and residues produced
by the partial or fractional distillation of bitumens, and hydrocarbon
distillates produced by the destructive distillation of bitumens, i)yro-
bitumens, and other organic materials, such as wood, bone, etc. Na-
tive bitumens which have been treated merely for the removal of
water and extianeous organic and inorganic materials should not l>e
classed as artificial products, but as refined native bitumens.
Asphalts. — Solid or semisolid native bitumens, consisting of a mix-
ture of hydrcK-arbons of complex structnre, largely cyclic and bridge
compounds, together with a small proportion of their sulphur and
nitrogen derivatives, but free from any appreciable amount of solid
[Cir. 0.'!] 5
6 niir.MiNs rou i{t».\i) coNsi itrci ION.
parartins, moltini;' upon tlu' applirat imi of lu'iii and cvulcutly pi'o-
duoetl by nature from i^etroliMnus coiitainiu": little or no solid paraf-
fins. Solitl or stMui>oli(l ivsidut's pi-oduci'd from i)i()l»al)ly similar
t>ils by artifu-ial prorossos are sometimes called as|)lialts. hut should
more properlv 1h' termed oil as|)halts. 'I'he more rouimou types of
native asphalts are known hy the name of tiie locality in which they
tH'our, such as Trinidad, lUMinudez. Maracaiho. Cuban. California, etc.
Native asphalts with few e.xceptions contain water, extraneous or-
ijanic or ve<i:etable matter, and inor<ranic matter, such as clay, sand,
etc. A large projiortion of these impurities is removed l)y a rough
refining process without otherwise changing the character of the
a>phalt.
Native asj)halts are usually too hard to be used as road ijinders
without tirst fluxing them with a lieavy petroleum residuum and thus
j)roducing an asphaltic cement. Artificial asphalts are, as a rule,
brought to suitable consistenc}'^ during the process of manufacture.
Asphaltenes. — A term commonly aj)plied to those hydrocarbons in
petroleums, petroleum products, malthas, asphaltic cements, and solid
native bitumens which are soluble in carbon bisulphide but insoluble
in paraffin naphtha. As a rule paraffin naphthas of different specific
gravities and boiling points dissolve different amounts of hydrocar-
bons in a given bitumen, and the heavier the naj)htha and the higher
its boiling point the greater is its solvent action. It is evident, there-
fore, that the percentage of asphaltenes will vary with the gravity
and boiling point of the naphtha, and for this reason it would seem
well to substitute for the term asphaltenes, '' bitumen insoluble in
paraffin naphtha," with a statement of the gravity of the naphtha
used and the temperatures between which it boils. The presence of
najihtha insoluble hydrocarbons is supposed to give body to the
product in which they occur and to be accountable to a great extent
for its binding value. They show no binding value, since many of
them are hard and brittle, but they produce adhesive mixtures when
fluxed with certain heavy oils. As a rule, for a given type of bitu-
men hardness increases with the percentage of bitumen insoluble in
a given naphtha. The so-called asphaltenes are not found to any
extent in native bitumens with a paraffin base, but occur principally
in asphalts, malthas, asphaltic petroleums, and in blown petroleum
residues. They vary chemically and physically with the product in
which the}' occur, and, therefore, do not represent definite chemical
compounds.
Asphaltic Petroleums. — Asphaltic petroleums, or asphaltic oils, are
petroleums containing an asphaltic base — i. e., they are capable of pro-
ducing residues very similar to native asphalts if evaporated or dis-
tilled down to the consistency of such asphalts. They contain little
' See Bitumens.
[Cir. 93]
BITUMENS FOR BOAD CONSTRUCTION. 7
or no solid paraffins and are thus differentiated from paraffin petro-
leums. Native asphalts are probably produced from such oils by
natural processes.
Asphaltic Cement. — The term asphaltic cement was originally applied
to a product obtained by fluxing an asphalt with a sufficient quantity
of heavy residual oil or flux to produce a binder of suitable con-
sistency for paving purposes. In its broadest sense it may be applied
to all semisolid bitumens of an asphaltic nature which are of suitable
consistency for use as binders in street or road construction, whether
prepared by fluxing a solid native or artificial bitumen or by reduc-
ing an asphaltic or semiasphaltic petroleum bj^ distillation or other
process.
Baume Gravity. — An arbitrary scale of specific gravity or density of
liquids, usually expressed as degrees Baume or ° B. This scale is
commonly used in connection with oil products. For liquids lighter
than water the scale begins at 10° B., which represents the specific
gravity of water, or 1.0000. As the Baume degrees increase the
specific gravity decreases. The following formulae are used in con-
verting Baume degrees for liquids lighter than water into direct
specific gravity and vice versa :
Sp. S'i'' = i3o+oB ^^ 1'^-^'' ^•
°B = ^^^^ -130 at 17.5° C.
fep. gr.
For liquids heavier than water the scale begins at 0° B., which rep-
resents the specific gravity of water, or 1.0000. In this scale the
degrees Baume increase with the specific gravity. The following
formulae are used in converting Baume degrees for liquids heavier
than water into direct specific gravity and vice versa :
145
oB = U5-J^^ at 1.5.5° C.
bp. gr.
Benzol. — A volatile colorless fluid hydrocarbon of characteristic
odor having the chemical formula CoHq. It occurs mainly in crude
coal tars and water-gas tars, and boils at 80.4° C, so that it is re-
moved in the first fraction when these tars are subjected to the
process of distillation. Benzol is an active solvent fot most bitumens.
It is sometimes called benzene, but should not be confused with
benzine, which is the term applied to the lighter and more volatile
fractions of petroleum.
[Cir. 93]
8 BITUMKNS Von KOAD lONS IIUCTION,
Bitumen, -liituiiu'iis arc mixtiirt's of iiativo ov pyro<jiMu*tic hyilro-
oarlwus and their ilorivativos, which may Im' "fuses, liquids, viscous
liniiiils, or soliils. If solids, they melt more or less readily upon the
application of heat and are soluble in earhon hisiilphide, ehloroform,
and similar solvents. They may he divided into two main classes —
(1) native hitumetis and CJ) artificial hitiimcns. Bitumens, b('in«j;
mixtures of hydrocarbons, can have no melting i)oint, although this
term is often iised to denote the tem|)erature at wMiich they soften
sufficiently to flow.
Bituminous. A term api)lic(l not oul>' to materials or objects wliich
contain bittmien. such as bituminous rock, bituminous macadam, etc.,
but also to certain pyro-bitumens, such as bituminous coal, which give
rise to the formation of l)itumens upon being sui)jected to the process
of destructive distillation.
Blown petroleum. — T^lown petroleums, which are often called blowm
oils, are ]ieir«)leum rcsiduums through which a jet of air has been
passed during or just after distillation. The blowing process causes
certain chemical reactions of a complicated nature to take place and
results in thickening or increasing the consistency of the oil to an ex-
tent depending upon its temperature and the amount of blowing which
it receives. Semisolid and solid products are thus often formed from
fluid residuums. If the oil is asphaltic or .semiasphaltic in nature,
asphaltic cements may be produced in this manner. Blown oils are
characteristically short or nonductile when semisolid, although they
may possess considerable binding value if not originally of a paraffin
nature. Blowing an oil usually increases its percentage of hydrocar-
bons insoluble in any given paraffin naphtha.
Carbenes. — A term conuuonly applied to those hydrocarbons in pe-
troleum, petroleum products, malthas, asphaltic cements, and solid
native bitumens which are soluble in carbon bisulphide but insoluble
in carbon tetrachloride. The presence of an appreciable amount of
these hydrocarbons indicates that the material in which they occur
has been subjected to unnecessarily high temperatures. Cracked oil
residuums -^how an increase in carbenes in proportion to the extent
of cracking and the formation of these products is evidently a near
step to coking. But little is known of their effect upon the value of
a bitumen for road construction, but they are generallv looked upon
with suspicion and, in certain specifications for asphaltic cements,
their prc<enco has been limited to a low percentage.
Carbon Bisulphide. — This substance, sometimes called carbon disul-
phide, is a volatile and extremely inflammable compound of carbon
and sulphur, boiling at 47° C. and having the chemical formula
CS.... Pure carbon bisulphide is a colorless mobile liquid having an
ethereal odor. It is one of the most active solvents for bitumens
[Cir. 9.3]
BITUMENS FOR ROAD CONSTRUCTION. 9
and is commonly employed for this purpose in the detennination of
total bitumen.
Carbon Tetrachloride. — A volatile noninflammable compound of car-
bon and chlorine, boiling at 76° C. It is a colorless mobile liquid
with an odor similar to that of chloroform, to which it is closely
related, and has the chemical formula CCI4. It is an excellent sol-
vent for bitumens, but is not usually as powerful as carbon bisul-
phide. It is employed in bitumen analysis for the determination of
carbenes or hydrocarbons soluble in carbon bisulphide but insoluble
in carbon tetrachloride.
Coal Tar. — A mixture of hydrocarbon distillates, mostly unsaturated
ring compounds, produced in the destructive distillation of coal.
Crude coal tar is a black, more or less viscid fluid having a gassy
odor and varying in specific gravity from 1.10 to 1.25 and sometimes
higher. It always contains a certain amount of ammoniacal water
which makes it unsuitable for use as a road binder. When reduced to
proper consistency by distillation, coal tar makes an excellent bitumi-
nous road binder, providing it does not carry too high percentages
of free carbon and naphthalene. The composition of coal tar varies
according to the coal from which it is produced and the method of
distillation. Tars produced at high temperatures contain a large
amount of free carbon and usually run high in naphthalene, while
those produced at low temperatures carry less free carbon and as
a rule less naphthalene. Low temperature coal tars are therefore
most suitable for the preparation of road binders.^
Coke-Oven Tar. — Coal tar produced from by-product coke ovens in
the manufacture of coke from bituminous coal. This process of coke
manufacture is essentially the same as that of coal gas. Larger
charges of coal are, however, carbonized in the former, and as a rule
carbonization is conducted at a lower temperature than in the manu-
facture of coal gas. The resulting tar therefore contains a smaller
amount of free carbon, averaging from 3 to 10 per cent, and is better
suited for the preparation of road binders than most gas-house coal
tars.
Cracked Oil. — The term cracked oil, as applied to road binders, refers
to petroleum residuums which have been overheated in the process
of manufacture. Overheating causes a breaking down of certain
constituents of the oil, which results first in the formation of carbenes
and later of coke or free carbon. Badly cracked residuums are be-
lieved to be inferior road binders.
Cracking. — The process of breaking down a hydrocarbon molecule
by the application of heat. This may result either in the formation
of other hydrocarbon molecules, at least one of which is unsaturated
> See Refined tar.
[Cir. 9:1]
10 UnrMKNS Ft»IJ ItoAD (ONsnU'c IMON.
niul >ho\\>. a lii«:lu'r raiio of r:irl)t)ii to livdro^t-ii than tlu* ori<2;iniil
uioKh-uK', ov t'lsi> ill tlu> ili>ni|)lioii of tli.> luolfciilc iulo its cliMuonts,
livdroiTon aiul c-arboii. In tho latlor case tho proi-rss is said to bo
lU'stnu'tivo. I'll*' nioiT Nolatilc ami cluMnicaliy stable hyib'ocarbons
can Ih» orurkoti onlv at tt'inpnat uro aboxc tlicii- lioilini,^ points. In
tlu> ilistillation of oils this is arfoniplishi'd bv c-ausin^^ condonsation
to take plaiv in the still luul nllo\vin«; tlu* condensed oils to fall back
into the residue, the temperature of which is considerably higher
than their boilin*; points. In i-arbureted water-nfas manufacture, oils
are cracked by vaporizin<; them at a nnich hi<j;her temperature than
their boilin<r points. The heavier oils will, however, crack at tem-
peratures below their normal boilin<j points, and this is particularly
true of asphaltic oils, which have to be distilled very carefully, some-
times under reduced pressure, in order to produce residuums which
are not cracked.
Cut-Back Products. — Petroleum or tar re.siduums which are cut back,
or fluxed, to the desired consistency with a distillate. Volatile dis-
tillates are employed for this purpose in the preparation of road
binders, when it is desired to have the binder increase in consistency
or become harder after application. In such cases a residuum of
proper consistency for a road binder is cut back merely for the pur-
pose of facilitating application.
Dead Oils. — Heavy oils distilled from tars at between 170° and
270^ C. with a density greater than water. These oils, if free from
naphthalene, serve as an excellent flux in the preparation of cut-back
road binders from tar pitches, which are too brittle for this purpose.
Destructive Distillation. — A process of distilling organic materials
in which the identity of the material distilled is destroyed, resulting
in the formation of tarry distillates and a coke residue.
Dehydrated Tar. — Crude tar from which all water has been removed
by distillation and mechanical contrivances known as separators.
Emulsions. — Oily substances made miscible with water through the
action of a saponifying agent or soap. Petroleums and tars may be
emulsified by this means and such emulsions, if properly prepared
from good materials, are often serviceable in the treatment of roads.
The majority of road emulsions can be considered only as dust pallia-
tives and temporary binders.
Fixed Carbon. — The residual coke obtained upon burning hydro-
carbon jjroducts in a covered vessel in the absence of free oxygen,
according to an arbitrary method. As applied to bituminous road
materials, the determination of fixed carbon would seem to be of value
in connection with petroleum and asphaltic products only. Paraffin
hydrocarbons produce little or no fixed carbon, while those of as-
phaltic character show a very considerable amount, depending upon
the percentage of asphaltic compounds present and the- consistency of
[Clr. 9.3]
BITUMENS FOR ROAD CONSTRUCTION. 11
the material. The fixed carbon determination therefore indicates
the mechanical stability and body of such materials. It is not, how-
ever, an extremely accurate determination and should not be too
strongly relied upon. Since fixed carbon is a product formed by
ignition, it should not be confused with free carbon, which is a
material already existing in suspension. The presence of any consid-
erable quantity of free carbon vitiates a fixed carbon determination.
Flux. — As aj)plied to road binders, this term covers fluid oils and
tars which are incorporated with asphalts and semisolid or solid oil
and tar residuums for the purpose of reducing their consistency.
Fluid petroleum residuums are commonly employed as fluxes in the
preparation of asphaltic cements. A good flux produces an abso-
lutely homogeneous bituminous mixture. Both petroleum and tar
fluxes will produce such mixtures with native and artificial as-
phalts, but most fluid petroleum products will not flux tar pitches
satisfactorily.
Free Carbon. — Organic matter in tars which is insoluble in carbon
bisulphide. This material is an inert black powder, which is held in
suspension by the tar proper, and probably consists, not only of free
carbon, but also of hydrocarbons extremely rich in carbon. It has
no binding value and serves no useful purpose in a road binder other
than to act as a filler. It gives the tar in which it occurs a false
consistency, reduces the binding capacity of the tar, and probably
interferes with its penetration into and absorption by the road stone
or road surface. The maximum allowable limit of free carbon in
road binders would seem to be about 20 per cent.
Gas-House Coal Tar.^ — Coal tar produced as a by-product in the
manufacture of illuminating gas from coal. The modern gas-house
coal tar is usually produced at high temperatures and therefore
carries a percentage of free carbon varying from 20 to 30 per cent
and higher. Unless it is produced at low or medium temperatures
and contains less than 20 per cent free carbon, it is not well suited for
the preparation of a dust palliative or road binder by direct distil-
lation. High-carbon tars may, however, be combined with low- .
carbon tars in such proportion as to produce, when distilled to proper
consistency, excellent road binders carrying less than 20 per cent free
carbon.
Gilsonite. — A very pure solid native bitumen possessing many of the
characteristics of asphalt. It differs from most of the native asphalts
by being more brittle, having a higher melting or softening point,
and being much less soluble in 86° B. paraffin naphtha. When fluxed
with certain petroleum residuums it j)r()duces excellent asphaltic
cements. In the preparation of road binders it is extensively used
for the purpose of reinforcing blown oils, with which it combines to
1 Sec Coal tar.
[Cir. 93]
12 BITUMENS FOU KOAD fONSTRrCTlON.
fi)rm rublHM'v stMiiisidiil mixture-. Such |irr|):u:iti()ns arc Miiuotiim's
termed mineral rubber.
Grahamite. A pure solid iiativi« bihuiitMi. black and brittle, which
diH'> iu)t null roailily, but iiitunicsccs at hiirh temperatures. It is
tlitferentinted from ixilsonitc and the ii:i(i\i' asphalts by the fact
that it is almost insoluble in paratlin naphtha. It has been produced
at hi«rh temperatures, as e\ idenced by the percentage of cnrbenes
which it contains, and some varieties closely approach the pyro-
bitumens in characteristics. It has been used to s<ime extent in the
preparation of asphaltic cements, but up to the present has been little
u.sed in the manufacture of road binders.
High-Carbon Tars. — Tars containinir a hiirh percentaije of free car-
I'on -al)ove I'O per cent. Iligh-carbon tars are produced at high
temperatures during the destructive distillation of coal and are of
inferioi- <|uality for use as dust palliatives and road binders.
Hydrocarbons. — Chemical compouiuls comjiosed of the elements
hydrogen and carbon. There is practically an unlimited number of
such compounds, which vary greatly in physical and chemical charac-
teristics. Complex mixtures of hydrocarbons constitute by far the
greater proportion of all bitumens.
Low-Carbon Tars. — Tars containing a low percentage of free car-
bon — less than 10 per cent. Low-carbon tars are produced at com-
paratively low temperatures during the destructive distillation of
coal, and also In' cracking oil vapors during the manufacture of car-
bureted water gas. As a rule they are more suitable than high-
carbon tars for use as dust palliatives and road binders, or for the
preparation of such substances.
Malthas. — Malthas are very viscous semiasphaltic or asphaltic native
bitumens holding an intermediate position between the petroleums
of an asphaltic nature and the native asphalts. As a rule they possess
excellent binding properties. They constitute the binding material
of many bituminous rocks or rock asphalts, and in this capacity often
.serve as valuable road binders. Many malthas have a tendency to
harden rapidly when exposed to atmosjiheric conditions, and this prop-
erty, while accountable for an increase in binding value, makes them
unsuitable for use as a flux in the preparation of asphaltic cements.
Malthenes. — A term commonly applied to those hydrocarbons in
petroleum, petroleum products, malthas, asphaltic cements, and solid
native bitumens soluble in both carbon bisulphide and paraffin naph-
tha, but not readily volatile at temperatures lower than 108° C. (325°
F.). This class of hydrocarbons serves as a valuable permanent flux-
ing medium for the so-called asphaltenes or naphtha insoluble bitu-
men in asphaltic cements, giving the cement any desired degree of
.softness when present in the right amount. It is evident, therefore,
that the consistency of asphaltic bitumens, and particularly stable
[Cir. 931
BITUMENS FOR EOAD CONSTRUCTION. 13
asphaltic cements, is largely dependent upon the relative proportion
of naphtha soluble and naphtha insoluble hydrocarbons. The same
objection to the use of the term " asphaltenes " ^ applies to the use of
the term " malthenes.''
Mineral Rubber. — A term sometimes applied to artificial bitumens
of rubbery consistency, usually composed of a mixture of gilsonite
and blown petroleum residuum.
Naphthas. — Mixtures of hydrocarbons of low boiling points occur-
ring rarely in nature, commonly obtained from the fractional dis-
tillation of certain bitumens. Wlien this term is applied to low-boiling
coal-tar distillates, it is usually prefixed by the words " coal tar."
The word " naphtha " by itself is generally applied to low-boiling petro-
leum products. Different grades of naphtha are dijfferentiated not
only by their boiling points but also by their specific gravities, which
are commonly given in Baume degrees. Those of very low boiling
points and specific gravities are called petrolic ethers. Naphthas
vary not only in the two properties above mentioned but also with the
type of petroleum from which they are obtained. Those derived
from paraffin petroleums are quite different chemically from naph-
thas obtained from asphaltic petroleums. The former are much less
powerful solvents for asphaltic substances than the latter. Paraffin
naphtha is used as a solvent for the separation of certain classes of
hydrocarbons in asphaltic substances.
Naphthalene. — A solid crystalline highly volatile hydrocarbon oc-
curring principally in coal tars and having the chemical formula
CioHg. Its presence in excessive quantities in road tars is believed
to be detrimental, as it possesses no binding value and gradually vola-
tilizes from the tar, leaving it hard and brittle.
Native Bitumens. — Mixtures of hydrocarbons occurring in nature,
which may be gases, liquids, viscous liquids, or solids, but if solid melt-
ing- more or less readily upon the application of heat and dissolving
in carbon bisulphide, chloroform, and similar solvents. The native
bitumens that are of use as road materials are petroleums, malthas,
asphalts, and other solid products such as gilsonite and grahamite.
Native bitumens often contain impurities such as water, inorganic
matter in the form of clay, silt, sand, etc., and extraneous organic
or vegetable matter.
Oil Asphalts. — Artificial oil pitches or asphaltic cements produced as
a residuum in the distillation of semiasphaltic and asphaltic petro-
leum. Many of these products are blown and are therefore known
as blown oils.
Oil Pitches. — More or less hard oil asphalts.
Oil Tars.^ — Mixtures of hydrocarbon distillates, mostly unsaturated
ring compounds, produced in the cracking of oil vapors at high tem-
1 See Asphaltenes. ^ gpg Bitumens. ^ gee Water-gas tar.
[Cir. 93]
14 BirrMKNs FOR uo.M> coNsrurcrioN.
poratmvs. Oil (Hi's are usually l>v-|>n)«ln<'ts of (lip lUiunifacluro of
oil pis or carluirottvl waltM* pis.
Paraffin Naphthas.- Naphthas consist in<x of a niixturo of lijjht vola-
tiK' hyilnH-arlions of (he parallin siM'ios. oi-dinarily ohlainod as lijj:ht
tlistillatos of paraflin potrolouni.
Paraffin Petroleum. — PotroloMni the base of which is composed prin-
cipally o{ the i)araf]in or open-chain series of hydrocarbons; it is
thus differentiated from asphallic petroleums which are composed
largely of cyclic or rin<; hydrcK-arbons. Paraflin petroleums and the
uiuiltereil residiies pnxluced by their distillation are of inferior value
as dust palliatives and road binders.
Paraffin Scale. — Solid jiaraflins recovered by distillation and pre-
i ipitaiionof thedistillatesof petroleumand similar materials. The per-
centajre of paraffine in bitumen is usually determined in this manner.
Paraffine. — The term paraffine covers a number of gi'easy ciystalline
hydrocarbons of the paraffin series occurring as dissolved wax in cer-
tain cla.sses of petroleum. ^Mien these products are recovered from
petroleum, they constitute the commercial product paraffine. Par-
affine is believed to be detrimental to road binders in which it occurs,
and it is certain that its presence in excessive amounts indicates infe-
riority in the binding value of the material. It is probable, however,
that heavy liquid hydrocarbons of the same chemical series as solid
paraffine exert a much more injurious effect.
Petrolenes. — An ambiguous term sometimes applied to those hydro-
carbons described under malthenes, which are soluble in carbon bi-
sulphide but insoluble in paraffin naphtha, and sometimes to hydro-
carbons in petroleum and petroleum products volatile at or below
103° C. (325'' F.). Owing to misconceptions which may occur, it
would seem advisable to eliminate the use of this term.
Petroleums. — Petroleums, or mineral oils, are fluid native bitumens
of variable composition, depending largely upon the locality in
which they occur. There are three general types of petroleum found
in the United States: (1) Paraffin petroleums, (2) semiasphaltic
petroleums, and (3) asphaltic petroleums. Paraffin petroleums occur
mainly in the eastern part of the United States and are typified by
the Pennsylvania oils. The semiasphaltic variety occurs in the south-
ern and middle western parts of the United States. Texas is one
of the main sources of this type. Asphaltic petroleums occur in the
western part of the United States, particularly in California.
Petroleums, if of semiasphaltic or asphaltic character, may make
excellent dust palliatives and road binders when properly treated.
Petrolic Ethers. — Very light volatile naphthas obtained from petro-
leuni.
Pitches. — Semisolid or solid residues produced in the evaporation
or distillation of bitumens. This word is often prefixed by the name
[Clr. 93]
BITUMENS FOR ROAD CONSTRUCTION. 15
of the material from which it is derived, such as oil pitch, coal-tar
pitch, etc. As a rule the term pitch is confined to the harder re-
siduums, most of which are too hard for use as road binders unless
fluxed with a more fluid product.
Pyrobitumens. — Mineral organic substances which are but slightly
acted upon by the solvents for the bitumens, but which, upon being
subjected to destructive distillation, give rise to the formation of
bitumens. Pyrobitumens are derived in nature both from bitumens
and direct metamorphosis of vegetable matter. Among the former
class may be mentioned Albertite and Wurtzilite, and among the
latter, peat, lignite, and bituminous coal.
Pyrogenetic. — Originating from the action of heat. Coal tar is thus
a pyrogenetic bitumen.
Reduced Petroleums or Reduced Oils. — Residual oils produced from
crude petroleum by the removal of water and the more volatile oil
constituents, without chemically altering the base by cracking or other
means. These residues are often made by distilling the crude oil
under reduced pressure. Such products are of little value for road
treatment unless formed from semiasphaltic or asphaltic oils.
Refined Tar. — A more or less viscous tar which is produced by
evaporation or distillation of crude tar until the residue is of the
desired consistency. This term also includes blown tars and cut-
back products produced by fluxing tar pitches with volatile or non-
volatile distillates. Refined tars are of value both as dust palliatives
and as road binders in the treatment of macadam roads. Their
binding value is proportional to their hardness within certain limits.
Residual Petroleums or Residual Oils. — Heavy viscous residues pro-
duced by the evaporation or distillation of crude petroleum until at
least all of the burning oils have been removed and often some of the
heavier distillates as well. Residual oils grade into the artificial
asphalts and oil pitches as their hardness and viscosity increase. The
more fluid products, if obtained from semiasphaltic or asphaltic
petroleums, serve as excellent dust palliatives and semipermanent
road binders for the surface treatment of roads. The more viscous
products are often suitable for the surface treatment of roads if ap-
plied hot, but are seldom of value in road construction unless pro-
duced from semiasphaltic or asphaltic oils.
Residual Tars. — Heavy viscous residues produced by the evaporation
or distillation of crude tar until all of the light oils have been re-
moved. Residual tars grade into the tar pitches as their hardness
and viscosity increase. If they do not contain an excess of free
carbon, they are as a rule well adapted for use as binders in the con-
struction of macadam roads.
Rock Asphalt or Bituminous Rock. — A term applied to a great variety
of sandstones and limestones more or less impregnated with maltha.
[Cir. 93]
l(') Uni'MKNS Foil HOAl) I'DNSTIirt'TlON.
I)t'pik^ils of !«)H'h miiti'riiil nvc widolv (li.-.tnl>iil»'il ovov tho I'liited
Siatt'.< iuul varv from nuk whifh is frinltlf ami wholly drpiMulont
uj)oii tilt' bitumen to hold the iniiiiMid l"i:iu:iu»'ii(s tojiri'tluM' to solid
riH'k lmviii«: nioivly its intt>rs(iiTs lilK'd with hitiiiiuMi, Tlu' fonuer
ty^K" is i>f valiio for uso as a surfan* hiiulor in (he eonst ruction of
roads when the maltha shows jjood bindin*; value and amounts to not
le-^ thun (■' |H r <«Mit of tlu' wciijht of ro*'k asphalt.
Semiasphaltic Petroleums. Scmiasphallic petroleums or semi-
asphiiltie oil>- are petroK'ums containiuir a seuiiasphaltie base, i. e.,
petroleums whose residues j)rodueed l)y e\aporation or distillation,
while itunpost'd mainly of asphalt ic hydrcKarbons, contain also a cer-
tain pen^entrt^e of paralVm wax. They thus show a mixed base. If
tlu'ir percenta<j:e of heavy parallin hydiocarbons is not excessive, they
may be made to protluce ^"o<k1 dust preventives and road binders.
Short. — A tvrm applied to l)ituminous materials which are non-
thu'tile.
Tar Pitches. — Semisolid or solid residual tars. Owing to the gen-
eral brittlene.ss of tar pit<jhes, only the softer varieties are of value
in their natural condition as road binders. The harder pitches may,
however, be used for this purpose if fluxed to suitable consistency
with heavy or dead oil distillates of tar.
Tars. — Tars are artificial or pyrogenetic bitumens produced as dis-
tillates by the destructive distillation of bitumens, pyrobitumens, and
other organic material.
Water-Gas Tars. — ^lixtures of liydrocarbon distillates, mostly unsat-
urated ring compounds, iDroduced by cracking oil vapors at high
temperatures in the manufacture of carbureted Avater gas. Crude
water-gas tar is a thin, oily liquid having a specific gravity lying usu-
ally between 1 and 1.10. As a rule it contains a considerable quantity
of water, which is. however, largel}' removed by mechanical devices
before the tar is placed upon the market. This water is not am-
moniacal, as in the case of crude coal tars. The composition of water-
gas Uir varie^s with the character of the oil which is carbureted and
with varying conditions attending the carbureting process. It always
shows a low percentage of free carbon, usuall}^ less than 2 per cent,
and contains little or no naphthalene unless previously used for scrub-
bing coal gas. Crude water-gas tar has practically no binding value
and is serviceal>le only as a dust palliative in the surface treatment
of roads. When reduced to proper consistency by distillation, how-
ever, it shows certain desirable properties for use as a road binder
both for surface treatment and macadam construction. AVater-gas
tar may also be used in the preparation of road binders from high-
carbon coal tars. "When this is done, the two crude tars are mixed in
such proportion that when distilled to the desired consistency the mix-
ture will contain le.ss than the maximum limit of free carbon allowable.
[Cir. ft.l]
o