The San Francisco call. [volume] (San Francisco [Calif.]) 1895-1913, 1895-06-27
FOR GOOD STREET WORK,
Asphalt and Bituminous Rock
for Use in Modern Pave
mentS.
IT MUST BE HARD AND FIRM.
Bernard Bienenfeld'S Valuable In
formation About Materials and
Ingredients.


good pavement ought to be of surprising
interest to a very large number of people
in this City at this time Everybody is
generally interested in street-paving, and
all taxpayers and real estate holders-not
to mention the army of bicycle riders-are
especially and vitality interested in the
question, What ingredients make the best
pavement?
Particularly is this true with reference
to asphalt and bitumen rock. and express
sions of opinions as to the conditions and
usefulness of these and other honest street
materials will find ready welcome in the
columns of the CALL.
Speaking of asphalt and bituminous
rock for use in the construction of pave
ments Bernard Bienenfeld yesterday said:
To briefly summarize this subject as de-
veloped in California a bituminous-rock pave
ment consists of crude material laid prac-
tically in the same condition as when quarried;
an asphalt pavement is an artificial comb1na-
ton of selected materials, refined, mixed in
definite proportions and then laid
Thcend always in view should be the pro-
duction OF a permanent, tough, smooth but not
slippery street covering that must not become
soft in summer and brittle in winter.
Both pavementS contain cementing sub
stance called bitumen, a rather loosely defined
term that means many things. Chemically,
bltumen Is natural substance composed prln-
cipally of carbon and hydrogen in certain pro-
portions. 1t is completely dissolved by chloro-
form and by carbon bi-Sulphide,
AS remarked in a previous interview, btu
men occurs III a large variety of forms, ranging
from q light volatile fluid on the one hand to
an exceedingly brittle, friable solid on the
other
me volatile huld bltumen, IKE mucllage
that is too "thin, possesses in its natural state
very little cementing power The brittle solid
Dlsumen, ike glue that IS TOO DRY" lacks en-
n1xr{ Al
ment. Like charity, the term bitumen can
therefore be made to cover a multitude of sins.
The term asphalt in this country IS taken to
mean natural substance rich In bltumen. In
this connection may be cited the asphalts OF
trinidad. Bermudas, and last but not least,
those OF California
Ihese materials when properly Tehned ana
manipulated make eXcellent aSphaItlc ceinents
for the production of artificial pavements, the
contained bitumen being of a tenacious cement
ing character and the residue being mainly
finely divided inert mineral matter
The asphaltS OF California are found prlnci-
pally in the counties OF Kern and Santa Barba-
IA. They are remarkably rich in bltumen, and
the bltumen is generally OF constant, cemen-
t1tlous and durable nature. Ihey have been
successfully used in pavements in competition
with the best asphalts employed in the Eastern
cities and have elected the warmest praise
from experts and pubic ofhclals.
But the asphalts OF California must not be
eontoun 1G with the Pltumlnous rocks OF TINS
State. The latter is found in large beds in
nearly every one OF the coast counties south or
San Francisco.
This bitumInous rock is a more or less pure
sand whose. particles are held together by q
crude bltumen, amounting usually to less
than 90 per cent of the entire mass. The btu
men has percolated into the sand from extra
neous sources in varying quantities at differ
ent points.
The sand often contains large proportion
OF earthly and clayey matter and some water.
AT one point in the quarry sample of the
rock may show on analysis 70 per cent OF BIZ
tumen ana at another point only few feet
away sample may not contaln over D per
Cent OF this cemenung maternal AGAIN, the
oltuiheh, oeing IN a crude state, may nave 100
hueh Volatie matter, or IL may De TOO irlaple
These defects are present 10 greater or less
degree IN all bltumlnous rock. Inc product
from any quarry is likely to be variable, and
unless extremely careful inspection is made of
all rock shipped the pavement laid herewith
Will be uneven IN quality, faulty and not
durable.
In laying bltumlnous rock pavements in San
francisco IL is customary 10 take the crude
rock as IL comes from the quarry (Where some
attempt Is generally made toward the selection
OF homogeneous maternal portable iron
tanks are used TO heat the rock until 1t is re-
uuceu 10 poWdery condlLon. suHclently
thlck layer OF the hot powder Is then raked
onto the foundation ana the layerl IS smoothed
ana compressed with not irons ana rollers
1t Is almost impossible, however, to select at
reasonable expense rock that will be uniform
IN character ana composition Anc even II
homogeneous IN qualIty, IL may not at all
follow that the material contains the necessary
amount OF bltumen, or that the bltumen has
the requisite cementlng property:
Inese dlfhculueS ana uncertainties are en-
tlrely absent IN tne construction OF asphalt
paVements. IN TINS CLASS or work a definite
proportion OF nXed permanent ana cement
tlous rehned asphalt IS weighed out, heated,
and then artlficialiy mixed by means OF proper
machinery, with definite proportion OF suit.
ably prepared, cIean, not sand ana powdered
limestone
Inc manner OF laying the mixture is similar
10 mat followed In laying the hot, bltumlnous-
rock powder, except that III the case OF asphalt
heaVy steam rollers are used TO thoroughly
compress the paVement-layer while still warm.
II mas oeen lound impractlcable to use this
method OF compression on bituminous rock,
which Will not hold up heavy roller until
the paYement-layer mas become cold. 1t is
then TOO late TO secure proper compression.
Practlcally all OF the 400 ODD miles OF smooth
street paVementS lana IN TINS country are OF
asphait' OUTSIDE or California but little
pltumlnous rock is lald. The asphaltc pave
ment is iar more durable smoother, hrmer and
easier OF traction than the bltum1nous-rock
pavement
Inc aspnait can be laid OF any degree OF soft
ness OF hardness, and to meet any requirement
OF traihc or OF Climate
Under proper conditions the cost of con-
structon is ABOUT the same for both kinds OF
pavement. II can be readily imagined that
the lower cost or maintenance is entirely in
/ favor OF the asphalt.