Sacramento daily record-union. [volume] (Sacramento [Calif.]) 1875-1891, 1890-01-31
STREET COVERINGS.
RELATIVE MERITS GF VARIOUS SUB
STANCES CONSIDERED.
Bituminous Rock Claimed to be Far Pre-
ferabIe to Gravel-CoaI-Tar Not
Good Substitute for Cement.

EDS. RECORD UNION: Concerning the
suggestion in last Sundays issue, for using
coal-tar and gravel as a concrete base for
streets, nothing is said of the manner of
preparing it, and perhaps few words in
that direction may be acceptable. Cosl-tar,
as it comes from the gas works, is not ad-
hesive to any great extent. 1t is some
what penetrating, but even that property
disappears rapidly under evaporation, like
coal oil applied to wood it has no lasting
properties if left exposed to the atmos-
phere.
By cooking or boiling its penetrating
properties become less, but its adhesiveness
is greatly increased. Without the neces-
sary amount of cooking, you cannot make
it harden by the addition of any amount of
sand, ashes or other matter. There must
be an evaporation of the oils and volatile
properties before it will harden.
These properties are got rid of quickest
by cooking When cooked or boiled suffi-
GENTLY it is not necessary TO add sand or
ashes to make it harden, no more than it is
to put something into maple syrup to
make it harden into sugar. Coal tar can
be cooked into any degree of crystalliza-
ton. When the oils have thus been ex-
tracted its adhesiveness has greatly in
creased, and by adding stone or gravel you
can have concrete which, when cold, is
very hard. In this manner it becomes
useful.
Everybody knows that hundreds of miles
Of sidewalk have been laid in this State of
this concrete, with one very important ex-
cept1on in the manner of preparation. As
pEaltum, which is the residuum of what is
called by some naphtha tar, after the oils
have been extracted, either by distillation
or evaporation. has much more adhesive
ness than coal tar in any condition it is
also heavier substance, more durable, and
less easily destroyed by water or evapora-
ton. Hence, in all sidewalks of this kind
asphaltum was the principal ingredient,
only small proportion of coal tar being
used, merely to hasten the process Of liqui-
flying the asphaltum, which in its market
able state is quite hard, the oils having
evaporated during the long period since
its outflow in the form Of naphtha tar, or
heavy-grade petroleum. Consequently
these sidewalks were called asphaltum
sidewalks.
Santa Cruz bituminous rock" is formed
by the OVERLOOKING of naphtha-tar springs,
which has saturated large bodies of sand
and gravel, and hardened as the oils
evaporated. Its practice bility for pavement
was not generally known until few years
back. 1t is a natural concrete, requiring
the addition of neither sand nor bilumen.
Il only needs cooking and thoroughly mix
ing, before laying, and costs on the Car at
Santa Cruz IS so to 81 per ton. This con-
crete is not so fine or so firm as the arti-
fetal one of the past but is cheaper. 1t
can be laid down in more flexible state
without being sticky, and is quite as dura-
BILE; its decay being caused by the evapora-
ton of the oils it contains, leaving the sur
face more brittle and more susceptible to
damage by wear Such a concrete makes a
better covering for a street than cement
and stone, as it is more flexible, less noisy,
and cleaner; though not so good foUnda-
ton.
Stone and cement in suitable proportions
make an imperishable concrete, and if four
to six inches thick, is capable of bearing
any weight that can be hauled on a truck,
if the tires of the truck wheels have the
proper width. Whether the adhesiveness
of cement is less or greater than asphaltum
the only way it could be damaged would
be by a greater weight upon it than it could
bear, as water would not affect it after it
was once dry. The economy of road
building is in the foundation, as the sur
Mace can be more easily and cheaply re-
paissed or renewed.
A rock and cement concrete four to six
inches thick, laid roughly, simply pounded
or rolled down, will cost less than one of
equal strength of asphaltum, and undoubt
eddy is more secure and durable.
The suggestion in the article referred to,
of putting gravel covering over concrete,
would never do in town where the SYM
metry Of street is "a thing of beauty" 1t
would do in country lane where good
track the width of one wagon is all that is
required, and, being placed on the center or
crown of the street, would soon wear down
hard, and to that extent would be better
than clear mud.
Gravel will not stay where you put it,
unless the surface is level, and the same
may be truthfully said of cobbles. You
cannot roll it down on a curved surface so
it will stay; it will crawl from the crown
to the gutter. As the result of forty years
experience in San Francisco and Oakland,
the prevailing public sentiment is in favor
of stone and cement concrete base covered
with Santa Cruz bituminous rock. Oak
land, however, had the advantage of hard
worn macadamized streets, which, to
great extent, took the place of the concrete
base. One might ask why we could not
use the stone here without the cement. If
broken stone alone was used, it would re-
quire depth of eight to twelve inches and
rolled with heavy roller and all traffic
kept of until completed with the bitumin-
GUS rock. The extra quantity of stone re-
quired and the expense of rolling down
would more than equal the cost of the &C.
ment, and it would not be SO good in many
resuects F. r BPOWN