The San Francisco call. [volume] (San Francisco [Calif.]) 1895-1913, 1895-06-04
GIVE ASPHALT A CHANCE,
That Is What Engineer Nc
Cullough Says Should
Be Done.
Give 1t an Equal Trial With
BItuminous Rock.

Ernest Mccullough. consulting engineer
of the Merchants Association, says he is
not prepared to admit that asphalt pave
ments are superior to bituminous rock
! covering for streets. He makes an inter
esting comparison of the two pavements:
Asphalt is variety of bitumen and is
obtained in many parts of the world, " said
he. "In the valley of the Rhone, in France
| and Switzerland, and in parts OF Italy,
Sicily, Spain and Hanover, there are large
beds of sandstone thoroughly impregnated
| with bitumen, and from these beds most of
| the asphalt paving used in Europe is OBJ
| tanned. On account of the fneness of the
| stone streets paved with it are rather slip
| perry in wet weather.
In Trinidad is a large lake of asphalt,
which is mined in its natural state, and
after refining, to drive out the impurities,
| it is shipped to other countries and mixed
with sand and carbonate of lime, to make
| an artificial pavement similar to that made
| by the natural bituminous sandstone of
| Europe. This asphalt pavement is not SO
| slippery as the former, as the sand mixed
with It is coarser than the natural sand
stone. Pavements of Trinidad asphalt are
very popular in Eastern cities.
california is the only State in the
quantities, but it is nearly all in an impure
state, being mixed with sand, mica, loan
| and other earthly materials. This impure
asphalt is commercially known as btu
minous rock, and is what we are used to
seeing laid on our streets. The only objec-
ton to it is that it is a paving material
mixed in natures laboratory and therefore,
is not uniform. The same quarry may
yield good and bad rock. The getting out
of good rock is a matter of Judgment, and
even the best men are not always correct
in their opinion of the quality of the rock
before it is laid.
Some poor rock has been laid on the
streets of San Francisco, and the specifica-
tons at present under consideration will
not help matters, but will rather tend to
make them worse. The clause calling for
the rock to be laid in its natural state ON
the street where it is to be laid is the most
objectionable for many reasons, the prin-
cipal one being that it precludes careful
selection and the rejection of poor rock.
After contractor has hauled his rock to
the street where it is to be laid, he is apt
to try to work in all the material, even if
it is not all good. The treatment so many
object to is sometimes necessary. Bitumin-
Gus rock is even less slippery than the arti-
hc1al asphalt pavement as rule, and may
be laid on sleeper grades
"The bituminous rock being a natural
product and therefore of uneven compost
ton, it is extremely difficult to draw up
specifications which will result in uni
formly good work. It is q case where the
integrity of the contractor must be taken
into account. With the present low prices
for such work it is impossible for firm to
exercise the proper selection of material
and make any money. 1t must all 60 in,
and instead of getting good job with good
material an average job must be taken
with average material. Asphalt pavements
being artiticially mixed, it is possible to
draw up specifications which will insure
the same standard of work on all streets.
1t should therefore be more generally used
in California. Much of our California
asphalt is refined and sent East to adulte-
rate Trinidad asphalt. In fact, it has
achieved such reputation there that many
cities use asphalt from both California and
Trinidad. with no odds TO either.
at seems an anomaly that in this State
so little is thought of asphalt pavements
and that bituminous rock is so greatly
preferred. In San Francisco no specifca-
tions are in existence for asphalt paving
and only bituminous rock is provided for.
1t seems fair play would demand that
asphalt be given show. 1t is for this rea-
son that the Merchants Association will
endeavor to have specifications adopted
for asphalt pavements and put them on an
equal footing with bituminous rock
81 am not prepared to say which ma
terial is best. Both have their good quail
ties and both are therefore entitled to con-
sideration. Frankly, if l had charge of a
piece of paving and had to choose between
asphalt and good quality of bituminous
rock the price alone would influence my
selection"