The San Francisco call. [volume] (San Francisco [Calif.]) 1895-1913, 1895-05-04
A COMPETING PAVEMENT.

The action of the Street Committee of
the Board of Supervisors in directing the
Superintendent of Streets to prepare speci-
fcations for a pavement consisting of
basalt blocks laid in concrete is another
evidence of genuine desire for improved
paVements.
This method has been long in use by
some of the cable lines for paving the
space between the rails. Citizens who are
DESTROYS of observing the great difference
between blocks so laid and those resting
loosely on sand have only to glance at SUIT
ter street, which is but one of the thor
oughfares that has been SO treated. Be-
tween the rails the blocks are smooth,
level ana immovable, and the rest of the
street is abominably uneven Further, no
repairs of that part of the pavement lying
between the rails are ever necessary; it is
indestructible and will last until 1t is worn
through; and many years are required for
that, as basalt is the hardest and most
durable stone employed for pavements,
granite not excepted. Laid in concrete,
with care taken to leave as smooth sur
face as that which the cable companies
leave, it is incomparably superior to
more economical in the end.
In all pavements which have concrete
for base there is always the trouble which
the occasional necessity for cutting through
it presents This has been done now and
then to reach underground pipes, conduits
and sewers. Evidently basalt blocks laid
in cement would make a pavement rather
difficult to cut, but it is conceivable that a
machine could be devised which might lift
it by employing powerful leverage.
This difficulty of cutting through pave
ment having a concrete base was thor
oughly canvassed when Boss Shepard was
laying the splendid pavement in Pennsyl-
vania avenue, Washington City, and again
when London and Paris were constructing
their asphalt pavements. The decision
was made that the extra cost of cutting
through such a pavement was altogether
insignificant when compared with the
economy of the pavement itself, and that
injury to the pavement could be avoided
by cutting the trench with sloping sides
like V and reflling it with fresh con-
crete, which would form a perfect union
with the edges of the cut. 1t is presumed
that these expectations were fulfilled.
The ideal pavement used largely in
European cities, is a continuous concrete
base about eight inches thick, on which
rests an asphalt surface about two inches
thick. Sometimes cushion of softer
asphalt is introduced between the concrete
and the top dressing of asphalt. The
asphalt used in Europe is the true asphalt,
brought largely from Lake Trinidad, and
is first refined and then mixed with pull
verified granite The bituminous rock of
California is different product, but,
properly handled, is fully as good and
vastly cheaper, and its most remarkable
feature is that it generally is found properly
mixed.
In streets cut longitudinally by cable
conduits we are presented with a condition
that complicates the task of laying a con-
crete pavement. 1t is in the arch of the
pavement that much of the strength of
concrete pavement resides, and unless the
pavement between the tracks of the cable
road can be made to serve as the keystone
Of the arch pavement with concrete
base in such street might prove disap-
pointment.
In all these matters the great principle is
this: The best pavement is the cheapest.