Deseret evening news. [volume] (Great Salt Lake City [Utah]) 1867-1920, 1910-01-27

''N~hi oii tit iOCh gives
isfactory results on account of the con-
tinuous and unavoidable washing
away or blowing away OF the detritus
worn from the rock. This amount must
De supplied continuously from the or
dinary wear which rock will yield to.
The wear should be proportional to the
tratnc. not being too great so that a
surplus remains on the road, not too
small 80 that more would wash away
that Is formed. This leads US to the
conclusion that where the tonnage car
ried by road is great. the stone of
which the road is made should be more
resistant to wear and where the ton
mage Is less, the stone should be less
resistant, and where the tonnage Is
but small, the rock could be chosen for
cheapncss rather than for strength.
1t is we'll known that some kinds OF
earth make very good roads, yield
ing but little mud in winter and
but little dust in summer. other kinds
OF earth is famous for the Elasticity
and adhcrcnt quality OF Its mud;
plastic when a wheel load comes on II.
adherent when the load tries to come
off 1t. Such material. geologists tell
us. in fact nearly all of the soil, is
result of wearing away OF the various
kinds OF exposed rock. 1t Is certain
that none OF us farmers would choose
the kind Of rock for road-building that
yielded the mud OF which many OF
our mud lakes were formed If we
knew what We were doing On the
road. We desire the rock dust to be
adhercnt, that Is, to adhere to itself
and to the unworn rock. we desire 1t
10 fill the voids at the surface holding
the rock In place. and not be picked UP
by every wheel that travels over 1t i'll
winter, nor sucked up by many rapid
wheel passing over II in summer. All
of our sedimentary rock has been
formed from sand and silt by pressure
and moisture. This sand and silt had
been formerly worn from still older
rock, and is now recementcd. Does
the rock dust OF today tend to recc-
ment? Does some rock dust recement
better than others? II SO, then We
should choose for our road a rock
yielding a dust which recements well
under the pressure of the wheel and
moisture from the air. and not ono
that mixes up into plastic putty.
MUST LEARN BY EXPERIENCE.
From the preceding arguments. 1t is
plainly evident that 1t requires an en-
gineer OF considerable experience 10
properly estimate the traffic on the road
being careful to properly estimate the
future. and then from his knowledge
of rocks and road-building. choose the
one best suited to the conditions Is
there any way by means Of which we
can educate ourselves, who have had
little experience in the building of
roads, and little experience with rock
placed on the roads, Can we educate
ourselves by studying the experience
of others. their successes and failures?
Can we apply the test to rock as they
apply them determining which Is good
rock as they arc able to- and which
Is poor rock, and thus have our judg-
ment infallibly led to accept only good
material and to reject only poor ma
tcrial?
TESTING MATERIALS.
This leads us to a study of the tests
that are made on broken stone which
VIII assist us in estimating the be-
havior of the rock when placed on a
road, Briefly. these tests are an abra-
sion test to determine the per cent or
co-efficicnt Of wear, an impact test
to determine the toughness of tho
stone. another impact test on the
moulded rock dust to determine. the
relative recementing quality of the
detritus, grinding test to estimate the
hardness and the determination of the
nineralogical composition These tests
are standard and easily made; for cx-
ample. the abra sion test consists of
taking about 90 pieces of rock Weighing
IL pounds and placing 1t in the stand
ard abrasion cylinder and then rotating
the cylinder 10000 revolutions at the
rate of about 80 per minute Then sift
out all dust that will pass a lis inch
mesh sieve. The weight of detritus un-
der lis in grams per kiloeram di-
vided into 400 is called the co-efficient
of wear. This gives a series of num-
bers for various rock which indicates
their relative wear. The impact and
hardness tests are similar in that thew
are imperial standard tests giving
numbers which may be compared. The
details of these tests 1 shall not ex-
plain
Now having gathered your samples
from the different quarries and from
dinerent parts of the same quarry. and
MADE the tests and obtained your re-
suits. which are series of numbers
how shall we interpret these results so
as to reject the bad and accept the
good? In answer to this question. 7
can do no better than to quote from a
recent paper by r. S. Greenman. IN
Transactions of the American Society
for Testing Materials, vol 8. page 5SS
Speaking of New York state. he SAYS:
The great state of New York has been
come well established in the construc
ton OF S50O00.000 worth of new roads.
experience has already taught tina.
greater care must be taken in
the selection of road material
The real question before us is NOT
to make tests and secure compari-
sons, but, having secured the results.
how 10 draw limitations in the selec-
ton of stone that will be fair to both
the state and producer. In other prod-
ucts We have standard requirements.
but i'm this field we have vet to
develop just limitations Based on
standard tests II would be practical
" impossible to draw up a general
specification that would permit the
use of a good limestone and that
would at the same time shut out a
poor trap-rock or q poor svenite.
1T may be necessary that in each
case local conditions shall first be
considered and then a specification
made to fit these conditions. With a
large amount of roads about to be
constructed. this probably would not
be entirely satisfactory. 80 II specifica-
tions can be drawn covering general
conditions and applying to the gen.
eral classes of road construction. bet-
ter results must be the outcome OF
such specifications. For the purpose of
discussion, IT may be well to divide
the roads into three general classes.
Those of first class or grade, will be
those that are fnterurban' or trunk
lines which are subject to heavy
traffic and wear and which shall be
made the best possible. with cost a
subordinate consideration: the roads
of the second grade Will be such roads
as are subject to the traffic of an
average popular country road, and
which shall be constructed with due
4