Evening star., 1936-06-27
FINER ROAD TESTS
Federal Bureau to Have Permanent Place
and Improvements at Abingdon
Station in Virginia.

cake batter. Change one of the in
gradients ana the cake doesn't taste
the same as the time before. Con-
crete is that way, too. When mixing
concrete, great attention must be paid
to the mixing of the proper ingre-
dents"
FORMERLY materials were mea-
sured by volume. Now they are
weighed for increased accuracy. Con-
crete is more carefully compacted or
made into dense mass and is far bet
ter than earlier concretes. Engineers
have developed a system for curing
concrete after it has been properly
placed. Great care is used in mixing
the correct amount of water and in
thoroughly compacting the concrete
after it has been placed on the road.
The knowledge of these important facts
led manufacturers to produce road
machinery equipped with apparatus for
gaining exact control Of water. There
are other machines used especially for
the compacting Of concrete. e--4.
Scientific analysis has been made not
only Of concrete roads but of bitunin-
Gus as well A good bituminous road
must have stability. The two materials
which are used in this type Of road are
asphalt and tar Over at Arlington,
trial mixtures of these materials are
tested in the stability machine. The
machine indicates when rounded, soft
particles, too soft an asphalt, or too
much asphalt, are present These ma
terials must be eliminated, for. If they
are not, the result will be road which
lcses its shape under traffic.
OF recent years there has been a
great saving in the cost Of building
roads. Engineers have discovered that
roads could be laid with cheap local
materials and finished off with a sur
| face treated with tar or asphalt to
make them waterproof or dustless. Not
many years ago it was considered risky
/ to treat gravel or soil roads with a
| bituminous mixture. On some roads
the surface peeled of and became so
bumpy that a good deal of plowing up
/ or reshaping had to be done. After
years Of laboratory work and exposure
of samples to the sun, the qualities
that are necessary for a satisfactory,
enduring road were discovered. Tests
were then devised to insure the neces-
( sary characteristics in purchased ma
{ terials
! One Of the most amazing discoveries
/ made by the Bureau of Public Roads
I engineers has been the development
( of an instrument called the "pene-
/ trating eye" Bridge engineers have
/ found this mechanism helpful. When
bridge builder desires to know how
( deep he must dig to find solid rock to
use as a foundation for the support
Of his bridge, he can secure aid from
/ the Government testing grounds. One
/ Of the public roads men will be sent
/ to the scene equipped with an elec-
I trical apparatus of a convenient, port
able size, some wire and a few blast
I ing caps. The first thing that he
does is explode the caps into the
ground He then measures the time
! for impulses coming through the
/ ground to reach points at different
/ distances from the explosion 1t takes
/ only a few minutes to estimate how
much digging would have to be done
4 in order to meet rock This task would
ordinarily take several days with the
. common drilling method.