La Junta tribune., 1917-05-10
OF
CONCRETE ROADS
Rapid Increase Of Mileage In
Recent Years.
BOTH DURABLE AND SMOOTH

toSaHta9et ana 0baoNSUtSSSs Soh-
trasted In a New Bulletin Of the De-
partmsnt Of Asrieulturs-Advies For
Construction Of Concrete Highways.
The mileage OF concrete pavement In
the United States has increased rapid
ly. and II is likely to continue TO In
crease. according TO u new bulletin OF
the department OF agriculture. This
bulletin gives the estimated amount OF
concrete pavement In the United States
In 1914 as 100000 square yards. In
1909 1t was only 3Gi,o0o square yards.
The principal advantages of concrete
pavements which have led to this in
crease In popularity are said to be:
Durability under ordinary traffic con.
ditions.
A smooth, even surface, Offering little
resistance.
Absence of dust and ease with which
II may be cleaned.
Comparatively small cost of maiDte-
nance until renewals are necessary.
Availability as base for another
type of surface II desirable.
Attractive appearance.
The disadvantages OF concrete as a
road surface are:
Its noise under horse traffic.
The wearing OF the necessary Joints
In the pavement and the tendency 10
crack. with Its consequent rapid de-
terioration.
The difficulty OF repairs when these
become necessary.
In the past efforts have frequently
been made TO overcome these objec.
tions TO certain degree by covering
the concrete pavement with q bitumi-
nous wearing surface. At the present
time the specialists In the department
hold that this cannot be economically
justified. although 1t Is possible that
future investigation may change the
situation In this respect In the pres.
ent state OF road science. however. IL
seems that where traffic conditions are
such that bituminous surface on n con.
crete rad Is practicable a bituminous
surface macadam road would be- equal.
ly practicable and certainly cheaper.
Where traffic Is too heavy for macndam
road the bituminous surface il likely
TO give way and the uneven manner IA
which II fails tends TO produce exces-
s!ve wear on portions OF the concrete.
For sucessful concrete road. hard
ness, toughDess and uniformity nre the
most essential qualities. These can lie
tn l., L.. -
selection Of the constituent materials
and the proportions in'which they are
mixed. The cement, IL Is said. should
always conform TO some standard spec.
ifications for portland cement. such
ax those issued by the United States
bureau OF standards or the American
Society For Testing Materials The
sand should not contain more than 3
per cent Of foreign material. and and
with more coarse than fine grains Il to
be preferred. The coarse aggregate
inny consist Of either crushed stone or
gravel. In either ease II Is very dcsira-
BILE that the coarse aggregate b. wcil
graded IN size between proper limits.
The proportion OF cement 10 the and
ana coarsc aggregate combined should
not DE less than nbout one 10 Eve. and
the proportion Of sand TO coarse aggre-
gate not less than one and one half to
three. nor greater than two 10 three.
A useful formula when gravel T. used
as coarse aggregate In one part ~ ce-
ment TO one md onchnlf part. Of sand
90 three parts of gravel. when erush.
cd stone II used one and three quar-.
ter parts Of sand may be substituted
In place Of one and nchnlf parts
In addition 10 discussing the cngi.
ncering details of construction the bul.
lctin calls attention 10 the fact that
ordinarily from one. third to one half of
the total cost Of constructing con-
crete pavement Il for labor after the
materials nrc delivered.
The most economical method IL 10
hnve the work Of mixing and placing
the concrete ~ nearly continuous as
practicable The work should b. plan.
ned with primary view ~ kecping
the mixer going full time. The drain.
age structures. the grading ard the
sub grade should. therefore. bc com.
plctsd well In advance OF the mixer
and provision made for obtainin. all
OF The necessary matcrinis without de.
lay. A common error Il the failure 10
make ndegu1te provision for deliver.
Ing water ON the work and the nmount
which given stream II capable Of sun.