Ashland tidings. [volume] (Ashland, Or.) 1876-1919, 1915-09-09
Concrete Roads
Are Popular

the Department OF Agriculture is OF
interest
"The mileage of concrete pave
ments in the United States has in
creased rapidly, and it is likely to
continue to increase, according to a
new bulletin of the department. This
bulletin gives the estimated amount
of concrete pavement in the United
States in 1914 as 100000 square
yards; in 1909 it was only 364, 900
square yards.
The principal advantages of con-
crete pavement which have led to
this increase in popularity are said
to be:
l. Durability under ordinary traf-
fic conditions,
2. A smooth, even surface offer
ing little resistance.
3. Absence of dust and ease with
which it may be cleaned.
4. Comparatively small cost Of
maintenance until renewals are nee
essary.
5. Availability as a base for an
other type of surface if desirable.
G. Attractive appearance.
In commenting upon these advan-
tages the bulletin states that the dur
ability of concrete roads has not yet
been proved by actual practice, be-
cause there are no very old pave
ments as yet in existence, but from
the condition of those which have
undergone several years service it
seems probable that they will be
found to wear well.
The disadvantages of concrete as
road surface are:
/. Its noise under horse traffic.
2. The wearing of the necessary
joints in the pavement, and the ten
dency to crack, with its consequent
rapid deterioration.
3. 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 a bitum-
inous wearing surface. At the pres
ent time, the specialists in the de-
partment hold that this can not be
economically justified, although it is
possible that future investigation
may change the situation in this re-
spect. In the present state of road
science, however, it seems that where
traffic conditions are such that BIZ
luminous surface on concrete road
is practicable a bitumlnous. surface
macadam road would be equally prac-
ticable and certainly cheaper. Where
traffic is too heavy for macadam
road the bituminous surface is likely
y give way and the uneven manner
in which it fails tends to produce ex-
cessive wear on portions of the con-
crete.
For a successful concrete road,
hardness, toughness and uniformity
are the most essential qualities.
These can be secured to a great eX-
tent by care in the selection of the
constituent materials and the pro-
portions in which they are mixed.
Sample specifications are included in
the bulletin, No. 249 Portland Gem
ent Concrete Pavements for Country
Roads. These specifications are be-
lieved to typily the best engineering
practice as it has been developed up
to this time. They cover such points
as materials, grading, subgrade and
construction.
The cement, It is said, should al
ways conform to some standard spec
ifications for Portland cement, such
as those issued by the United States
Bureau of Standards or the Ameri-
can Society for Testing Materials.
The sand should not contain more
than 3 per cent of foreign material,
and sand with more coarse than fine
grains is to be preferred. The
coarse aggregate may consist Of eth
er crushed stone or gravel In either
case it is very desirable that the
coarse aggregate be well graded in
size between proper limits.
The proportion of cement to the
sand and coarse aggregate combined
should not be less than about 1 to
s, and the proportion of sand to
coarse aggregate not less than V to
3, nor greater than to 8. A useful
formula when gravel is used as.
coarse aggregate is part of cement
to 1 Y parts of sand to parts of
gravel. When crushed stone is used,
1% parts OF sand may be substituted
in place OF Y parts.
In addition to discussing the en-
gineering details of construction, the