Montpelier examiner. [volume] (Montpelier, Idaho) 1895-1937, 1915-10-15

prepared by the United States Depart |
ment of Agricultural
Concrete roads have shown a |
marked increase in popularity during |
the past five years, according to the |
bodybuilding specialists of the U. S.
department of agriculture. In 1909
there were 364,000 square yards of
such roads in the United States, while
for 1914. the amount is estimated as
I 100000 square yards.
The durability of concrete roads has
not been proved by actual practice be-
cause there are no very old pavements
as yet in existence but from the condi-
ton of those which have undergone
several years service, it seems prob
able that they will be found to wear
we'll
The principal advantages of con-
crete pavements which have led to
their increased popularity are:
Durability under ordinary traffic
conditions.
A smooth, even surface offering lit
tie resistance.
Absence OF dust and ease with
which it may be cleaned.
Comparatively small cost of main
tenance until renewals are necessary.
Availability as a base for another
type of surface If desirable.
Attractive appearance.
On the other hand, concrete as a
road surface is noisy under horse
traffic, and has a tendency to crack
Unless these cracks are cared for at
once, they lead to rapid deterioration
of the adjacent pavement and finally
require difficult repair work.
In the past efforts have frequently
been made to overcome these objec-
lions to a certain degree by covering
the concrete pavement with bitumi
nous wearing surface. At the pres
ent time, the specialists in the de-
ment of agriculture hold that this
cannot be economically justified, al.
though it is possible that future inves-
tigation may change the situation in
this respect. In the present state of
road science, however. it seems that
where traffic conditions are such that
q bituminous surface on a concrete
road is practicable, bituminous sur
face macadam road would be equally
practicable and certainly cheaper.
Where traffic which is too heavy for
macadam road uses a bituminous con-
crete road, the bituminous surface is
likely to give way and the uneven
manner in which 1t fails tends to pro.
duce excessive wear on portions of
the concrete. For a successful con-
crete road, hardness, toughness, and
uniformity are the most essential quail
ho n -
great extent by care in the selection
of the constituent materials and the
proportions in which they are mixed.
Sample specifications are included in
the bulletin, No. 249, Portland Ce.
ment Pavements for Country Roads
These specifications are believed to
typify the best engineering practice
as 1t has been developed up to this
time. They cover such points as ma.
terials, grading. subgrade and con
struction.
The cement, it is said, should always
conform to some standard specifica
tions for Portland cement, such as
those issued by the United States
Bureau of Standards or the American
Society for Testing Materials. The
per cent of foreign material. and
sand with more coarse than fine grains
is to be preferred. The coarse aggre
gate may consist of either crushed
stone or gravel. In either case If /.
very desirable that the coarse aggre
gate be well graded in size between
proper limits
The proportion of cement to thu
sand and coarse aggregate combines
should not be less than about / to
and the proportion of sand to coars,
aggregate not less than " to 3. NO
greater than to 3. useful for
mula when gravel is used as coars
aggregate is l part Of cement to IL
parts of sand to 3 parts Of gravel
When crushed stone is used. q part
of sand may be substituted in place o
Ia parts
Ordinarily from l-5 to " Of tn