The Belding banner-news. (Belding, Mich.) 1918-1973, 1918-10-02
Concrete Road Construction.
BY VIM. w Cox. Deputy State High
way missioner.

lAA way Commissioner.
The construction Of concrete road
appears very simple to the average
person who has not made thorough
study and investigation into the es-
sential detail entering in the the OPP
Grafton from start to finish. Ade-
quate drainage, preparation OF SUBJ
grade, selection of materials, work
manship and protection, all have an
important bearing upon the desired
results of obtaining a first class con-
crete road.
The all too common practice of
Fplacing concrete on a poorly drained
grade cannot be condemned too
strongly. Simply because of the
bearing power or rightly of concrete
many are inclined to think that the
presence of water in the subgrade
does no particular harm. A con-
crete road so placed may show up
very well for a short time, but sooner
or later the action of frost and the
result of heavy loaded vehicles will
cause the concrete TO crack badly and
thus eventually result in complete
failure of the road. 1t is therefore
necessary to first provide good drain
age so that the water level in the
subgrade is at least two feet below
the concrete. 1t has been observed
that where concrete roads have been
built on new rights of way where the
entire grade was made new, that very
seldom any longitudinal cracks devel
OPP. Also longitudinal cracks in cuts
approximately as follows:
Per cent
Passing in. screen -. -. 100
Retained on a l in. screen not
Passing inch screen not less
Retained on a Ia n. screen not :.
If it is found impractical to obtain
such grading of gravel, and another
grading is used, it should be an even
grade in respect to keeping the voids
constant.
Crushed stone should be good angu-
lar fracture, even run in hardness and
when tested by standard method, it
should show toughness of at least
eight and a French coefficient of wear
of not less than ten. Some of our
/ limestone deposits. if handled with
care, can be used for coarse aggre-
gate. Crushed cobbles or field stone
when properly sorted. can in many
localities be used to distinct advan-
tage.
> In the selection Of both crushed
stone and gravel, coated or dirty ma
terial should be rejected, even though
the percentage of clay or silt is COM
paratively small. The range in size,
even run and per cent of voids for
crushed stone, should be about the
same as for gravel.
Fine aggregate should be practical
1y clean of silt, clay or loan and
graded approximately as follows:
Passing Ia in. screen -. -. 100
Retained on No. 20 sieve, not more
Retained on No. 20 sieve, not less
Passing No. SO sieve not more than. 20
A coarser sand is recommended
when used with crushed stone. Ce-
'ment should meet the requirements
of the American Society for Testing
Materials in 1916.
7 Water should be free from oil, acid :.
'alkih, vegetable mater and fairly free
from clay or silt. The forms should
have straight surface and should be
set in true grade and so thoroughly
staked that no movement can take
place when concreting and finishing
is being done. The batch mixer is
considered the standard and should
be so equipped that the number Of
revolutions for given length Of time
can be easily obtained.
The amount Of labor used in the
laying Of concrete should be such
that every detailed operation can be
completed ct the proper time and 80
that the whole 10 steady progress
sion. The more nearly the proper
ti0ns OF coarse and fine aggregates
the proportion of cement and the con-
sistency Of the batche. can be made
uniform, the most certain that the con
crete when seasoned will give an even
resistance to wear. The amount of
water used in the mix should be just
enough to insure that the mixer will
completely discharge its batch to the
conveyor. Alternate dry and very
wet patches will cause unequal shrink
age in the body of the concrete and
hence a wavy and unsatisfactory sur
face by the use Of too much water
than in any other way. @
The subgrade should be well satur-
'ated before placement of concrete so
as to avoid losing too much moisture
before the finishing is complete.
The finishing of the concrete after
being shoveled in place, should pro-
ceed Immediately. It should be sur
face struck by rigid template few
times over and then allowed to set
Few minutes until the surplus water
comes to the top. The use of the
roller Of the Macon type has proved
great help in the finishing of the sur
face. Another great advantage in
using the roller is that the ridges and
depressions made by the striking tenn
plate are entirely removed by rolling
a few times over. 1t should be OPP
Grated, however, with care and judg-
ment so as not to roll out the crown
or make heavy depressions next to
the forms. The rollers which seem
to be the most satisfactory are about
10 inches in diameter, feet long and
weigh about rs pounds.
Cracks and joints are admitted to
be the weak points of well con-
styucted concrete road, hence great