The Jasper news. [volume] (Jasper, Missouri) 1898-1924, 1917-09-13

3. In direct proportion to the value
as q cementing material under all con-
ditions of weather. Of the finer par
ticles of earthly matter constituting
the filler or binder.
In general, the physical characters
tics of gravel which determine its
suitability for use in surfacing road
| are:
l. ~ The durability of the pebbles or
rock fragments, (2) the quality Of the
binder, (3) the grading of the pebbles,
and (4) the proportion in which the
binder material Is present While the
influence each Of these factors should
exert in fixing the selection Of gravel
| for particular road depends upon To-
cal conditions and necessarily is a
question for individual judgment to
decide, nevertheless n few points in
connection with each factor that may
aid materially In reaching q decision
will be summarized in the following
paragraphs.
Durability Of Pebbles.
The principal qualities which deter
| mine the durability of pebbles or
stone Of any kind when placed In Il
road surface are hardness, toughness,
and resistance to wear. The extent
to which pebbles possess these quail
ties depends very largely on the char
acter Of the parent stone from which
they were originally produced and ac-
cordlngly varies over wide range.
Since nearly all gravel deposits con-
| tain pebbles which have been formed
from many different kinds Of stone,
1t has not been considered practicable
to apply the ordinary laboratory tests
for determining hardness, toughness,
and per cent of wear to gravel, and
the matter of comparing these quail
| ties, as possessed by the pebbles from
different gravel deposits, usually de-
pends on visual inspection. Not infre-
Quently very casual inspection will
reveal which deposit, among great
number, contains the largest percen-
tage Of hard, durable pebbles. There
are comparatively few cases where
this point cannot be determined with
sufficient accuracy by sorting out the
pebbles contained in representative
samples from the different deposits,
testing the various kinds with hand
hammer, and determining the relative
proportions in which the more durable
materials are present in the sample by
means OF. weighing device.
| The Binder.
No matter how durable may be the
pebbles contained in a given gravel
deposit, they cannot be used success
fully in road surface unless they can
be well bonded together so as to pre-
sent q combined resistance to the dis
turbing action Of traffic. To accom-
plish this bond requires that the gravel
contain some cementing or binding
agent such rs iron oxide, carbonate
Of lime, or clay. AS already explained,
certain pebbles, such as those COM
posed Of limestone, possess the prop
erty Of becoming firmly bonded togeth-
er by virtue of their own cementing
value.
Grading and Proportions.
For gravel to make a satisfactory
road surface, the stone particles
should be graded in size so that the
amount of binder required will be
reduced to a minimum. The reason
for this Is that the binder usually Is
much less resistant to wear than the
stone particles, and therefore it is de
sirable that the latter form as large
part of the wearing surface as Is
practicable. Most gravel deposits n.
they occur In nature satisfy this re
quirement in so far as grading of tht
pebbles Is concerned, but they nearl!
always contain pebbles Of size larg
er than 1t Is desirable to incorporate
In a road surface. Natural deposit
/ also not infrequently contain too larg
n proportion of sand or clay to pro
duce satisfactory results. 1t is desira
, BILE, therefore, that specifications GOV
: ering gravel for use in road construc
tion should limit the proportions Ii
= which the fine and coarse material
2 shall be present and a maximum limit
ing size for the pebbles, as well n
3 definite requirements regarding tn
) quality of the pebbles and Of tn
binder.