Oxford Democrat. [volume] (Paris, Me.) 1833-1933, 1897-07-20
CLAY AS ROAD METAL
NOT DESIRABLE EXCEPT IN SMALL
QUANTITIES.

QUANTITIES.
Acts n . Cement to Knit the Stone To-
gether when Properly used-Action Of
Water ON the Raadbed - Prevents Dast
and wear-Trees and Hedges.
The part played by water o. crushed
stone while undergoing rolling Is sew
eral fold. In practice broken stone CON-
pletely wet down isthoroughly rolled
with q roller weighing ten or more
tons. The wet surface Of the angular
rock fragments permits more thorough
compacting as the water acts a. lu-
bricant. allowing the stones to slip by
one another with greater freedom than
would be the case were the fragments
dry. At tie same time the water re-
tains the powdered rock resulting from
abrasion Of the particles and holds it
between the fragments.
This process is reactionary and cumu-
lative, for the presence Of the powder
| Of nttrition acts through capillarity TO
take up aIsi retain still greater guam.
titles Of water until the spaces between
the pieces Of broken stone composing
the upper Part Ct the road become COM
pletely filed with powdered rock. Net
| q little Of the ctmontine or bonding Of
u road during rolling is in reality tie
effect of capiilarity existing between the
| grains Of powdered rock and the al.
| joining walls.
This principle may be observed Oh
our seashoros and sand reads. While
wet, the beach or road may be firm and
unyieldiDg, allowing heavily loaded
teams to pass over them, but when dry
such places are imrassatlc for heavy
teams and difficult Of passage for all
kinds Of vehicles. In this case cement
ing, as ordinarily understood, plays 70
part in producing adhesion between
the grains Upon drying, the grains cGe
| entirely free 10 move over Cne another,
| having lost the water which served 20
bind them together
When u mac adam road is thoroughly
eompacted, careful inspection Will
show that the fragments of broken stone
are closely packed together aud the
spaces between are filed with fine
powdered rcck, which. If derived from
| q suitable ,oad material. carries small
percentage Of clay. Any OF cur COM
| monty used read stones contains an ap-
preciable quantity Of clay disseminated
| in little articles III the teldspar whence
| il has been derived by the weathering
| Of the rock prior 10 Its removal from
the quarry.
The microscope shows that the field
spar Of our traps and GRANTEES and otl r
road stones is never entirely free from
a considerable amount of kaolinizat!on
or alteration to clay. This change has
taken place III tie crust Of the earth 10
q great depth. and no road material can
contain feldspais free from more or less
of this mineral, depending upon the
character Of tie iCck and the amount
Of weatbering 10 (Which it has been sub
iected. BY the gradual wearing Of the
feldspar. by the abrasive action Of the
roller, the heels of carriages, and the
| feet Of animals, "a small but important
quantity Of clay is liberated, and this
| in combination with any clayey ma
| terial that may have been added to the
road serves To furnish the necessary
quantity Of cement 10 kit the broken
stone firmly together. 1t is not 10 be
understood that III appreciable quantity
| Of clay acts otherwise than objection
ably when used in roadbuildipg. AS Il
rule nothing u r.Cie Undesirable ilan
the clay element in highway construc'
tion, yet little mixed with some CT
Our southern limestcnes serves 10 IN
crease their cemeutiug and enduring
qualities. Upon drying, the powdered
rock sets much after the manner of a
sandy clay and serves not only to bind
the pieces Of rcck together, thus giving
rigidity to the way, but to retaId the
wear due to ally differential motion OF
the fragments over one another while
the lead is passing along the road. A
wetting Of the superficial PORTION Of a
roadway during rains tends by the ex-
pansion Of the cement TO knit tue sur
face together and make il impermeable
to the passage Of water.
From theoretical standpoint 1t
would seem probable that'a certain con-
dition Of moisture instead Of being OBJ
jecticnable to roadway undergoing
constant use is rather d, ,sirable than
otherwise. A condition Of moistness
serves 10 prevent loss Of material worn
fine by the abrasive action Of the wind,
and the presence Of thin film Of wet
dust acts as II cushion to protect the
fragments OF rock from the rude touch
and impact Of passing traffic, thus less
enipg the wear aud tear Of the surface.
In the same manner the moist cement
operates to distribute the bearing sur
faces Of the broken stone and 10 reduce
the local intensity Of the friction be-
tween one rock and another, although
cement in this condition will tend to
allow greater freedom Of movement
among the broken stones, and hence IN
this way make the surface more yield
ing Assuming llat the loss through
increased abrasion If material resulting
from moist cement between the rock
fragments is equal to the saving due to
the cushioning effect Of u small quanti-
" of moisture Oh tie surface, there still
remains saving to the road by the
protection afforded by preventing ex.
cessive loss through the action Of the
wind.
1t is the custom in England to plant
hedgerows beside macadamized roads
In order TO insure rapid drying Of the
road after rain by the suns action.
In Germany it has been the practice to
plant fruit trees, particularly the cher.
~, while in France the mulberry tree
may be seen along the roadsides. serv-
ing the double purpose Of food for silk
worms and shade.
In this country no precedent has
been established in the matter. The
states in deciding this question must Of
course consider latitude and longitude
as affecting tie cbara, ter Of the trees
that will flourish therein and their re-
Ilation to climatic conditions. l.
Whittle.