The Abbeville press and banner. [volume] (Abbeville, S.C.) 1869-1924, 1900-01-17
CLAY AS ROAD METAL
MOT DESIRABLE EXCEPT IN SMALL
QUANTITIES.

Acts as . Cement to Knit tho Stone To-
eether When Properly Used-Action OF
Water on the Roadbed Prevents Dust
and Wear-Trees and Hedges. -
The part played by water on crushed
stone while undergoing rolling IS sew
eral fold. In practice broken stone com
pletely wet down is thoroughly rolled
with roller weighing ten or more
tons. The wet surface of the angular
rock fragments permits a more thorough
compacting, as the water acts as a lu-
bricant, allowing the stones to slip py
one another with greater freedom than
would be the case were the fragments
dry. At the same time the water re-
tains the powdered rock resulting 1rom
abrasion Of the particles and holds II
between the fragments. -
This process is reactionary and cumu-
lative, for the presence Of the powder
of attrition acts through capillarlty 10
take up and retain still greater guam
titles of water until the spaces between
the pieces of broken stone composing
the upper part of the road become COM
pletely filled with powdered rock. Not
a little of the cementing or bonding OF
q road during rolling is in reality the
effect of capillarity existing between the
grains OF powdered rock and the aG-
joining walls.
This principle may be observed on
| ,op1 rno1c Wh1la
wet, the beach or road may be firm and
unyielding, allowing heavily loaded
teams to pass over them, but when dry
such places are impossible for heavy
teams and difficult Of passage for all
kinds of vehicles. In this case cement
ing, as ordinarily understood, plays no
part in producing adhesion between
the grains. Upon drying, the grains are
entirely free to move over one another'
having lost the water which served 70
bind them together. -.
When a macadam road is thoroughly
compacted, careful inspection Will
show that the fragments Of broken stone
are closely packed together and the
spaces between are filled with a fine
powdered rock, which, if derived from
suitable road material, carries a1small
\ percentage of clay. Any OF our COM
mohlysused road stones contains an ap-
precikbie quantity of clay disseminated
in Ii6tie PARTICLES in the feldspar whence
4 II haSs been derived by the weathering
.of tts rock prior to its removal from
| TIA s21i7STrpss. -.
T6a microscope shows that the field
sparf Dur traps and GRANTEES and other
road is never entirely free from
a c6n6S5erabIe amount Of kaolinization
or al2 Hon to clay. This change has
takens 6iaceRin the crust Of the earth to
q great depth, and no road material can
contain Yeldspars free from more or less
of this mineral, depending upon the
characteHDf the rock and the amount
of weathering to which it has been SUBJ
i Elected. Blythe gradual wearing of the
Il ;feldspais fby the abrasive action OF the
s ErolleEi fhesWheels Of carriages, and the
Il Hfeetpf $nimals, small but important
4 df1aaititysof clay is liberated, and this
Iisin mbiaation with any clayey ma
vi that may have been added TO the
y sst|sslxSad serves to furnish the necessary
= ssGfhantitysnf cement to knit the broken
st0nB frnfly together. It is not to be
apnderatcod that an appreciable quantity
II 5j6e 1lay acta ctherwise than objection
q @ 1a When: :ussd in roadbuilding. Asa
5le thing sism more undesirable than
q c1ag element ip; highway consttss,yA
st Is tattSs III Il tile MIXED with SOM
A stsiF uGt hern Iimsstones serves to J
their estnenting and enduring,
Iauali till Upon drying, the powdered
& rock sets mnch after the manner Of a
H SE5sandy clay serves not only to bind
& pienes dt roSk together, thus giving
toths way; but to retard the
due o ANY differential motion Of
stfiE frS8 tents over one another while
the load lie passing along the road. A
. wetfingpf the superficial portion Of q
roadwaysduring rains tends by the ex-
4 pansion Of the cement to knit the sur
face together and make it impermeable
to thspassage Of water. -
FfomiA theoretical standpoint ii
would seem probable that certain con-
iEdition of moisture instead Of being OBJ
i jetionable to a roadway undergoing
3 constant use is rather desirable than,
4 ctherWiSe "a condition OF moistnesa
A serves to prevent loss of material worn
Lane by. the abrasive action Of the wind,
and the presence of thin film Of wet
A dust adts as a cushion to protect the
q fragments of rock from the rude touch
4 md impact Of passing traffic, thus less
sf9ning the wear and tear Of the surface.
In the same manner the moist cement
operates to distribute the bearing sur.
faces Of the broken stone and to reduce
the local intensity Of the friction be-
tween one rock and another, although
cement ID this condition will tend to
allow d greater freedom of movement
4 aamong the broken stones, and hence in
this way make the surface more yield
ing. Assuming that the loss through
increased abrasion of material resulting
from moist cement between the rock
fragments is equal to the saving due to
the cushioning effect of small quanti-
ty of moisture on the surface, there still
remains a 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