light, for easily dug stockpiled materials, to heavy,
for excavating hardpan material and the like.
CLAMSHELL EQUIPMENT Machines with
clamshell attachments are used to load material
from stockpiles, gondola cars, barges, and the like,
or from virgin soil generally out of small-area holes,
deep trenches, or from below water. Orange peel
buckets, grapples, and similar rope suspended
attachments are included in this classification.
CLOSING LINE The rope reeved from the hoist drum
to control closing of a rope-operated clamshell
COFFERDAM A set of temporary walls, designed to
keep soil and/or water from entering an excavation.
COLLAR A sliding ring, mounted on a shaft so that it
does not revolve with it, used in clutches and
COMPACTION The act of compressing a given
volume. Insufficient compaction of the asphalt
pavement courses may result in channeling on the
pavement surface. Compaction is usually
accomplished by rolling.
CONVEYOR BELT An endless belt of rubber-
covered fabric that transports material on its upper
CORRUGATIONS (WASHBOARDING) AND
SHOVING Are types of pavement distortion.
Corrugation is a form of plastic movement typified
by ripples across the asphalt pavement surface.
Shoving is a form of plastic movement, resulting in
localized bulging of the pavement surface. These
distortions usually occur at points where traffic
starts and stops, on hills where vehicles brake on the
downgrade, on sharp curves, or where vehicles hit
a bump and bounce up and down. They occur in
asphalt layers that lack stability. Lack of stability
may be caused by a mixture that is too rich in
asphalt, has too high a proportion of fine aggregate,
has coarse or fine aggregate that is too round or too
smooth, or has asphalt cement that is too soft. It may
also be due to excessive moisture, contamination
due to oil spillage, or lack of aeration when placing
mixes using liquid asphalt.
CRACKS Breaks in the surface of an asphalt
CRACKS, ALLIGATOR Interconnected cracks
forming a series of small blocks resembling an
alligators skin or chicken wire, caused by excessive
deflection of the surface over unstable subgrade or
lower courses of the pavement.
CRACKS, EDGE JOINT Are the separation of the
joints between the pavement and the shoulder,
commonly caused by the alternate wetting and
drying beneath the shoulder surface. Other causes
are shoulder settlement, mix shrinkage, and trucks
straddling the joint.
CRACKS, LANE JOINT Longitudinal separation
along the seam between two paving lanes caused by
a weak scam between adjoining spreads in the
courses of the pavement.
CRACKS, REFLECTION Cracks in asphalt overlays
that reflect the crack pattern in the pavement
structure underneath. They are caused by vertical or
horizontal movements in the pavement beneath the
overlay, brought on by expansion and contraction
with temperature or moisture changes.
CRACKS, SHRINKAGE Are interconnected cracks
forming a series of large blocks, usually with sharp
corners or angles. Frequently they are caused by
volume change in either the asphalt mix or in the
base or subgrade.
CRACKS, SLIPPAGE Are crescent-shaped cracks
that are open in the direction of the thrust of wheels
on the pavement surface. They result when there is
a lack of good bond between the surface layer and
the course beneath.
CRANE A mobile machine, used for lifting and
moving loads without the use of a bucket.
CRANE MATS A device, used for supporting
machines on soft ground, usually of timber
CREEP (1) Very slow travel of a machine or a part. (2)
Unwanted turning of a shaft due to drag in a fluid
coupling or other disconnect device.
CRUMBER A blade that follows the wheel or ladder
of a ditching machine to clean and shape the bottom.
CULVERT A pipe or small bridge for drainage under
a road or structure.
CURVE, VERTICAL A change in gradient of the
center line of a road or pipe.
CUTBACK ASPHALTS Mixture of asphalt cement
and a cutting agent. There are three main types.
DATUM Any level surface taken as a plane of
reference from which to measure elevations.