high molecular weight hydrocarbons, or which
asphalts, tars, pitches, and asphaltites are typical.
BLASTING MAT A heavy, flexible fabric of woven
wire rope or chain, used to confine blasts.
BLEEDING OR FLUSHING Is the upward
movement of asphalt in an asphalt pavement,
resulting in the formation of a film of asphalt on the
surface. The most common cause is too much
asphalt in one or more of the pavement courses,
resulting from too rich a plant mix, an improperly
constructed seal coat, too heavy a prime or tack coat,
or solvent-carrying asphalt to the surface. Bleeding
or flushing usually occurs in hot weather.
BLUE TOPS Grade stakes with blue tops to indicate
finish grade level, usually a 2-inch by 2-inch by
6-inch hub stake.
BM Bench mark.
BODY The load carrying part of a truck or scraper.
BOGIE AXLE Two or more axles, mounted to a frame
so as to distribute the load between the axles and
permit vertical oscillation of the axles.
BOOM CHORD A main corner member of a lattice
type of boom.
BOOM, CRANE A long, light boom, usually of lattice
BOOM HOIST Mechanism to control the elevation of
the boom and to support it.
BOOM LACING Structural truss members at angles
to and supporting the boom chords of a lattice type
BOOM, LATTICE A long, light boom fabricated of
crisscrossed steel or aluminum angles or tubing.
BOOM LENGTH Boom length is a straight line
through the center line of the boom pivot pinto the
center line of the boom point load hoist sheave pin,
measured along the longitudinal axis of the boom.
BOWL (1) The bucket or body of a carrying scraper.
(2) Sometimes the moldboard or blade of a dozer.
BUCKET A part of an excavator that digs, lifts, and
BULLDOZER (1) A tractor equipped with a front
pusher blade. (2) In a machine shop, a horizontal
CAPILLARY ATTRACTION The tendency of water
to move into fine spaces, as between soil particles,
regardless of gravity.
CASING A pipe lining for a drilled hole.
CAT (1) A trademark designation for any machine
made by the Caterpillar Tractor Company. (2)
Widely used to indicate a crawler tractor of any
CAT HEAD A capstan winch.
CATWALK A pathway, usually of wood or metal, that
gives access to parts of large machines.
CENTRIFUGAL FORCE Outward force exerted by
a body moving in a curved line. It is the force that
tends to tip a car over in going around a curve.
C-FRAME An angling dozer lift and push frame.
CHECK VALVE Any device that will allow fluid or
air to pass through it in only one direction.
CHOKER A chain or cable so fastened that it tightens
on its load as it is pulled.
CIRCLE REVERSE The mechanism that changes the
angle of a grader blade.
CLAM A clamshell bucket.
CLAMSHELL (1) A shovel bucket with two jaws that
clamp together by their own weight when it is lifted
by the closing line. (2) A crane equipped with a
CLAMSHELL BUCKET Usually consists of two or
more similar scoops hinged together and a head
assembly connected to the outer corners by struts.
When the head and hinge are pulled toward each
other, the scoops are forced together to dig and hold
material. Control is by a holding line reeved over a
boom point sheave and attached to the head
assembly to support the bucket in open position and
usually by a closing line also reeved over a boom
point sheave, ending in a force amplifying tackle or
other means between the head assembly and scoop
hinge to close the bucket.
CLAMSHELL BUCKET, HYDRAULIC Usually
consists of two or more scoops hinged to a head
assembly housing the hydraulic cylinder or
cylinders and the force amplifying linkage to open
and close the scoops and to supply the digging force
for the scoops. The bucket assembly is suspended
from the boom by a rope. Because digging ability is
largely dependent upon bucket weight, buckets are
supplied in various weight classes which range from