light, for easily dug stockpiled materials, to heavy,for excavating hardpan material and the like.CLAMSHELL EQUIPMENT— Machines withclamshell attachments are used to load materialfrom stockpiles, gondola cars, barges, and the like,or from virgin soil generally out of small-area holes,deep trenches, or from below water. Orange peelbuckets, grapples, and similar rope suspendedattachments are included in this classification.CLOSING LINE— The rope reeved from the hoist drumto control closing of a rope-operated clamshellbucket.COFFERDAM— A set of temporary walls, designed tokeep soil and/or water from entering an excavation.COLLAR— A sliding ring, mounted on a shaft so that itdoes not revolve with it, used in clutches andtransmissions.COMPACTION— The act of compressing a givenvolume. Insufficient compaction of the asphaltpavement courses may result in channeling on thepavement surface. Compaction is usuallyaccomplished by rolling.CONVEYOR BELT— An endless belt of rubber-covered fabric that transports material on its uppersurface.CORRUGATIONS (WASHBOARDING) ANDSHOVING— Are types of pavement distortion.Corrugation is a form of plastic movement typifiedby ripples across the asphalt pavement surface.Shoving is a form of plastic movement, resulting inlocalized bulging of the pavement surface. Thesedistortions usually occur at points where trafficstarts and stops, on hills where vehicles brake on thedowngrade, on sharp curves, or where vehicles hita bump and bounce up and down. They occur inasphalt layers that lack stability. Lack of stabilitymay be caused by a mixture that is too rich inasphalt, has too high a proportion of fine aggregate,has coarse or fine aggregate that is too round or toosmooth, or has asphalt cement that is too soft. It mayalso be due to excessive moisture, contaminationdue to oil spillage, or lack of aeration when placingmixes using liquid asphalt.CRACKS— Breaks in the surface of an asphaltpavement.CRACKS, ALLIGATOR— Interconnected cracksforming a series of small blocks resembling analligator’s skin or chicken wire, caused by excessivedeflection of the surface over unstable subgrade orlower courses of the pavement.CRACKS, EDGE JOINT— Are the separation of thejoints between the pavement and the shoulder,commonly caused by the alternate wetting anddrying beneath the shoulder surface. Other causesare shoulder settlement, mix shrinkage, and trucksstraddling the joint.CRACKS, LANE JOINT— Longitudinal separationalong the seam between two paving lanes caused bya weak scam between adjoining spreads in thecourses of the pavement.CRACKS, REFLECTION— Cracks in asphalt overlaysthat reflect the crack pattern in the pavementstructure underneath. They are caused by vertical orhorizontal movements in the pavement beneath theoverlay, brought on by expansion and contractionwith temperature or moisture changes.CRACKS, SHRINKAGE— Are interconnected cracksforming a series of large blocks, usually with sharpcorners or angles. Frequently they are caused byvolume change in either the asphalt mix or in thebase or subgrade.CRACKS, SLIPPAGE— Are crescent-shaped cracksthat are open in the direction of the thrust of wheelson the pavement surface. They result when there isa lack of good bond between the surface layer andthe course beneath.CRANE— A mobile machine, used for lifting andmoving loads without the use of a bucket.CRANE MATS— A device, used for supportingmachines on soft ground, usually of timberconstruction.CREEP— (1) Very slow travel of a machine or a part. (2)Unwanted turning of a shaft due to drag in a fluidcoupling or other disconnect device.CRUMBER— A blade that follows the wheel or ladderof a ditching machine to clean and shape the bottom.CULVERT— A pipe or small bridge for drainage undera road or structure.CURVE, VERTICAL— A change in gradient of thecenter line of a road or pipe.CUTBACK ASPHALTS— Mixture of asphalt cementand a cutting agent. There are three main types.DATUM— Any level surface taken as a plane ofreference from which to measure elevations.AI-3
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