CHAPTER 6 TRANSPO

highway pavements

act as the essential foundation of roads

flexible pavements

designed to flex and adapt under load. consist of multiple layers, providing a smooth surface and allowing for greater distribution of stresses.

rigid pavements

made from portland cement concrete, act as beams. they rely on the thickness and material strength, falling primarily through fatigue cracking over time.

layered pavement system

effectively distributes load pressure, enhancing durability and performance while allowing for cost optimization by utilizing less dense material in lower layers.

equivalent single axle load

quantify road damage , emphasizing that a single heavy truck can cause damage equivalent to thousands of passenger cars

AASHTO method

utilizes the structural number formula to balance thickness of pavement layers and the strength of materials

California method

employs the Traffic index and R-values to determine the gravel equivalent thickness necessary for various traffic conditions

layer thickness

crucial in distributing loads effectively, allowing for cost-efficient designs while maintaining structural integrity and performance under varying conditions

material strength

selecting appropriate materials based on their strength is essential

drainage

removal of excess water in a surface or subsurface of a particular area

alligator cracking

appears as interconnected cracks resembling alligator's skin, caused by fatigue from heavy loads and repetitive stress on the asphalt surface over time

rutting

manifests as depression in the the wheel paths due to the permanent deformation of asphalt

bleeding

occurs when excess asphalt rises to the surface, creating a glossy appearance

alligator cracking

rutting

bleeding

common asphalt distresses 3

faulting

occurs at joints where vertical displacement happens, leading to uneven surface that can compromise ride quality and safety for vehicles traveling over the pavement

cracking

can manifest in various forms, typically stemming from temperature fluctuations, inadequate joint spacing, or heavy traffic loads

blow-ups

serious issue that occurs when heated concrete expands and cannot release pressure, resulting in buckling that can severely damage the pavement structure and disrupt traffic

spalling

characterized by chipping of slab edges, often caused by freeze-cycles or heavy loads

faulting

cracking

blow-up

spalling

common concrete distresses 4

rail

guide and support trains, ensuring they remain on track

fastener

secure rails to railroad ties, maintaining gauge, stability, and proper alignment

ties/sleepers

crucial for holding the rails in place

ballast

consists of crushed stone placed beneath the tracks

subgrade

foundation layer of compacted natural soil or engineered material situated directly beneath the railway ballast and sub-ballast

rails

fasteners

ties/sleepers

ballast

subgrade

railroad track components 5

jointed track

traditional; uses joint bars to bolt rail segments together. The small gaps allow for thermal expansion but create a discontinuous surface

continuously welded rail

modern; modern rails are welded into seamless threads, minimizing impact points and reducing maintenance

turnouts/switches

consists of a pair of tapered point rails that can be moved back and forth

frogs

the v-shaped crossing point where two rails intersect

guard rail

consists of a pair of tapered point rails that can be moved back and forth g