VII Международная студенческая научная конференция Студенческий научный форум - 2015

Pavement Types

Road surface or pavement is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past, gravel road surfaces, cobblestone and granite setts were extensively used, but these surfaces have mostly been replaced by asphalt or concrete laid on a compacted base course. Road surfaces are frequently marked to guide traffic.

Asphalt (specifically, asphalt concrete) has been widely used since the 1920s. The viscous nature of the bitumen binder allows asphalt concrete to sustain significant plastic deformation, although fatigue from repeated loading over time is the most common failure mechanism. Most asphalt surfaces are laid on a gravel base, which is generally at least as thick as the asphalt layer, although some 'full depth' asphalt surfaces are laid directly on the native subgrade.

In areas with very soft or expansive subgrades such as clay or peat, thick gravel bases or stabilization of the subgrade with Portland cement or lime may be required.

Advantages of asphalt roadways include relatively low noise, relatively low cost compared with other paving methods, and perceived ease of repair.

Disadvantages include less durability than other paving methods, less tensile strength than concrete, the tendency to become slick and soft in hot weather and a certain amount of hydrocarbon pollution to soil and groundwater or waterways.

In the 1960, rubberized asphalt was used for the first time, mixing crumb rubber from used tires with asphalt.

While a potential use for tires that would otherwise fill landfills and present a fire hazard, rubberized asphalt has shown greater incidence of wear in freeze-thaw cycles in temperate zones due to non-homogeneous expansion and contraction with non-rubber components

Concrete surfaces

Concrete surfaces (specifically, Portland cement concrete) are created using a concrete mix of Portland cement, coarse aggregate, sand and water. In virtually all modern mixes there will also be various admixtures added to increase workability, reduce the required amount of water, mitigate harmful chemical reactions and for other beneficial purposes.

A concrete road in Ewing, New Jersey. The original pavement was laid in the 1950 and has not been significantly altered since.

Composite surfaces

An example of composite pavement: hot mix asphalt overlaid onto Portland cement concrete pavement

Composite surfaces combine Portland cement concrete and asphalt. They are usually used to rehabilitate existing roadways rather than in new construction.

Bituminous surface

Bituminous surface treatment (BST) or chip seal is used mainly on low-traffic roads, but also as a sealing coat to rejuvenate an asphalt concrete pavement. It generally consists of aggregate spread over a sprayed-on asphalt emulsion or cut-back asphalt cement.

BST is used on hundreds of miles of the Alaska Highway and other similar roadways in Alaska, the Yukon Territory, and northern British Columbia. The ease of application of BST is one reason for its popularity, but another is its flexibility, which is important when roadways are laid down over unstable terrain that thaws and softens in the spring.

A thin membrane surface (TMS) is an oil treated aggregate which is laid down upon a gravel road bed producing a dust free road.[15] A TMS road reduces mud problems and provides stone free roads for local residents where loaded truck traffic is negligible. The TMS layer adds no significant structural strength, and so is used on secondary highways with low traffic volume and minimal weight loading.

Origin

Internet:

http://en.wikipedia.org/wiki/Road_surface

http://en.wikipedia.org/wiki/Gravel_road

http://onlinemanuals.txdot.gov/txdotmanuals

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