Comparison of Flexible and Rigid Pavement

Flexible Pavements	Rigid Pavements
- Deformation in the subgrade is transferred to the upper layers	- Deformation in the subgrade is not transferred to subsequent layers
- Have low completion cost but repairing cost is high	- Have low repairing cost but completion cost is high
- Have low life span	- High life span
- Surfacing cannot be laid directly on the subgrade but a subbase is needed	- Surfacing can be directly laid on the subgrade
- Road can be used for traffic within 24 hours	- Road cannot be used until 14 days of curing
- Have low flexural strength	- Have high flexural strength
- Damaged by oils and certain chemicals	- No Damage by oils

Asphalt

Asphalt (specifically, asphalt concrete) has been widely used since the 1920s. Most asphalt surfaces are laid on a gravel base, which is generally at least as thick as the asphalt layer, although some asphalt surfaces are laid directly on the native subgrade.

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Depending on the temperature at which it is applied, asphalt is categorized as hot mix, warm mix and cold mix. Cold mix asphalt is often used on lower volume rural roads, where hot mix asphalt would cool too much on the long trip from the asphalt plant to the construction site.

An asphalt concrete surface will generally be constructed for high volume primary highways having an average annual daily traffic load greater than 1200 vehicles per day. 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.

Concrete

http://www.concretepavements.org/Membership/Newsletter/ISCP_enewsletter_Vol1_No2.htm

Concrete surfaces (specifically, PCC) are usually used on roads with heavy traffic of heavy vehicles and 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. In many cases there will also be Portland cement substitutes added, such as fly ash. This can reduce the cost of the concrete and improve its physical properties.

Concrete surfaces are divided into three common types: jointed plain (JPCP), jointed reinforced (JRCP) and continuously reinforced (CRCP). Each of the jointing system types is used to control crack development.

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Jointed plain concrete pavement is the most common type of rigid pavement. JPCP controls cracks by dividing the pavement up into individual slabs separated by contraction joints. JPCP does not use any reinforcing steel but uses dowel bars and tie bars. Today the majority of US state agencies build jointed plain pavements.

Jointed reinforced concrete pavements control cracks by dividing the pavement up into individual slabs separated by contraction joints. However, these slabs are much longer than JPCP slabs, so JRCP uses reinforcing steel within each slab to control within-slab cracking. Today very few of agencies use this design, because it is not recommended as both of the other types offer better performance and are easier to repair.

Continuously reinforced concrete pavements use reinforcing steel rather than contraction joints for crack control. Cracks are held tightly together by the underlying reinforcing steel. A number of agencies have made decisions to use continuously reinforced designs in their heavy urban traffic corridors.

One of the major advantages of concrete pavements is that they are typically stronger and more durable than asphalt roadways. They can also provide a durable skid-resistant surface. A notable disadvantage is that it can typically have a higher initial cost, as well as can be more time consuming to construct. This cost can typically be offset through the long life cycle of the pavement.

Other pavements

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

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Bituminous surface treatment (BST) 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. The aggregate is then embedded into the asphalt by rolling it, typically with a rubber-tired roller. This type of surface is described by a wide variety of regional terms including "chip seal", "oil and stone" etc.

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.

http://commons.wikimedia.org/wiki/File:Gravel_Road_Coober_Pedy.jpg

Gravel is known to have been used extensively in the construction of roads by soldiers of the Roman Empire. A granular surface can be used with a traffic volume where the average annual daily traffic is 1,200 vehicles per day or less. There is some structural strength as the road surface combines a sub base and base and is topped with a seal aggregate with emulsion. The decision whether to pave a gravel road or not often depends on traffic volume. Obviously, it is not as durable as concrete or asphalt pavements, but relatively cheap.

Pavers generally have the form of pre-cast concrete blocks, are often used for aesthetic purposes. Pavers are rarely used in areas with high-speed vehicle traffic.

en.wikipedia.org/wiki/Road_surface

Brick, cobblestone, sett pavements were once common in urban areas throughout the world, but fell out of fashion in most countries, due to the high cost of labor required to lay and maintain them, and are typically only kept for historical or aesthetic reasons. In some countries, however, they are still common in local streets.

Step I: Planning

A road project begins with evaluating the transportation system, taking into account statewide priorities, including strategic plans for the state’s transportation system. Department of Transportation collects and maintains information about our roads, including road and bridge conditions, traffic volumes, crash statistics.

Using this data, transportation planners, engineers, environmentalists, landscape architects, soil scientists and others identify trends that determine what and how to build.

http://www.michigan.gov/mdot/0,1607,7-151-9615-129011--,00.html

Step II. Design

A survey of the area is step two. Recently, Global Positioning Systems, laser surveys, and other technology have sped up the process and improved accuracy. Many factors influence designs, including location, terrain and soil properties, drainage capabilities, traffic volume, the ratio of cars to trucks and buses, possible future development in the area, effects on the environment or nearby residents.

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