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'''Road construction''' is a branch of [[civil engineering]] that uses engineering techniques to design and maintain flexible (asphalt) and rigid (concrete) pavements.  This includes streets and highways and involves knowledge of [[soil]]s, [[hydraulics]], and material properties.  Pavement engineering involves both new construction and maintenance of existing pavements.  Maintenance often involves using engineering judgment to make maintenance repairs with the highest long-term benefit and lowest cost.  The [[Pavement Condition Index]] ([[PCI]]) is an example of an engineering approach applied to existing pavements.  Another example is the use of a [[falling weight deflectometer]] (FWD) to non-destructively test existing pavements.  Calculation of pavement layer strengths can be performed from the resulting deflection data.
'''Road construction''' is the act of '''designing''', '''building''' and '''maintaining''' [[pavement (material)|pavement]]s and upper layers of transportation routes. Road pavements can be made of unbound materials such as [[soil]] and [[gravel]], though commonly roads are surfaced with [[Asphalt (paving)|asphalt]] or [[concrete]].  


==Design==
==Design==


Road design consists of two important technical aspects:
Road design consists of three technical aspects:
*[[geometrical road design]]
*[[geometrical road design]]: design of the line management of the road, including environmental issues.
*[[structural road design]]  
*[[structural road design]]: design of the body of the road
Besides these two technical sides of the design, environmental issues, planning issues and juridical issues are important.   
*[[road safety]]: design of the safety features of and next to a road
 
Besides the technical sides of the design, planning and juridical issues must be considered.   


==Construction==
==Construction==


The construction of a road usually starts with the preparation of the construction area in order to build up the [[pavement (material)|pavement]]. Removal of earth and rock by digging or blasting, construction of [[embankment]]s, [[bridge]]s and [[tunnels]], and removal of vegetation are often needed.  A variety of [[heavy equipment|road building equipment]] is employed in road building.


Road construction requires the creation of a continuous right-of-way, overcoming geographic obstacles and having grades low enough to permit vehicle or foot travel. Removal of earth and rock by digging or blasting, construction of [[embankment]]s, [[bridge]]s and [[tunnels]], and removal of vegetation (this may involve [[deforestation]]) are often needed.  A variety of [[heavy equipment|road building equipment]] is employed in road building.
Once these activities are completed, the construction of the '''road bed''' begins by [[compaction]] of the native [[soil]], known as the [[subgrade]]. Weak soils may be stabilized with additives such as [[portland cement]] or [[quicklime]], the use of [[geotextile]]s, or dug out and replaced with imported soils.
 
Once these activities are completed, construction of the [[pavement (material)|pavement]] can begin.  First the native [[soil]], known as the [[subgrade]], is [[compaction|compacted]]. Weak soils may also be stabilized with additives such as [[portland cement]] and [[quicklime]], or dug out and replaced with imported soils.
 
Then a [[base course]] consisting of [[gravel]] or crushed stone is usually placed on the subgrade and compacted.  On top of the base course is placed a surface course which typically consists of [[asphalt concrete]] or [[portland  cement concrete]].  This surface course strengthens the pavement structure by spreading out the vehicle loads applied to the subgrade.  It also provides a smooth and high-friction surface for vehicles to drive on. 
 
Modern roads, and indeed many ancient ones, such as those built by the [[Ancient Rome|Romans]], feature a convex transverse profile known as superelevation or [[camber]]. This is designed to allow water to drain away from the road to its edges. Water is then carried away by [[gutter]]s to [[drain]]s placed at intervals. Some roads don't have gutters and water simply drains away to a naturally porous verge, or into [[ditch]]es. Modern roads that carry motor traffic also employ camber in curves to aid traffic stability by allowing them to "bank into" the bend to some extent.
 
On the side of the road there may be [[retroreflector]]s on pegs, rocks or crash barriers, white toward the direction of the traffic on that side of the road, and red toward the other direction. In the road surface there may be [[Cat's eye (road)|cat's eye]]s: retroreflectors that protrude slightly, but which can be driven over without damage.  


[[traffic sign|Road sign]]s are often also made [[retroreflector|retroreflective]] or even illuminated in rare circumstances. For greater visibility of road signs at daytime, sometimes fluorescence is applied to get very bright colors.
Once the subgrade is prepared, a [[base course]] consisting of [[gravel]] or crushed stone is usually placed on the subgrade and compacted. High-traffic-volume roads will often have multiple layers of base courses, to reduce expense or increase performance. Depending on the road type, different kinds of layers are build on top of the [[base course]], e.g. [[Asphalt (paving)|asphalt concrete]] or [[portland cement concrete]]. Unbound materials such as [[soil]] or [[gravel]] are put on low-stressed roads such as farm tracks and country lanes. Roads made of asphalt or [[concrete]] provide a smooth and high-friction surface and  strengthen the pavement structure by spreading out the vehicle loads applied to the subgrade and are therefore used for high-stressed roads.  


==Maintenance==
==Maintenance==


Like all structures, roads deteriorate over time. Deterioration is primarily due to accumulated damage from vehicles, however environmental effects such as [[frost heave]]s, thermal cracking and oxidation often contribute.  According to a series of experiments carried out in the late [[1950s]], called the [[AASHO Road Test]], it was empirically determined that the effective damage done to the road is roughly proportional to the 4th power of [[axle]] weight. A typical tractor-trailer weighing 80,000 pounds with 8,000 pounds on the steer axle and 36,000 pounds on both of the tandem axle groups is expected to do 7,800 times more damage than a passenger vehicle with 2,000 pounds on each axle.  In most pavement design methodologies trucks are considered to be the sole cause of pavement deterioration.
Like all structures, roads wear out over time. This effect is primarily due to accumulated damage from vehicles, however environmental effects such as [[frost heave]]s, thermal cracking and oxidation often contribute.  According to a series of experiments carried out in the late [[1950s]], called the [[AASHO Road Test]], it was empirically determined that the effective damage done to the road is roughly proportional to the 4th power of [[axle]] weight. Therefore, trucks are considered to be the main cause of pavement deterioration, as they have individual axle loading between 5 and 9 times that of most passenger cars.  
 
Pavements are designed for an expected service life.  Most European countries have strict standards for road construction that require that most roads should be able to go 30 years or longer between major resurfacings.  In the United States new pavements are typically designed for a service life of between 15 and 25 years, depending on the importance of the road.  Service life predictions are inherently unreliable due to the difficulty of predicting future traffic and environmental conditions.
 
Virtually all roads require some form of maintenance before they come to the end of their service life.  Maintenance activities can be divided into structural maintenance and functional maintenance, although there is a great deal of overlap.  Structural maintenance is maintenance intended to preserve the structural integrity of the pavement, and includes patching [[pothole]]s, sealing cracks and overlays.  Functional maintenance is maintenance to improve the roadway's function of providing a smooth and safe surface for vehicles to drive on, and includes surface grinding and thin overlays.
 


[[Category:Engineering]]
Maintenance of a road can be divided in several types, from fixing small failures to a complete reconstruction of the road. Usually, [[heavy equipment|road building equipment]] is used to replace the top material layers and to rebuild them.
[[Category:Civil engineering]]
[[Category:Professions|Engineer, Pavement]]
[[Category:Architecture and engineering occupations]]
[[Category:Engineering_Workgroup]]

Revision as of 23:43, 5 February 2009

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Road construction is the act of designing, building and maintaining pavements and upper layers of transportation routes. Road pavements can be made of unbound materials such as soil and gravel, though commonly roads are surfaced with asphalt or concrete.

Design

Road design consists of three technical aspects:

Besides the technical sides of the design, planning and juridical issues must be considered.

Construction

The construction of a road usually starts with the preparation of the construction area in order to build up the pavement. Removal of earth and rock by digging or blasting, construction of embankments, bridges and tunnels, and removal of vegetation are often needed. A variety of road building equipment is employed in road building.

Once these activities are completed, the construction of the road bed begins by compaction of the native soil, known as the subgrade. Weak soils may be stabilized with additives such as portland cement or quicklime, the use of geotextiles, or dug out and replaced with imported soils.

Once the subgrade is prepared, a base course consisting of gravel or crushed stone is usually placed on the subgrade and compacted. High-traffic-volume roads will often have multiple layers of base courses, to reduce expense or increase performance. Depending on the road type, different kinds of layers are build on top of the base course, e.g. asphalt concrete or portland cement concrete. Unbound materials such as soil or gravel are put on low-stressed roads such as farm tracks and country lanes. Roads made of asphalt or concrete provide a smooth and high-friction surface and strengthen the pavement structure by spreading out the vehicle loads applied to the subgrade and are therefore used for high-stressed roads.

Maintenance

Like all structures, roads wear out over time. This effect is primarily due to accumulated damage from vehicles, however environmental effects such as frost heaves, thermal cracking and oxidation often contribute. According to a series of experiments carried out in the late 1950s, called the AASHO Road Test, it was empirically determined that the effective damage done to the road is roughly proportional to the 4th power of axle weight. Therefore, trucks are considered to be the main cause of pavement deterioration, as they have individual axle loading between 5 and 9 times that of most passenger cars.

Maintenance of a road can be divided in several types, from fixing small failures to a complete reconstruction of the road. Usually, road building equipment is used to replace the top material layers and to rebuild them.

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