1 Introduction
1.1 History of roads and the need for assessment
2 Road types and profiles
2.1 Unpaved roads
2.2 Paved roads
3 Common road defects
3.1 Structural adequacy
3.2 Skid resistance
3.3 Surface defects
3.3.1 Unpaved roads
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Potholes: Bowl-shaped holes caused by the movement of loose surface material under traffic loads. They become problematic if their depth and diameter becomes greater than 25 mm and 200 mm, respectively.
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Rutting: Longitudinal deflections along the wheel-path caused by permanent deformation or compaction of road material under traffic loading. Unpaved roads constructed over a subgrade with a high clay content or with minimal surface coarse aggregate are prone to rutting in wet conditions.
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Corrugations: Evenly spaced transverse ridges caused by traffic actions in conjunction with lose of aggregate. They often occur in areas with heavy acceleration and deceleration traffic actions.
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Erosion and gravel loss: This occurs from a sweeping action of traffic or free flowing water across road surface. It may severely alter the cross-section of the road causing safety concerns and poor rideability.
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Pulverization: A break down of surface aggregate particles under traffic load creating excessive dust with rolling wheels. Although pulverization may not hinder the riding quality of the road surface, it may create safety hazards and discomfort both to the drivers and in areas within the vicinity.
3.3.2 Flexible pavement
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Cracking: There are three types of cracking common to flexible pavement: surface, fatigue, and movement (term used for the purpose of this paper) cracking.Surface cracking is associated with aging and deterioration of the surface bituminous layer due to shrinking and hardening. It is not associated with applied load and may appear along the full-width of the pavement. Thermal cracking, a subset of surface cracking, is common in northern regions of the US where temperatures can fall below −23 °C. Thermal cracking forms when the thermal stress on the pavement is greater than the fracture strength. Thermal cracking may also occur in milder climates if the asphalt becomes hardened due to aging or if the road was constructed with hard asphalt.Fatigue cracking is associated with traffic loading and appears along the vehicle wheel path. It is often associated with deformation along the asphalt. It is also referred to as alligator cracking because it resembles the skin of the alligator or a chicken-wire pattern. Early signs can be detected from observations of fine parallel longitudinal cracks along the wheel-paths.Movement cracking is associated with the movement of the subsurface layers such as the subgrade, concrete slab below the asphalt, culvert, or bridge joints. It typically appears transverse or longitudinal and follows the dimensions of the problematic area underneath the surface.
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Potholes: Bowl-shaped holes similar to those in unpaved roads, typically form as a result of untreated cracks. They are problematic if depth and diameter becomes greater than 25 mm and 150 mm, respectively.
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Rutting: These surface deformations occur along the wheel-path as similarly observed in unpaved roads. They are caused mainly by the deformation of the subsurface layers as a result of the surface traffic load propagating to subsurface layers.
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Swelling: An upward bulge on the pavement surface usually caused by frost action or by swelling subgrade soils. Swelling can appear as a localized bulge or a long gradual wave.
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Shoving: These defects are similar to rutting, however, they typically occur in areas where vehicles frequently stop and start. They are result of shear forces induced by traffic loading and form as localized longitudinal or transverse displacements.
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Raveling: This is the result of traffic abrasive action and is indicated by a progressively damaged surface downward into the pavement layers, such as the binder course, and aggregate loss within the binder course.
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Bleeding of asphalt: Shiny black surface caused by liquid asphalt typically migrating in hot temperatures along the pavement surface. It has a large impact on skid resistance of the asphalt.
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Polished asphalt: Wearing off of the sharp edges in the surface aggregate from traffic. It results in a smooth slippery surface and has a large impact on skid resistance of the asphalt.
3.3.3 Rigid pavement
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Cracking: In general, there are four types of cracking in rigid pavement: surface, durability, cluster, and diagonal cracking.Surface cracking is associated with aging and deterioration of the surface concrete layer and does not protrude deeply into the concrete slab. It may form as a series of random cracks, longitudinally parallel to the pavement centerline, or pop-outs of small pieces of pavement broken loose from the surface.Durability cracking forms adjacent to joints, cracks, or free edges of the pavement and is initiated at the intersection of cracks and a free edge. It usually appears as closely spaced, crescent-shaped, dark colored, hairline cracking. It is mainly attributed to the response of the material properties to freeze-thaw cycles and aggregate pore structure.Cluster cracking is a closely spaced transverse cracking occurring in groups of three or more with spacing ranging between 150-600 mm. This is more of a characteristic of continuously reinforced concrete pavements and is typically associated with changes in conditions below the surface, such as settlement within subsurface layers, poor drainage conditions, and high base friction. However, it may also form as a result of inadequate concrete thickness, lack of concrete consolidation, and construction of concrete during high temperatures. It usually occurs early in the life of the pavement.Diagonal cracking indicates an existing foundation problem (settlement or expansion) and forms in a direction oblique to the pavement centerline.
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Blow-ups: A localized upward movement of the concrete pavement surface at cracks or joints typically occurring in high temperatures and precipitation. They occur in older systems where the expansion space within the concrete pavement is insufficient for expansion. Depending on the magnitude of the blow-up, the road may have to be closed to traffic.
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Faulting: Created by a movement along the joint or a crack creating an elevation difference. The name is taken from the movement observed in nature after earthquakes, however, the cause of this type is not typically associated with earthquakes (although they may also form after earthquakes). Faulting occurs when the concrete slab losses its support due to erosion or settlement of the subsurface layers. It is one of the most prominent defects and has a direct impact on road rideability.
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Spalling: Breaking, cracking, or disintegration of the slab edges within 0.6 m of a joint or crack. Spalling is generally associated with a surface weakness within the concrete but if allowed to progress and deepen, will be an indicator of a structural weakness within the concrete.
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Punch-outs: An area enclosed by two closely spaced transverse cracks, a short longitudinal crack, and the pavement edge (resembling a box cut out on the edge of the pavement). It typically initiates from traffic loading of the transverse cracks and is also aided by corrosion of the steel within the concrete.
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Pumping: This results from water seeping into the pavement system or ejecting out of the system through the cracks or joints. In some cases it is detectable by deposits of fine material left on the pavement surface. It is caused by inadequate concrete slab thickness and erodible underlying layers.
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Joint seal damage: This results from joint deterioration, enabling a significant amount of water to infiltrate into the joint from the surface, weed growth at the joint, or intrusion of particles into the joint. It may lead to development of closely spaced transverse cracks or large numbers of interconnected cracks near the joint.
4 Traditional assessment of road surface defects
5 Overview of remote sensing methods
5.1 Remote sensing techniques
5.2 Remote sensing platforms
5.2.1 Satellite
5.2.2 Airplane
5.2.3 Unmanned aerial vehicle
5.2.4 Vehicle
6 Remote sensing methods applicable to road assessment
6.1 Unpaved roads
6.2 Paved roads
6.2.1 Visible
6.2.2 Ground penetrating radar
6.2.3 Infrared thermography
6.2.4 LiDAR and terrestrial laser scanning
6.2.5 Hyperspectral
6.2.6 Emerging techniques
6.3 Summary matrices
Distress | Visible | Airplane | UAV | Vehicle |
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Potholes | [107] | [12] | ||
Rutting | [107] | [12] | ||
Corrugations | [107] | [12] | ||
Erosion and Gravel Loss | [107] | [107] | [12] | |
Pulverization | [107] | [107] | [12] |
Distress | Visible | SAR | GPR | IR Thermography | LiDAR | TLS | Hyperspectral | Satellite | Airplane | Vehicle |
---|---|---|---|---|---|---|---|---|---|---|
Surface Cracking | [37] | [131] | [53] | [53] | ||||||
Fatigue Cracking | [121] | |||||||||
Movement Cracking | ||||||||||
Potholes | [19] | |||||||||
Rutting | [121] | [64] | ||||||||
[121] | ||||||||||
Shoving | [73] | |||||||||
Raveling | [82] | [54] | [82] | |||||||
Polished asphalt | ||||||||||
[102] |