Pavement distresses are distortions in the pavement surface and the subgrade either due to poor design or external factors. Distresses shorten the lifespan of a pavement and pose a danger to the road users or causes discomfort. This is a paper on the different types of road distresses, causes, and the mitigation measures which can be taken to remedy the distresses.
Rutting
Rutting is the accumulation of slow permanent deformation due to continuous densification of pavement layers caused by the shear displacement of the subgrade. Shearing causes uplifting on the sides of the rut. Rutting occurs along the tracks of heavy vehicles on a pavement and becomes evident after rains when they get filled up with water. There are two types of rutting; subgrade rutting and mix rutting. Mix rutting is caused by poor compaction and mix design during construction. As a result, only the pavement surface gets depressed while the subgrade remains unaffected. In subgrade rutting, the subgrade gets depressed, and the pavement dips into the subgrade ruts along the wheel path. Rutting is dangerous during rainy seasons as it causes hydroplaning of vehicles and affects steering across a rut.
Lateral deformation of pavement surface or subgrade due to loading can be caused by inadequate compaction of the HMA layer. As a result, the pavement may experience continued compaction under traffic loads. Poor pavement structure and Poor mix design such as high asphalt levels, excessive mineral filler, and inadequate angular aggregate particles may cause subgrade rutting (Coastal Road Repair, 2014).
Severely rutted pavements should be studied to ascertain the cause of failure. Applying a leveling course and a structural overlay can be used to treat ruts in a pavement.
Potholes
Potholes are caused by fatigue cracking. Interconnected fatigue cracks dislodge asphalt lumps which are then knocked loose by passing vehicles over time. A pothole has sharp edges and is vertically placed on the surface layer. Moisture penetration to the pavement via a pothole causes more damage to the surface and subgrade layers.
Potholes are treated through permanent or temporary fills. Permanent fills are done by cutting out a rectangular patch around the pothole that is then painted with a bituminous binder. A bitumen bound material is filled into the patch and compacted. A temporary fill involves cleaning the pothole and then filling it with a compactible material which is laid cold then compacted (Cornwall.gov.uk, 2014).
Alligator fatigue
Alligator failure occurs in areas of heavy traffic loading. Alligator fatigue is evidenced by interconnected cracks caused by poor compaction of the base or subgrade or poor drainage. Angled longitudinal cracks interconnect form a pattern like an alligator skin. Alligator cracking is caused primarily by traffic loading. Traffic overloading occurs when the base and the subbase are weak and cannot support the surface layer. The surface layer cracks because of lack of a solid base and hence cannot support designed loads. Harsh environmental conditions such a poor drainage and heavy spring thaw weaken the subgrade. Alligator cracking can also be caused by stripping off the aggregate at the surface due to its poor adhesion with the asphalt. Stripping reduces effective pavement thickness and its loading capacity which leads to cracking.
Alligator cracking can be treated by sealing the cracks to prevent further entry of moisture into the subgrade. Small portions of affected pavement can also be repaired by replacing the base with a new one and introducing an asphalt surface (Wolf's Asphalt Paving Blog, 2014).
Bleeding
Bleeding occurs when asphalt melts in hot weather filling aggregate voids. This creates a thin sticky asphalt film that is shiny and glossy. The film reduces skid resistance during wet conditions that can result in accidents. Bleeding can be caused by the use of an HMA mix with excessive asphalt, lack of enough air spaces for asphalt expansion in hot weather, and excessive use of asphalt during bituminous surface treatments.
Minor cases of bleeding can be repaired by the action of coarse sand on the excessive asphalt binder. For severe bleeding, excess asphalt can be scrapped off by the use of a motor grader or removal by a heater planer (Oregonstate.edu, 2014).
Depression
Depression occurs when parts of a pavement have lower elevations than the rest of the pavement. Depressions are visible during rainy seasons as they fill up with water and may cause vehicles to hydroplane. They are caused by poor compaction during construction whereby the basegrade settles later or by frost heave.
Depressions are repaired by first digging out the poor subgrade and replacing. A patch is then put over the corrected subgrade (Oregonstate.edu, 2014).
Block Cracking
Block cracks are interconnected cracks which slice the pavement into rectangular pieces. Block cracks range from 0.1m2 to 9m2. Block cracking causes road roughness and allow infiltration of moistures into the subgrade which affects the whole pavement. Block cracking is caused by cyclic contraction and expansion of the HMA and the asphalt binder's inability to expand and contract due to aging and poor mix design (Oregonstate.edu, 2014).
Block cracking can be repaired by use of crack seals for cracks less than a half inch wide or by raveling of crack edges. For severe cracking with over half inch width, the cracked pavement portions are removed and replaced with an overlay.
Longitudinal Cracking
Longitudinal cracking is a fatigue cracking where cracks formed are parallel to the centerline of the pavement. Longitudinal cracking causes roughness and degradation of the subbase by moisture. Longitudinal cracking is caused by poor and weak joints locations, reflective cracks from underlying layers, top-down cracking, and HMA fatigue.
Longitudinal cracking can be repaired with crack seal for cracks less than half an inch wide. For severe cracks wider than half an inch, the pavement layer is removed and replaced with an overlay (Oregonstate.edu, 2014).
Shoving
Shoving is a plastic movement exhibited by ripples or waves across the pavement surface and perpendicular to traffic flow. Shoving occurs at points where traffic stops or starts. Shoving causes roughness and discomfort to road users. Shoving is primarily caused by starting and stopping of traffic. Other contributing factors include low stiffness HMA layer due to poor design or moisture infiltration into the subgrade.
Shoving can be repaired by removal of distorted parts of the pavement and replacing them using patches. For large shoved areas, the pavement is removed and repaired with an overlay (Oregonstate.edu, 2014).
References
Coastal Road Repair . (2014). Rutting. Coastal Road Repair. n.p. Retrieved from http://www.coastalroadrepair.com/Knowledgebase/Rutting.aspx
Cornwall.gov.uk. (2014). Potholes. CornWall Council. Retrieved from http://www.cornwall.gov.uk/transport-and-streets/roads-highways-and- pavements/highway-maintenance/potholes/
Oregonstate.edu. (2014). 7 Flexible Pavement Distress. Oregon State University. Retrieved from http://classes.engr.oregonstate.edu/cce/spring2014/ce492/Modules/09_pavement_evaluati on/09-7_body.htm#bleeding
Wolf's Asphalt Paving Blog. (2014).What to Do When You See Alligator Cracking in Asphalt. Wolf Paving. Retrieved from http://www.wolfpaving.com/blog/what-to-do-when-you- see-alligator-cracking-in-asphalt
