| HOME |
PAVEMENT TREATMENT |
PAVEMENT REHABILITATION |
CONSTRUCTION
EQUIPMENTS |
FLEXIBLE PAVEMENT DISTRESSES
Today, roads are very important to the public. It is important to connecting people to go from one place to another. Modern roads are normally smoothed, paved, or otherwise prepared to allow people easy travelling. To ensure its continued efficiency and accessibility, the road network has to be maintained to high standard. Normally roads are damaged due to environment influence, vehicle load and the presents of water on road pavement.
Road defects are recognized in a few categories, these include pavement cracks, surface deformations, surface defects, patch, pothole and edge defects. Crocodile, block, longitudinal, transverse, edge crack and crescent shaped are called pavement cracks. Cracking of road pavement surface can happen in a wide variety of patterns, raging from isolated single crack to interconnected pattern extending over the entire pavement surface. The detrimental effects associated with the presence of cracks are pavement layers will loss of water-proofing, cracked material will loss of load spreading ability, loss of fines from the base course and loss of appearance.
The loss of pavement layers ability to spreading load and water-proofing will usually lead to accelerated deterioration. Some of the possible causes of cracks include:
a) Depression
b) Age embrittlement of the surfacing
c) Shrinkage
d) Reflection of cracks in underlying layers
e) Lack of construction joints
Type of cracks included:
a) Crocodile cracks - Crocodile cracks are interconnected or interlaced cracks which form a network of multi-sided blocks resembling the skin of a crocodile. The block sizes can vary and generally range from 100mm – 300mm. Crocodile cracks is a consequence of the inability of the structure to support the repeated loads due to failing of materials normally associated with increase in moisture content. The cracks in the sub base or sub grade tend to spread rapidly under rain and traffic causing blocks of surfacing to be displaced and broken up. Some of possible causes of the crocodile cracks are poor base drainage, brittle wearing course, brittle base, low modulus base and inadequate of pavement thickness.
 crocodile cracks |
b) Block cracks - Block cracks are same as crocodile cracks but the rang of cracks of the block cracks are large then crocodile crack where usually greater than 300mm and can exceed 3 meter. The cause of the block cracks are lack of joints in underlying layer, shrinkage and fatigue of underlying cemented materials and fatigue cracks in embrittled bituminous wearing course.
 |
c) Longitudinal cracks - Longitudinal cracks are cracks which are parallel to the centre line, situated at or near to the middle of the lane. Longitudinal cracks can happen singly or as series of almost parallel cracks. This cracks causes by reflection of shrinkage cracks, displacement of joints at pavement widening, reflection of joints in the underlying base and differential settlement between cut and fill.
 |
d) Edge cracks – The cracks happen at edge of road and it are crescent shaped or fairly continuous cracks, parallel to, and usually within 300mm to 1000mm. edge cracks occurs when excessive traffic loading at pavement, shoulders not exist, inadequate pavement width, poor drainage and insufficient of bearing support.
e) Crescent shaped cracks - Crescent shape cracks are cracks like half moon, normally associated with shoving and occur on bituminous layer only. Lack of bond between wearing course, low modulus base course, thin wearing course, dragging of paver during laid and high stresses due to braking are possible causes of this crack.
f) Transverse cracks - Unconnected cracks running transversely across the pavement. Normally occur when reflection of shrinkage, lack of construction joint in bituminous surfacing and reflection of joint in the underlying base.
Surface deformations
Surface deformation will occur when materials such sub grade base course changes from its original constructed profile. In some cases, road construction does not follow the specification required, such as inadequate compaction, base course or unsuitable materials. This may occur after construction due to trafficking or environmental influences.
The major types of surface deformation are:
a) Corrugation - Corrugation is a regular transverse undulation, closely spaced alternate valleys and crest with wavelengths of less than 2 m. It’s occur when compaction of base in wave form, heavy traffic on steep down grade, stopping at intersection stop light or roundabout.
b) Depression - Depression is areas within a pavement with elevations lower than the surrounding area. Settlement due to instability of embankment, differential settlement of sub grade or base materials and volume change of sub grade due to environmental influence is the causes of depression occurred.
c) Shoving - Bulging of the road surface is call shoving. It generally parallel to direction of traffic and horizontal displacement of surfacing materials. Some of the causes of shoving occur is lack of bond between asphalt surface, inadequate of pavement thickness, stop and start of vehicles at intersections and roundabout and unstable granular base reflecting through the surface.
d) Rutting -Longitudinal depression in the wheel paths which occur after repeated application of axle loading. Rutting occur when thickness of pavement is inadequate, poor of base compaction and unstable granular bases.
Surface defects
Loss of surfacing materials, loss of surface micro and macro textures are called surface defects. It has a significant influence on the serviceability and safety of pavement, especially with regard to skid resistance, maneuverability and riding quality. Surface defects included:
a) Raveling - Raveling is the progressive disintegration of the pavement surface by loose of binder or aggregate. Raveling occur when insufficient of bitumen content of road seal, poor adhesion of bitumen binder to aggregate particle due to wet aggregate and inadequate compaction or paving during wet weather.
b) Polishing - Smoothening and rounding of the upper surface of aggregate is called polishing. Polishing always occur in road paths area.
c) Bleeding - The presence of free bitumen binder on the surface resulting from upward migration of the binder is called bleeding. We can see the bleeding in the wheel paths during hot weather. Bleeding occur due to excessive application of binder with respect to the stone size and paving over excessively primed surface.
d) Delamination - Delamination is the loss of a discrete and large area of the wearing course. Poor application of tack coat, inadequate cleaning before placing of upper layers, seepage of water through asphalt and loose layer immediately underlying seal is some possible causes of delamination.
Pothole
Pothole is a hole or pit in the pavement surface resulting from the loss of wearing course, binder course and base materials. It happens when traffic breaches small pieces of the pavement surface allowing the entry of water. Loss of surface course and load associated disintegration of base also is the causes of develop pothole.
Edge Drop-offs
Edge drop-off is the difference in elevation between asphalt pavement and road shoulder. It generally occurs when the road shoulder is too narrow, inadequate resistance to erosion and abrasion of road shoulder, not having right camber of shoulders and resurfacing of pavement without resurfacing of shoulders. It’s also occurred during highway work such as resurfacing or shoulder work. When not properly addressed, drop-offs may lead to an errant vehicle losing control with a high potential for a serious accident.