Introduction

• Maintenance of road reduces petrol consumption and wear and tear of vehicles.
• Also provide comfort to passenger.

Requirements of Good Pavement

• Sufficient thickness to distribute the wheel load stresses to a safe value on the sub-grade soil.
• Structurally strong to withstand all types of stresses imposed upon it.
• Adequate coefficient to friction to prevent skidding of vehicles.
• Smooth surface to provide skidding of vehicles.
• Produce least noise from moving vehicles.
• Dust proof surface so that traffic safety is not impaired by reducing visibility.
• Impervious surface, so that sub-grade soil is well protected, and long design life with low maintenance cost.

Necessity of Maintenance of Highway

• To prevent accidents.
• To maintain all the components of road in better working condition ex. Pavement, shoulder, drains, etc.
• To provide safe and convenient movement of passenger.
• To maintain road in best possible condition for smooth driving.
• To increase life of road.
• To keep safety for road users.

Causes of Failure Flexible Pavement

Flexible Pavements

Flexible pavements will transmit wheel load stresses to the lower layers by grain to grain transfer through the points of contact in the granular structure.

Failure of Flexible Pavement can be caused by following reason

• Excessive load application.
• Inadequate stability.
• Loss of course materials.
• Loss of binding action between highway materials.
• Use of low quality material in different layers.
• Inadequate wearing course.
• Inadequate strength of material.
• Inadequate drainage of rainwater from different layers.
• Improper compaction of layers of flexible pavement.
• Environmental factors like heavy rain, frost action, etc.

Types of Failure of Flexible Pavement

1. Subgrade Failure of Flexible pavements

• Improper compaction of subgrade soil.
• Improper drainage in subgrade or inadequate camber to subgrade layer.

2. Wearing Course Failure

• Improper bonding between top course highway material.
• Less quantity of binding material is used during construction.
• Aggregates used in wearing course is not clean which affects binding.

3. Failure of Base Course

• Improper drainage
• Heavy load
• Improper compaction
• Material used is of low quality in base course.

Types of Defects of Flexible Pavement

1. Cracks
2. Rutting and Shoving
3. Pot Holes and Patching

Cracks

Following are types of cracks observed in flexible pavement:

• Alligator Cracking
• Longitudinal Cracking
• Block Cracking
• Edge Cracking
• Centre Cracking

Alligator Cracking

General Description

• Series of interconnected cracks.
• Many sided, sharp angled, usually longest side < 1 feet.
• Initially appears a longitudinal crack.

Causes

• Ageing of binder or initial over heating leads to brittleness of binder.
• Inadequate pavement thickness or excessive overloading or both.
• Unstable subgrade or lower layers.

Treatment

• Cracks should be filled with low viscosity binder.
• Slurry seal or sand bituminous premix patching can be used to fill wide cracks.
• Cut back or an emulsified bitumen or fog seal can be bloomed into the cracks and lightly filled with sand to prevent the picking up of the binder by the traffic.

Longitudinal Cracking

General Description

• These cracks are relatively parallel to pavement centre line, may appear either at the joint between the pavement and the shoulder or at the joint between two paving lanes.

Causes

• Variation in temperature.
• Week joint between adjoining layers of the pavement.

Treatment

Treatment depends on whether pavement remains structurally sound or not, if structurally sound then treatment is done as follow:

• Fill cracks with bituminous binder.
• A slurry seal or sand.
• Bituminous premix patching for wide cracks.

Block Cracking

General Description

• These cracks appear as interconnected cracks forming blocks of square or rectangular shape on pavement surface.
• The size of the block cracking varies from 1000 sq.cm to 10000 sq.cm

Causes

• Inadequate pavement thickness and unstable condition of subgrade and lower layers.
• Shrinkage of bituminous layer itself with age.
• Ageing and brittleness of binding material.

Treatment

• The block cracking should be repaired by laying a interface treatment followed by giving layer as per original existing surface.

Edge Cracking

General Description

These are fairly continuous cracks, parallel to and usually up to 0.5m from the edge of pavement. Edge cracks if not repaired in time lead to edge breaking and lane to shoulder drop off and separation occurs.

Causes

• Lack of lateral support from shoulder.
• Poor drainage and frost heavy condition.
• Settlement or yielding of the underlaying material.
• Non provision of extra width of pavement.

Treatment

• Lack of lateral condition and give lateral support to pavement.
• Seal the cracks with either of these depending on severity level and width of cracks as follows:

1. Low viscosity binder
2. A slurry seal

Centre Cracking

Description

• The cracking pattern appears all along the centre line of pavement.

Causes

• Improper or weak joint between adjoining, spreads all along the centre line of the pavement.
• Different moisture conditions on both sides of the pavement.
• Improper design of pavement with reference to camber.

Treatment

• It is better to take full precautions while constructing a pavement.
• This can be rectified by sealing the cracks with slurry seal and or fog seal depending on width of the cracks.

Rutting and Shoving

Rutting

• Rutting is a longitudinal surface depression or groove in the wheel path.

Causes

• Weak pavement and heavy channelized traffic.
• Improper mix design and lack of stability.
• Inadequate compaction of  underlaying layers during construction.

Treatment

• Fill with premix open/dense graded material and compact to the desired levels after applying a tack coat.
• Rutting is due to subgrade failure then excavation and rectification of subgrade is  done.

Shoving

• It is a form of plastic movement resulting into localized bulging of surface.

Causes

• Lack of stability in mix of surface or base course.
• Pushing action by wheels of heavy traffic at time of acceleration and deacceleration.

Treatment

• Filling the depression with premix materials after applying suitable tack coat.
• Remove the material in the affected area down to a firm base and laying a suitable premix patch.

Pot Holes

These are bowl shaped holes of various sizes in the surface layer or extending into the base course.

Causes

• Localized disintegration of materials.
• Ingress of water in the pavement through cracks in surface course.
• Poor bond between surface and base course layers.
• Less bitumen content in localized areas or too thin bituminous surface.

Treatment

• Treatment is done by patch work or patch repairs.
• To fill pot holes with the premix open/dense graded patching or even penetration patching and followed by compaction.