Distresses in Pavement and probable repair remedies

Distresses in Pavements and Probable Repair Remedies

Summary of Distresses

Type of Distress	Symptoms	Probable Cause	Possible Treatment
Surface Defects
1. Fatty Surface	Collection of binder on surface	Excessive binder in premix, spray or tack coat; loss of cover aggregates; excessively heavy axle loads	Sand blinding; open-graded premix; liquid seal coat; burning off excess binder; removal of affected area
2. Smooth Surface	Slippery	Polishing of aggregates under traffic or excessive binder	Resurfacing with surface dressing or premix carpet
3. Streaking	Presence of alternate lean and heavy lines of bitumen	Non-uniform application of bitumen or application at low temperature	Application of new surface
4. Hungry Surface	Loss of aggregates or presence of fine cracks	Use of less bitumen or use of absorptive aggregates	Slurry seal or fog seal
5. Bleeding of Asphalt	Slippery	Excess of asphalt while mixing	Sand blinding
Cracks
1. Hairline Crack	Short and fine cracks at close intervals on the surface	Insufficient bitumen, excessive filler, or improper compaction	Treatment depends on whether pavement is structurally sound or unsound. For structurally sound pavements, fill cracks with low-viscosity binder, slurry seal, or fog seal depending on crack width. Unsound cracked pavements require strengthening or rehabilitation treatments.
2. Alligator Cracks	Interconnected cracks forming a series of small blocks	Weak pavement, unstable subgrade or lower layers, excessive overloads, or brittleness of binder
3. Longitudinal	Cracks in straight line along the road	Poor drainage, shoulder settlement, weak joint between adjoining spreads of pavement layers, or different frost heaves
4. Edge Crack	Crack near and parallel to pavement edge	Lack of support from shoulder, poor drainage, frost heave, or inadequate pavement width
5. Shrinkage Cracks	Cracks in transverse direction or interconnected cracks forming large blocks	Shrinkage of bitumen layers with age
6. Reflection Cracks	Symptomatic cracks over joints and cracks in underlying pavement	Due to joints and cracks in the underlying pavement layer
Deformation
1. Slippage	Formation of crescent-shaped cracks pointing in direction of wheel thrust	Unusual wheel thrust, lack or failure of bond between surface and lower courses	Removal of surface layers in affected area and replacement with fresh material
2. Rutting	Longitudinal depression in wheel tracks	Heavy channelized traffic, inadequate compaction, poor stability of materials, or heavy bullock cart traffic	Filling depressions with premix material
3. Corrugations	Formation of regular undulations	Lack of stability in mix, vehicle spring oscillations, or faulty laying of surface course	Scarification and relaying of surfacing, or cutting high spots and filling low spots
4. Shoving	Localized bulging of pavement surface along crescent-shaped cracks	Unstable mix, lack of bond between layers, heavy start-stop movements, or negotiation of curves/gradients	Removing material up to firm base and relaying a stable mix
5. Shallow Depressions	Localized shallow depressions	Presence of inadequately compacted pockets	Filling with premix materials
6. Settlements and Upheaval	Large deformations of pavement	Poor compaction of fills, poor drainage, inadequate pavement strength, or frost heave	Excavate and redo weak fill; strengthen pavement if inadequate strength is the cause
Disintegration
1. Stripping	Separation of bitumen from aggregates in presence of moisture	Hydrophilic aggregates, inadequate mix composition, continuous water contact, poor bond, poor compaction	Spread and compact heated sand (for surface dressing); replace with fresh bituminous mix containing anti-stripping agents (other cases)
2. Loss of Aggregates	Rough surface with loss of aggregates in some portions	Ageing/hardening of binder, stripping, poor bond, insufficient binder, brittleness	Application of liquid seal, fog seal, or slurry seal depending on damage extent
3. Raveling	Failure of binder to hold aggregates, shown by pock marks or coded areas	Poor compaction, poor bond, insufficient binder, brittleness	Application of cutback covered with coarse sand, slurry seal, or premix renewal coat
4. Pot-Hole	Bowl-shaped holes, usually after rain	Ingress of water, lack of bond between surfacing and WBM base, insufficient bitumen	Filling with premix material or penetration patching
5. Edge Breaking	Irregular breaking of pavement edges	Water infiltration, poor lateral support from shoulders, inadequate edge strength	Cut affected area into regular sections and rebuild; simultaneously construct proper shoulders

Timely identification and appropriate repair of pavement distresses significantly extend service life, improve safety, and reduce long-term maintenance costs. Always ensure proper drainage and use anti-stripping agents where moisture is a concern.

Types of Pavement Failures and Distresses

1) Structural Failure

Collapse of pavement components of such magnitude that the pavement becomes incapable of sustaining imposed traffic loads.

Factors Responsible for Structural Distress

a) Preparation of Foundation

i) Strength

Even with macadam or asphalt base courses, insufficient foundation strength leads to failure under transmitted traffic stresses. Weak areas often show a crazed crack pattern.

Newly constructed flexible pavements may hide weaknesses due to non-uniform grading, clay pockets, or inadequate compaction. A practical test involves driving a roller (equivalent to surfacing weight) over the foundation and noting deflections. However, this does not replicate repetitive traffic loading or detect design flaws.

Weaknesses must be remedied by replacing unsound material or providing adequate pavement thickness relative to subsoil bearing capacity.

ii) Shape

Mixture composition and layer thickness are interrelated—thicker layers require larger aggregates. Foundations must be regular transversely and longitudinally, involving filling depressions or removing high spots.

Low areas should be raised with material from the same temperature group. Nominal aggregate size depends on fill depth; multiple grades may be needed for deeper sections.

High spots can be treated by scarifying or breaking out with compressors.

iii) Permeability

Porous foundations combined with open-textured surfacing allow water percolation, weakening the subgrade. Proper surface dressing prevents this.

iv) Compaction

Mixtures require proper compaction for satisfactory performance under traffic. Steel-wheeled and pneumatic-tyred rollers reduce voids, with bitumen acting as a lubricant. Viscosity at rolling temperature is critical, influenced by filler content and aggregate shape/texture.

• Density standards are achieved through rigorous lab testing. Asphalt concrete must meet specified density and void limits.
• Specifying roller numbers based solely on tonnage/area is misleading; rolling temperature and material type govern effectiveness. Trial patches determine optimal rolling temperatures.
• Heat loss depends on thickness, wind, and air temperature. Sufficient roller capacity ensures compaction within temperature limits.
• Roller procedure: Longitudinal forward/reverse passes with slight overlaps, varying pass lengths to avoid surface marks. Continuous movement prevents indentations.
• Three-wheeled rollers start with rear rollers; narrow rollers risk hard-to-remove indentations.
• Field trials and core tests establish qualitative compaction standards—continue rolling until no further reaction and uniform texture.

b) Shear

Occurs when cohesion and internal friction are insufficient in the base/subgrade. Characterised by upheaval outside wheel paths and surface cracking.

Often due to poor shear strength of pavement mixes. Proper shoulder design reduces edge failures.

Edge Breaking: Pavement edges break due to lack of shoulder support or heavy edge tracking.

Longitudinal Cracks: Single or multiple cracks parallel to the centerline, caused by horizontal movement from lack of friction or differential settlement of plastic subgrades.

c) Consolidation

Surface distortion from consolidation of paving layers, leading to rutting in under-designed pavements. Primarily occurs in subgrade, less in base.

d) Cracking

Causes:

• Structural failure (rutting without adjacent upheaval – consolidation of lower layers)

• Rolling too hot
• Excessive water on roller wheels
• Reflection from underlying layers
• Fatigue damage

Types of Cracking:

• Cracking without pattern
• Cracking of unstable mix
• Reflection cracking (regular pattern from underlying rigid/semi-rigid base)
• Alligator cracking

Class I Alligator Cracking: Interconnected cracks forming a map pattern; edges not raised/spalled, no rocking under load (fatigue from resilient base/subgrade).

Cracks edges not raised – Type 1

Class II Alligator Cracking: Interconnected cracks; edges raised/spalled, pieces rock under load (severe distress, structural inadequacy, or shrinkage/swelling soils like black cotton soil).

Cracks edges raised and water-filled – Type 2

Observe for one full seasonal cycle before applying crack filler or slurry.

e) Adverse Groundwater Conditions

High groundwater weakens subgrade, causing localised failures even in otherwise satisfactory pavements. Remove water at source; minor resurfacing offers only temporary relief.

Pot-Holes

1) Isolated Pot-Holes: Local distress, soft spots, or water entrapment.

Water stored in local pothole via ravelled area

2) Pot-Holes Associated with Cracking: Cracked pieces dislodge under traffic; severe distress, end-of-life pavement, structural inadequacy, lack of binder, excessive voids, poor drainage.

Pot-holes are highly dangerous and require immediate repair to prevent further deterioration.

f) Heating and Drying

Aggregate storage conditions affect drying efficiency. Wet or recently washed aggregates are hardest to dry and heat, impacting mix quality.

2) Functional Failure

Pavement cannot perform its intended function without inducing excessive stresses in vehicles due to surface roughness, despite no structural collapse.

Functional Failures

a) Surface Defects

• Segregation: Poor mixing/rolling or excessive hand raking creates density/permeability variations.
• Dragging: Open texture laterally; caused by insufficient thickness or high paver speed.
• Weathering: Dry, oxidised appearance from old surfacing or insufficient bitumen.
• Bleeding: Excess bitumen on surface (wheel paths); too much/soft bitumen.

b) Accumulation of Binders

Excess binder from previous dressings softens new layers. Remove by heating/planing before overlay.

c) Joint Failures

Poorly filled or raised joint compounds exacerbate reflective cracking. Remove and refill with compatible fine material.

d) Adhesion Failure

Laying on wet, contaminated, or overly smooth surfaces leads to slippage/stripping under traffic. Provide a key coat.

e) Temperature Issues

Low-viscosity base course bitumen can mobilise under hot surface course. Differential cooling causes stripping. Careful joint overlapping prevents textural differences.

f) Roughness

Incorrect rolling (temperature-sensitive materials) or paver issues (tamper wear, screed corrosion) cause uneven texture.

g) Ravelling

Loss of coarse/fine aggregates outside wheel paths.

Causes: Stripping, aggregate degradation, insufficient bitumen, bitumen oxidation.

General Causes of Pavement Distresses

• 1) Overloaded vehicles
• 2) High repetitions of loads
• 3) High tyre pressure
• 4) Climatic & environmental conditions (volume changes from wetting/drying, freeze-thaw)
• 5) Improper drainage – Saturated subgrade is the greatest enemy of pavement stability.
• 6) Disintegration of paving materials – Breakdown generates fines, loses interlock, accelerates pothole formation.
• 7) Poor construction practices – Subgrade rutting, dirty aggregates, inadequate control.
• 8) Lack of maintenance – Untimely crack/joint sealing allows water infiltration.

Quiescent load stress in potholes (dynamic impact):

$$\sigma_1 = \sigma \sqrt{\frac{2h}{e}}$$

Where $$h$$ can be expressed as $$h = \frac{V^2}{2g}$$ in terms of velocity.