Road Surface Defects and Repairs

Module 2: Road Surface Defects and Repairs

1. Common Road Surface Defects

Road surfaces deteriorate due to traffic loads, weather, and aging. Key defects include:

• Potholes – Deep, localized holes caused by water infiltration and traffic stress.

• Cracking – Includes:

• Longitudinal cracks (along traffic lanes due to poor construction or fatigue).

• Transverse cracks (across the road from temperature changes).

• Alligator cracks (interconnected cracks resembling reptile skin, indicating structural failure).

• Rutting – Channel-like depressions in wheel paths from repeated heavy vehicle loads.

• Surface Wear – Loss of skid resistance and aggregate exposure due to abrasion.

Impact: Defects reduce safety, increase maintenance costs, and shorten road lifespan.

2. Inspection and Defect Reporting Procedures

Regular inspections ensure timely repairs and prevent escalation:

• Visual Surveys – Routine checks for visible damage (cracks, potholes, deformation).

• Machine-Assisted Inspections – Laser scanners or drones for large-scale assessments.

• Defect Classification – Categorizing severity (e.g., Low/Medium/High risk).

• Reporting Methods – Using:

• Digital systems (GIS mapping, mobile apps like Confirm or FixMyStreet).

• Standardized forms (recording location, size, and recommended action).

• Response Prioritization – Urgent defects (e.g., deep potholes) are repaired first.

Best Practice: Follow Well-Managed Highway Infrastructure (WMHI) guidelines for consistency.

3. Repair Techniques

Selection depends on defect type, budget, and traffic disruption:

A. Patching

• Throw-and-roll (temporary cold-lay patches for quick fixes).

• Excavation and reinstatement (permanent repairs using hot-mix asphalt).

B. Surface Dressing

• Spraying bitumen emulsion + chippings to seal and restore skid resistance.

C. Micro-Asphalt

• Thin slurry mix (bitumen, aggregates, additives) for surface renewal.

D. Resurfacing

• Full-depth reconstruction for severely damaged roads.

Key Factors:

• Traffic management (lane closures, diversions).

• Curing time (cold-mix vs. hot-mix asphalt).

• Durability (micro-asphalt lasts ~10 years; patching is short-term).

4. Materials Used in Road Repairs

Sustainability Trends:

• Recycled asphalt (RAP) for eco-friendly repairs.

• Self-healing asphalt (experimental, contains steel fibers).

Key Takeaways for Learners:

• Identify defects early to prevent costly failures.

• Choose repair methods based on defect severity and traffic needs.

• Material selection impacts longevity and cost-effectiveness.

A. Potholes

• Cause: Water infiltration + freeze-thaw cycles weaken subsurface layers; traffic dislodges material

• Risk: Vehicle damage, accidents, especially for motorcycles

• Stages:

• Initial cracking → Water penetration → Base erosion → Surface collapse

B. Cracking

• Longitudinal: Runs parallel to traffic flow (poor joint construction or pavement fatigue)

• Transverse: Perpendicular to traffic (thermal contraction or reflective cracking)

• Alligator/Crocodile: Interconnected web-like cracks (structural failure of base layers)

• Edge Cracking: Road shoulders (poor drainage or lack of lateral support)

C. Rutting

• Cause: Repeated heavy axle loads deform asphalt layers

• Types:

• Wheel-Track Rutting: Channels in traffic lanes

• Shoving: Wavelike distortion at intersections (braking/acceleration forces)

D. Surface Wear

• Raveling: Aggregate loss due to poor binder adhesion

• Bleeding: Excess bitumen creates slippery surfaces

• Polishing: Smoothing of aggregate (reduces skid resistance)

2. Inspection and Defect Reporting Procedures

Systematic monitoring ensures timely interventions:

A. Inspection Methods

• Walkover Surveys: Detailed visual checks with measurement tools

• Windshield Surveys: Drive-through inspections for initial screening

• Automated Systems:

• Laser Profilers: Measure rut depth/profile

• Friction Testers: Assess skid resistance (e.g., Griptester)

B. Defect Classification

C. Reporting Protocols

1. Location: GPS coordinates or chainage markers

2. Photographic Evidence: Scale references (e.g., ruler in images)

3. Priority Scoring: Risk matrix (likelihood × consequence)

4. Digital Tools:

• Highway Condition Reporting (HCR) apps

• GIS Mapping for asset management

3. Repair Techniques

A. Patching

• Throw-and-Roll:

• Process: Fill with cold-mix asphalt + compact by vehicle tires

• Use: Temporary repairs (24-72hr cure time)

• Semi-Permanent:

• Process: Square-cut excavation + hot-mix asphalt + vibratory roller

• Standards: Follow Manual of Contract Documents for Highway Works (MCHW)

B. Surface Dressing

1. Bitumen Spray: 1.4-1.8 kg/m² of binder (e.g., C40B emulsion)

2. Chipping Spread: 6-10mm aggregates (pre-coated for adhesion)

3. Rolling: 2-3 passes for embedment

C. Micro-Asphalt

• Slurry Mix: Bitumen emulsion + fine aggregates + cement additives

• Application:

• Type 1: 10-15mm thickness (preventive maintenance)

• Type 2: 20-30mm (structural restoration)

D. Advanced Techniques

• Infrared Thermal Repair: Heats existing asphalt for seamless patches

• Full-Depth Reclamation: Pulverizes road base for complete rebuild

4. Materials Used in Road Repairs

A. Asphalt Mixes

B. Concrete

• Rigid Pavement Mix:

• 30MPa strength for heavy traffic

• Dowel bars for load transfer

• Fast-Setting:

• 4-6hr cure time (e.g., rapid-strength cement)

C. Composite Materials

• Geosynthetics: Grids to reinforce base layers

• Polymer-Modified Bitumen: Enhances flexibility in cold climates

D. Eco-Friendly Options

• Recycled Asphalt Pavement (RAP): Up to 30% reclaimed material

• Porous Asphalt: Allows water drainage (SUDS compliance)

Key Takeaways

• Defect Identification: Recognize early signs (e.g., fine cracks → alligatoring).

• Method Selection: Match repair technique to defect severity (e.g., micro-asphalt for surface wear).

• Material Science: Hot-mix for longevity; cold-mix for rapid fixes.

Practical Exercise:

• Field Simulation: Use VR/360° images to classify defects and propose repairs.

• Lab Demo: Compare compaction methods for cold vs. hot-mix asphalt.