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IRC 7 : 2017Standard Specifications and Code of Practice for Road Bridges — Foundations and Substructure — Wearing Coat

Q: What is the primary purpose of a wearing coat on a road bridge?

The primary purpose of a wearing coat on a road bridge is to provide a durable and functional riding surface for traffic, protecting the underlying bridge deck structure from the damaging effects of traffic loads, weather, and environmental factors. It also contributes to the overall safety and comfort of road users by providing adequate skid resistance and a smooth driving experience. Additionally, it acts as a protective layer against water ingress, de-icing salts, and other corrosive agents, thereby extending the service life of the bridge.

Q: What are the most common types of wearing coats specified in this IRC code?

The IRC code specifies several common types of wearing coats, including asphaltic concrete, mastic asphalt, and surface dressings. Asphaltic concrete, a widely used option, offers good durability and rideability. Mastic asphalt provides excellent impermeability and durability, making it suitable for demanding conditions. Surface dressings are often used as a cost-effective solution for lower-traffic roads or as a maintenance treatment. The code also mentions cementitious and polymer-modified coatings for specific applications.

Q: How is the appropriate bitumen grade selected for an asphaltic concrete wearing coat?

The selection of the appropriate bitumen grade is crucial and depends significantly on the climatic conditions of the location where the bridge is situated. For hot weather conditions, bitumen with a higher penetration grade (e.g., 60/70 or 80/100) is typically recommended to maintain flexibility. Conversely, in cold weather, a bitumen with a lower penetration grade (e.g., 40/50 or 30/40) is preferred to prevent the mix from becoming brittle. The code also provides guidance on considering traffic intensity and expected service life in this selection.

Q: What are the key considerations for the design of asphaltic concrete mixes?

The design of asphaltic concrete mixes involves ensuring a balance between stability, durability, and workability. Key considerations include the selection and gradation of aggregates to achieve a dense and interlocking structure, determining the optimal bitumen content for adequate coating and binding without excess, and controlling the void content within specified limits. The code refers to standard mix design methods and specifies criteria for parameters like voids in mineral aggregate (VMA) and voids filled with bitumen (VFB) to ensure the mix performs well under traffic loads and environmental stresses.

Q: What are the essential steps during the construction of an asphaltic concrete wearing coat?

The construction of an asphaltic concrete wearing coat involves several critical stages. It begins with thorough preparation of the bridge deck surface, including cleaning and applying a tack coat for proper adhesion. The asphalt mix is then transported to the site at the correct temperature and laid uniformly using paving machines. Compaction follows immediately, typically using steel-wheeled rollers, to achieve the specified density and eliminate air voids. Proper construction of joints and ensuring the correct temperature during laying and compaction are also vital for a successful outcome.

Q: When is mastic asphalt a preferred choice for bridge wearing coats?

Mastic asphalt is a preferred choice for bridge wearing coats in situations demanding high impermeability, excellent durability, and resistance to aggressive environments. It is particularly suitable for bridge decks exposed to de-icing salts, aggressive chemicals, or areas with heavy and slow-moving traffic. Its ability to form a seamless, voidless layer also makes it highly resistant to water penetration, which is crucial for protecting the underlying concrete or steel structure. The code specifies minimum thicknesses for mastic asphalt layers based on these demanding conditions.

Q: What quality control measures are important during the construction of wearing coats?

Rigorous quality control is essential throughout the construction of wearing coats. This includes testing the properties of incoming materials like bitumen and aggregates to ensure they meet the specified standards. During mix production, tests are conducted to verify the mix design and ensure consistency. In-situ testing is crucial to check parameters like the temperature of the mix during laying and compaction, the achieved density, and the surface regularity. Adherence to these quality control measures ensures the wearing coat performs as intended throughout its service life.

Q: What is the role of surface dressing in bridge maintenance?

Surface dressing serves as a cost-effective maintenance treatment for bridge wearing coats, particularly for lower-traffic bridges or as a rejuvenation layer. It involves applying a binder (bitumen) followed by a single or double layer of chippings (aggregates). The primary benefits include sealing minor surface cracks, preventing further water ingress, and restoring a degree of skid resistance. While it provides a protective layer, its durability and performance are generally lower than that of asphaltic or mastic asphalt wearing coats.

Q: How often should bridge wearing coats be inspected and maintained?

Regular inspections are crucial for identifying potential issues and ensuring the longevity of bridge wearing coats. Routine visual inspections should be carried out at least annually, or more frequently after significant weather events or heavy traffic use. A more detailed structural inspection of the wearing coat and its interface with other bridge elements should be conducted periodically, typically every 2-3 years. Preventive maintenance, such as crack sealing and pothole repair, should be undertaken promptly as soon as these issues are detected to prevent them from escalating and causing more significant damage.

Q: Can the weight of the wearing coat impact the bridge superstructure?

Yes, the weight of the wearing coat contributes to the overall dead load of the bridge superstructure. While standard wearing coats are designed to be within typical load parameters, engineers must consider the cumulative dead load during the initial bridge design phase. For older bridges or those with lighter designs, the addition or replacement of a wearing coat might necessitate a structural assessment to ensure the bridge can safely support the added weight. The code implicitly assumes that the wearing coat will not overload the structure if applied as per specifications.

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AASHTO LRFD Bridge Design Specifications (USA) · EN 13108 - Bituminous mixtures - Material specifications (Europe) · BS EN 13108 - Bituminous mixtures - Material specifications (UK)

CurrentFrequently UsedCode of PracticeTransportation · Bridges and Bridge Engineering

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IRC 7:2017 is the Indian Standard (IRC) for standard specifications and code of practice for road bridges — foundations and substructure — wearing coat. This IRC code addresses the critical aspect of bridge deck protection and performance by outlining specifications for wearing coats. It guides engineers on selecting appropriate materials, such as asphaltic concrete, mastic asphalt, or specialized polymer-modified coatings, considering factors like traffic load, climate, and intended service life. The code details construction methodologies, including surface preparation, layer thickness, compaction, and joint construction, emphasizing quality control measures at each stage. Furthermore, it delves into inspection, maintenance, and repair strategies to ensure the long-term effectiveness of the wearing coat, thereby extending the overall life of the bridge superstructure and providing a safe and comfortable riding surface for users.

This code provides standard specifications and a code of practice for the design, construction, and maintenance of wearing coats on road bridges. It covers material selection, application methods, durability considerations, and quality control for various types of wearing coat systems to ensure a durable and functional bridge deck surface.

Quick Reference — IRC 7:2017 Bridge Foundations

Standard specifications and code of practice for road bridges — foundations. Design loads, scour, settlement.

✓ Verified 2026-04-28

Reference	Value	Clause
Founding depth — open foundation	below maximum scour level + 2 m	Cl. 706.1.1
Founding depth — well foundation	below maximum scour level + 2.67 m or 2 × scour	Cl. 708.2
Founding depth — pile foundation	≥ 6 m below scour level (in scourable soil)	Cl. 709.2
Maximum scour depth — empirical (D)	1.34 × (Q² / Ksf)^(1/3)	Cl. 703.2 (Lacey)
Bearing capacity — factor of safety	≥ 2.5 against ultimate	Cl. 706.2
Permissible settlement — total	75 mm (typical bridge pier)	Cl. 706.4 (refers IS 1904)
Permissible settlement — differential	1/300 of pier spacing	Cl. 706.4
Concrete grade — substructure RCC	M30 minimum	Cl. 703.5
Concrete grade — well steining	M25 minimum	Cl. 708.4
Cover — concrete on soil/water side	75 mm minimum	Cl. 703.6
Steining thickness — well foundation	≥ ⅛ of inside diameter (or 0.6 m min)	Cl. 708.2.4
Bottom plug — well foundation	≥ ½ of well diameter or 1.5 m	Cl. 708.2.7
Pile diameter — minimum bored cast-in-situ	1000 mm (highway bridges)	Cl. 709.2.3
Pile group spacing — minimum c/c	2.5 × diameter (end-bearing)	Cl. 709.5
Pile group spacing — friction piles	3 × diameter	Cl. 709.5
Pile load test — initial	2.5 × design load	Cl. 709.4.4
Pile load test — routine	1.5 × design load	Cl. 709.4.4
Test piles — minimum number	1 % of total piles or 2 (whichever more)	Cl. 709.4.4
Pile cap thickness — minimum	1.5 × pile diameter	Cl. 709.7
Lateral capacity — pile in soft soil	10 % of vertical capacity (typical)	Cl. 709.6

⚠ Section VII Foundations — companion to IRC 6 (loads), IRC 78 (Substructures), IRC 21 (concrete) / IRC 24 (steel).

Overview

Status: Current
Usage level: Frequently Used
Domain: Transportation — Bridges and Bridge Engineering
Type: Code of Practice

International equivalents

AASHTO LRFD Bridge Design Specifications (USA)EN 13108 - Bituminous mixtures - Material specifications (Europe)BS EN 13108 - Bituminous mixtures - Material specifications (UK)

Typically used with

IS 73 IS 110

Also on InfraLens for IRC 7

18Key values 6Tables 10FAQs

Practical Notes

! Proper surface preparation, including cleaning and tack coat application, is paramount for the adhesion and longevity of any wearing coat.

! The choice of bitumen grade should be carefully considered based on the ambient temperature range during construction and service life.

! Adequate compaction is essential to achieve the desired density and reduce the risk of future distress like rutting and water ingress.

! Joint construction in asphaltic wearing coats needs special attention to prevent premature failure and water infiltration.

! For bridges in seismic zones, the wearing coat design should consider potential movements and vibrations.

! Mastic asphalt offers excellent impermeability and is suitable for areas prone to de-icing salt attack or aggressive environments.

! Polymer-modified bitumen (PMB) can enhance the performance of asphaltic wearing coats, offering improved resistance to temperature fluctuations and fatigue cracking.

! Regular visual inspections should be conducted to identify early signs of wear, cracking, or ravelling, enabling timely preventive maintenance.

! The use of anti-skid aggregates or specialized surface treatments can significantly improve the friction characteristics of the wearing coat, especially in high-traffic areas or at approaches.

! During construction, maintaining the correct laying and compaction temperatures is critical to achieving the designed mix properties.

! Consideration should be given to the impact of the wearing coat's weight on the bridge superstructure, especially for older or lighter bridges.

! The contractor must demonstrate compliance with quality control procedures and testing frequencies as specified in the code.

! For surface dressing, ensuring uniform application of binder and aggregate is vital for its effectiveness and durability.

! The interface between the wearing coat and expansion joints or drainage scuppers requires careful detailing to prevent ingress of water and debris.

! Alternative wearing coat materials, such as epoxy-based or polyurethane systems, may be considered for specific requirements, but their use should be guided by specialized standards or manufacturer recommendations.

! The wearing coat should be designed to provide adequate skid resistance, especially in areas with high rainfall or frequent braking by vehicles.

Frequently referenced clauses

Cl. 1.1Introduction

Cl. 2.1Types of Wearing Coats

Cl. 3.1Materials for Asphaltic Concrete Wearing Coats

Cl. 4.1Design of Asphaltic Concrete Mixes

Cl. 5.1Construction of Asphaltic Concrete Wearing Coats

Cl. 6.1Mastic Asphalt Wearing Coats

Cl. 7.1Other Types of Wearing Coats

Cl. 8.1Quality Control and Testing

Cl. 9.1Maintenance and Repair

Bridge EngineeringWearing CoatAsphaltic ConcreteMastic AsphaltIRC CodesRoad BridgesSubstructurePavementConstructionMaintenanceQuality ControlIRC

Engineer's Notes

In Practice — Editorial Commentary

When IRC 7 is your governing code

IRC 7 (2017) is a constituent of the Standard Specifications and Code of Practice for Road Bridges series, covering Foundations, Substructure and Wearing Coat aspects that are common across bridge types. It works alongside IRC:5:2015 (general features), IRC:6:2017 (loads), IRC:78:2014 (foundations + substructure), IRC:83:2018 (direct foundations), and IRC:112:2020 (concrete bridges). For wearing coat aspects specifically, IRC 7 ties into bituminous + concrete wearing-course specs.

Use IRC 7 when you are: - Designing or constructing road bridge substructure (piers, abutments, pier-caps) - Specifying wearing coat on the bridge deck (typically bituminous over RCC deck or PCC) - Cross-referencing substructure specifications across the IRC bridge series - Doing DPR for a road bridge (Part of the IRC 5+6+7+78+83+112 stack) - Designing expansion / hinge joint hardware at substructure level - Specifying bearing pads, fixed/expansion bearings within the substructure-deck interface - Inspecting + maintaining wearing course on existing road bridges

IRC 7 has a narrower scope than other bridge codes — it focuses on the wearing-coat + substructure boundary. For comprehensive bridge design, it must be read alongside: - IRC:5:2015 for general features - IRC:6:2017 for loads - IRC:78:2014 for foundations/substructure design - IRC:112:2020 for concrete bridges - IRC:24:2010 for steel bridges

Wearing coat + substructure design

Wearing coat — purpose: 1. Riding surface — provides smooth, durable surface for vehicular traffic 2. Waterproofing — prevents water ingress into deck slab → corrosion of reinforcement 3. Wear protection — protects deck concrete from tyre abrasion + chemical attack 4. Drainage — provides cross-fall for water removal

Wearing coat types: - Bituminous wearing coat: Standard for NH road bridges. Typically 50-75 mm thick dense bituminous concrete (BC) per IRC:107:2013 or modified bitumen mixes. - Concrete wearing coat: Used on some heavy-traffic urban bridges. M40+ grade, 50-75 mm thick, with proper joints. - Slab decks (PSC / RCC): wearing coat applied directly on deck top surface. - Steel decks (orthotropic): asphalt wearing coat 50-65 mm typical, on waterproof membrane.

Substructure key elements: 1. Pier: vertical structural element transferring deck load to foundation 2. Pier cap (pier head): flares from pier shaft to support deck girders / bearings 3. Bearings: elastomeric / pot / spherical bearings transferring load + accommodating movement 4. Abutment: end-support, carries deck + retains approach embankment 5. Bearing seat: specially-detailed concrete area under each bearing 6. Drainage from deck: drain pipes through pier cap or down the pier face 7. Inspection access: ladders, walkways, manholes for substructure inspection

Pier cap detailing: - Thickness varies; typically 1.0-1.5 m for medium bridges; up to 2.5 m for large bridges - Top surface slopes for water drainage (away from bearings) - Bearing seats with drip-tray detailing - Reinforcement: heavy bottom + top bars to handle bending; tie bars for shear - Concrete grade M30 minimum; M40 for severe exposure

Bearing types: - Elastomeric bearings: rubber pads with steel plates; for small-medium bridges; relatively cheap, requires periodic replacement - Pot bearings: rubber pot in steel cup; medium-large bridges; better load capacity - Spherical bearings: for large bridges + curved bridges; accommodate rotation in two directions - Roller / rocker bearings: older bridges; now superseded - Selection: based on load + movement + rotation requirements

Joints between deck + substructure: - Expansion joints: allow thermal + creep + shrinkage movement of deck. Detail per IRC:SP-77:2008 - Hinge joints: allow rotation only (no translation). Used on segmental + box-girder bridges. Detail per IRC:19:2005 - Articulation joints: sliding bearings + dowel bars for shear transfer

Reference values + specifications

Concrete grades: - Substructure (piers, pier caps, abutments): M30 minimum for NH; M25 for SH/district - Severe exposure (marine / industrial): M40-M45 with extra durability measures - Wearing coat (concrete type): M40 minimum, durable mix - Wearing coat (bituminous): per IRC:107:2013 — typically DBM + BC

Reinforcement: - Fe 500 or Fe 500D primary - Mild steel for less critical applications - Cover requirements per IRC:112:2020 + IS 456: 75 mm to bottom face (severe exposure) - Spacing per code; main bars + distribution + ties + stirrups

Bearing pad design (elastomeric): - Load capacity: 300-1000 kN per pad typical - Shear modulus: 0.8-1.2 MPa per IS 800 specification - Dimensions: typically 200-400 mm width, 30-60 mm thickness with internal steel laminations - Service life: 20-30 years; periodic inspection mandatory

Deck wearing coat (bituminous): - DBM base layer: 50 mm typical, per IRC:SP-53:2010 - Bituminous concrete wearing: 25-50 mm thick per IRC:107:2013 - Modified bitumen (CRMB / PMB) for high-traffic NH bridges - Waterproof membrane: mandatory between deck slab + bitumen — typically polymer-modified asphalt membrane or sheet membrane, 1.5-3 mm thick

Drainage: - Cross-slope: 2.5-3 % from carriageway crown to edges - Edge collection: longitudinal drain at carriageway edge, leading to vertical drain pipes through pier cap - Vertical pipes: typically 100-150 mm Ø, well-spaced; discharge clear of substructure - Drainage from approach: separate handling per IRC:SP-13:2004

Expansion joints: - Movement range varies (cumulative thermal + creep + shrinkage) - For medium span: 25-50 mm movement - For long span: 100-200+ mm movement - Types: strip seal (small), finger plate, modular (large) - Detail per IRC:SP-77:2008 - Inspection + replacement: every 10-20 years typical

Inspection access: - Pier cap walkway: 1 m wide minimum, with handrails - Ladders + manholes for pier interior (where applicable) - Light fittings for low-light inspection areas - Drain manhole access at deck-level for cleaning

Construction tolerances: - Pier alignment: ± 25 mm of design - Pier cap level: ± 10 mm of design - Bearing seat level: ± 5 mm of design - Pier verticality: 1:500 of height (= 1 mm out of plumb per 500 mm of height) - Concrete cover: must meet minimum + allowance for placement; ± 10 mm acceptable

Companion codes (must pair with)

IRC:5:2015 — General Features of Design (the parent of the IRC 5+6+7+78 family)
IRC:6:2017 — Loads + Stresses for Road Bridges
IRC:78:2014 — Foundations + Substructures (full design framework)
IRC:83:2018 — Direct (Shallow) Foundations (cross-references substructure)
IRC:112:2020 — Concrete Road Bridges (current; replaces IRC:21)
IRC:24:2010 — Steel Road Bridges
IRC:21:2000 — RCC Road Bridges (superseded by IRC:112 but useful reference)
IRC:19:2005 — Hinge + Expansion Joints in Concrete Bridges
IRC:SP-77:2008 — Expansion Joints for Road Bridges
IRC:107:2013 — Bituminous Concrete (BC) Wearing Course
IRC:SP-53:2010 — Modified Bitumen + Bituminous Mix Specifications
IRC:115:2014 — FWD-based Structural Evaluation
IS 456:2000 — Plain + Reinforced Concrete
IS 800:2007 — General Construction in Steel
IS 1893 (Part 1) — Earthquake Resistant Design
IS 11512 — Code of Practice for Use of Sealants in Bridges
IS 11663 — Materials for Bridge Construction
IS 13311 — Non-Destructive Testing of Concrete
MoRTH Specifications for Road and Bridge Works — Section 700 (Special Structures: Bridges) + Section 800 (Bituminous Pavement)

Common pitfalls / what reviewers flag

1. Wearing coat directly on deck without waterproof membrane. Water reaches deck rebar; corrosion accelerates; deck distress within 5-10 years. Mandatory waterproof membrane between deck + wearing coat. 2. Insufficient cross-fall for drainage. Deck drains poorly; ponding on bridge; aquaplaning risk + accelerated wearing-coat distress. Cross-slope 2.5-3 % from crown to edge. 3. Bearing pads not regularly inspected. Pad cracks / hardens / displaces; load transfer compromised. Annual inspection + replacement at 20-30 year cycle. 4. No drip-tray detail at bearing seat. Rain runs down pier face onto bearing; pad degrades + corrosion of bearing plates. Drip detail mandatory. 5. Expansion joint deteriorates without replacement. Joint leaks; water reaches deck-substructure interface; corrosion + spalling. Replacement cycle 10-20 years; mandatory inspection. 6. Inadequate cover to reinforcement. Cover < 50-75 mm in severe exposure; chloride / sulphate ingress; rebar corrosion. Code-specified cover + verification by site engineer. 7. No inspection access. Walkway / ladders missing; routine inspection difficult; deterioration unnoticed. Inspection access designed-in from start. 8. Vertical drain pipes too few. Drainage capacity inadequate during heavy rain; water sits on deck. Adequate number + spacing per IRC:SP-13:2004. 9. Pier cap concrete grade too low. M25 used where M30+ required; durability inadequate. Specification per IRC:112:2020. 10. Construction tolerances exceeded. Pier alignment / verticality off; bearing seats unsupported; load transfer compromised. Strict QC + survey at every stage. 11. No corrosion-protection on bearings. Steel bearings without protection; corrosion + seizing within 5-10 years. Galvanising + sealants. 12. Approach slab missing / not designed. No transition between rigid bridge + flexible approach; differential settlement creates 'bump at end of bridge'. Approach slab per IRC:75:2015 approach-embankment design. 13. Joint between deck + substructure water-leaks. Seal degrades; water enters substructure interior; corrosion of internal rebar. Sealant per IS 11512; periodic inspection + reseal.

Where it sits in bridge-project lifecycle

Road bridge project — IRC 7 touchpoints:

1. Feasibility: Bridge type selection (slab / box girder / steel truss); substructure type per spans + soil conditions. 2. DPR: - Substructure design per IRC:78:2014 + IRC:83:2018 - Pier shape + dimensions; abutment design - Bearing selection + sizing - Wearing coat specification (bituminous typically) - Drainage layout (cross-fall, edge collection, vertical drains) - Expansion + hinge joint design per IRC:19:2005 + IRC:SP-77:2008 3. Detailed design: - Pier reinforcement detailing per IS 456 + IRC:112:2020 - Pier cap details including bearing seats + drip trays - Bearing pad specifications (load, movement, rotation) - Expansion joint hardware specifications - Inspection walkway + access 4. Tender + BOQ: concrete, reinforcement, formwork, bearings, joints, wearing coat, waterproof membrane, drainage, joints, signage. 5. Construction: - Pier construction + curing - Pier cap + bearing seat - Bearing installation (pre-cast or cast-in-place) - Deck construction (separately per superstructure type) - Waterproof membrane application - Wearing coat laying - Expansion joint installation - Drainage piping 6. Quality control: - Concrete strength verification (cube samples + cores) - Reinforcement cover verification (X-ray / cover-meter) - Bearing pad verification (load test on representative sample) - Wearing coat density + thickness verification 7. Pre-opening: - Settlement monitoring baseline - Bearing function verification - Drainage functional test - Approach slab tied in 8. Operations + maintenance: - Annual visual inspection of substructure + wearing coat + bearings - 5-year detailed inspection per IRC:SP-37:2010 - Bearing pad replacement every 20-30 years - Expansion joint replacement every 10-20 years - Wearing coat resurfacing every 8-15 years - Long-term: cathodic protection (if corrosion advanced); structural rehabilitation

IRC 7 sits at the substructure-wearing-coat interface of every road bridge project — invoked through the full bridge series specifications and operations manuals.

International Equivalents

Similar International Standards

AASHTO LRFD Bridge Design Specifications (USA)

MediumCurrent

EN 13108 - Bituminous mixtures - Material specifications (Europe)

MediumCurrent

BS EN 13108 - Bituminous mixtures - Material specifications (UK)

MediumCurrent

Key Differences

≠

Key Similarities

≈

Parameter Comparison

Parameter	IS Value	International	Source
Aggregate Gradation
Bitumen Grade
Mix Design Method
Voids in Mineral Aggregate (VMA)
Voids Filled with Bitumen (VFB)

⚠ Verify details from original standards before use

Key Values18

Quick Reference Values

minimum thickness asphaltic concrete50 mm

maximum aggregate size asphaltic concrete19 mm (for binder course)

bitumen content range asphaltic concrete4.0 - 6.0 % by weight of mix

minimum voids in mineral aggregate asphaltic concrete15 %

minimum voids filled bitumen asphaltic concrete75 %

bitumen grade for hot weather60/70 or 80/100 penetration grade

bitumen grade for cold weather40/50 or 30/40 penetration grade

minimum thickness mastic asphalt20 mm

filler material mastic asphaltHydrated lime or Portland cement, typically 10-15%

minimum temperature for laying asphaltic concrete100°C

minimum temperature for compaction asphaltic concrete70°C

traffic lane width for standard wearing coat3.5 m

allowable surface regularity deviation4 mm in 3 m

minimum curing period for cementitious coatings7 days

recommended anti-skid coefficientNot explicitly stated, but implied through material selection and surface finish.

maximum permissible cracks per sqm2 cracks (minor hairline)

minimum binder content for surface dressing1.0 litre/sqm

aggregate size for surface dressing6 mm or 10 mm

Key Formulas

Conceptual reference to calculations involving stability and flow values, as per IRC:22 or similar mix design codes, to ensure the structural integrity of the asphalt mix.

VMA (%) = 100 - (Gs * (100 - Pba)) / Gb

VFB (%) = (VMA - Va) / VMA * 100

Bt = 0.035A + 0.65 (where Bt is the percentage of bitumen by weight of dry aggregate and A is the percentage of aggregate passing the 0.075 mm sieve).

Tables & Referenced Sections

Key Tables

Gradation of Aggregates for Asphaltic Concrete

Properties of Bitumen for Wearing Coats

Mix Design Criteria for Asphaltic Concrete

Minimum Thickness of Mastic Asphalt Layers

Recommended Bitumen Content for Surface Dressing

Acceptable Limits for Surface Regularity

Frequently Asked Questions10

What is the primary purpose of a wearing coat on a road bridge?+

The primary purpose of a wearing coat on a road bridge is to provide a durable and functional riding surface for traffic, protecting the underlying bridge deck structure from the damaging effects of traffic loads, weather, and environmental factors. It also contributes to the overall safety and comfort of road users by providing adequate skid resistance and a smooth driving experience. Additionally, it acts as a protective layer against water ingress, de-icing salts, and other corrosive agents, thereby extending the service life of the bridge.

What are the most common types of wearing coats specified in this IRC code?+

The IRC code specifies several common types of wearing coats, including asphaltic concrete, mastic asphalt, and surface dressings. Asphaltic concrete, a widely used option, offers good durability and rideability. Mastic asphalt provides excellent impermeability and durability, making it suitable for demanding conditions. Surface dressings are often used as a cost-effective solution for lower-traffic roads or as a maintenance treatment. The code also mentions cementitious and polymer-modified coatings for specific applications.

How is the appropriate bitumen grade selected for an asphaltic concrete wearing coat?+

The selection of the appropriate bitumen grade is crucial and depends significantly on the climatic conditions of the location where the bridge is situated. For hot weather conditions, bitumen with a higher penetration grade (e.g., 60/70 or 80/100) is typically recommended to maintain flexibility. Conversely, in cold weather, a bitumen with a lower penetration grade (e.g., 40/50 or 30/40) is preferred to prevent the mix from becoming brittle. The code also provides guidance on considering traffic intensity and expected service life in this selection.

What are the key considerations for the design of asphaltic concrete mixes?+

The design of asphaltic concrete mixes involves ensuring a balance between stability, durability, and workability. Key considerations include the selection and gradation of aggregates to achieve a dense and interlocking structure, determining the optimal bitumen content for adequate coating and binding without excess, and controlling the void content within specified limits. The code refers to standard mix design methods and specifies criteria for parameters like voids in mineral aggregate (VMA) and voids filled with bitumen (VFB) to ensure the mix performs well under traffic loads and environmental stresses.

What are the essential steps during the construction of an asphaltic concrete wearing coat?+

The construction of an asphaltic concrete wearing coat involves several critical stages. It begins with thorough preparation of the bridge deck surface, including cleaning and applying a tack coat for proper adhesion. The asphalt mix is then transported to the site at the correct temperature and laid uniformly using paving machines. Compaction follows immediately, typically using steel-wheeled rollers, to achieve the specified density and eliminate air voids. Proper construction of joints and ensuring the correct temperature during laying and compaction are also vital for a successful outcome.

When is mastic asphalt a preferred choice for bridge wearing coats?+

Mastic asphalt is a preferred choice for bridge wearing coats in situations demanding high impermeability, excellent durability, and resistance to aggressive environments. It is particularly suitable for bridge decks exposed to de-icing salts, aggressive chemicals, or areas with heavy and slow-moving traffic. Its ability to form a seamless, voidless layer also makes it highly resistant to water penetration, which is crucial for protecting the underlying concrete or steel structure. The code specifies minimum thicknesses for mastic asphalt layers based on these demanding conditions.

What quality control measures are important during the construction of wearing coats?+

Rigorous quality control is essential throughout the construction of wearing coats. This includes testing the properties of incoming materials like bitumen and aggregates to ensure they meet the specified standards. During mix production, tests are conducted to verify the mix design and ensure consistency. In-situ testing is crucial to check parameters like the temperature of the mix during laying and compaction, the achieved density, and the surface regularity. Adherence to these quality control measures ensures the wearing coat performs as intended throughout its service life.

What is the role of surface dressing in bridge maintenance?+

Surface dressing serves as a cost-effective maintenance treatment for bridge wearing coats, particularly for lower-traffic bridges or as a rejuvenation layer. It involves applying a binder (bitumen) followed by a single or double layer of chippings (aggregates). The primary benefits include sealing minor surface cracks, preventing further water ingress, and restoring a degree of skid resistance. While it provides a protective layer, its durability and performance are generally lower than that of asphaltic or mastic asphalt wearing coats.

How often should bridge wearing coats be inspected and maintained?+

Regular inspections are crucial for identifying potential issues and ensuring the longevity of bridge wearing coats. Routine visual inspections should be carried out at least annually, or more frequently after significant weather events or heavy traffic use. A more detailed structural inspection of the wearing coat and its interface with other bridge elements should be conducted periodically, typically every 2-3 years. Preventive maintenance, such as crack sealing and pothole repair, should be undertaken promptly as soon as these issues are detected to prevent them from escalating and causing more significant damage.

Can the weight of the wearing coat impact the bridge superstructure?+

Yes, the weight of the wearing coat contributes to the overall dead load of the bridge superstructure. While standard wearing coats are designed to be within typical load parameters, engineers must consider the cumulative dead load during the initial bridge design phase. For older bridges or those with lighter designs, the addition or replacement of a wearing coat might necessitate a structural assessment to ensure the bridge can safely support the added weight. The code implicitly assumes that the wearing coat will not overload the structure if applied as per specifications.

QA/QC Inspection Templates

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IRC 7 : 2017Standard Specifications and Code of Practice for Road Bridges — Foundations and Substructure — Wearing Coat

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Link points to Internet Archive / others. Not hosted by InfraLens. Details

AASHTO LRFD Bridge Design Specifications (USA) · EN 13108 - Bituminous mixtures - Material specifications (Europe) · BS EN 13108 - Bituminous mixtures - Material specifications (UK)

CurrentFrequently UsedCode of PracticeTransportation · Bridges and Bridge Engineering

PDF Google Compare IRC Portal

Link points to Internet Archive / others. Not hosted by InfraLens. Details

Quick Reference — IRC 7:2017 Bridge Foundations

Standard specifications and code of practice for road bridges — foundations. Design loads, scour, settlement.

✓ Verified 2026-04-28

Reference	Value	Clause
Founding depth — open foundation	below maximum scour level + 2 m	Cl. 706.1.1
Founding depth — well foundation	below maximum scour level + 2.67 m or 2 × scour	Cl. 708.2
Founding depth — pile foundation	≥ 6 m below scour level (in scourable soil)	Cl. 709.2
Maximum scour depth — empirical (D)	1.34 × (Q² / Ksf)^(1/3)	Cl. 703.2 (Lacey)
Bearing capacity — factor of safety	≥ 2.5 against ultimate	Cl. 706.2
Permissible settlement — total	75 mm (typical bridge pier)	Cl. 706.4 (refers IS 1904)
Permissible settlement — differential	1/300 of pier spacing	Cl. 706.4
Concrete grade — substructure RCC	M30 minimum	Cl. 703.5
Concrete grade — well steining	M25 minimum	Cl. 708.4
Cover — concrete on soil/water side	75 mm minimum	Cl. 703.6
Steining thickness — well foundation	≥ ⅛ of inside diameter (or 0.6 m min)	Cl. 708.2.4
Bottom plug — well foundation	≥ ½ of well diameter or 1.5 m	Cl. 708.2.7
Pile diameter — minimum bored cast-in-situ	1000 mm (highway bridges)	Cl. 709.2.3
Pile group spacing — minimum c/c	2.5 × diameter (end-bearing)	Cl. 709.5
Pile group spacing — friction piles	3 × diameter	Cl. 709.5
Pile load test — initial	2.5 × design load	Cl. 709.4.4
Pile load test — routine	1.5 × design load	Cl. 709.4.4
Test piles — minimum number	1 % of total piles or 2 (whichever more)	Cl. 709.4.4
Pile cap thickness — minimum	1.5 × pile diameter	Cl. 709.7
Lateral capacity — pile in soft soil	10 % of vertical capacity (typical)	Cl. 709.6

⚠ Section VII Foundations — companion to IRC 6 (loads), IRC 78 (Substructures), IRC 21 (concrete) / IRC 24 (steel).

Overview

Status: Current
Usage level: Frequently Used
Domain: Transportation — Bridges and Bridge Engineering
Type: Code of Practice