IRC 19:2005 provides comprehensive specifications and code of practice for the construction and maintenance of Water Bound Macadam (WBM) layers used as sub-base, base, or surfacing courses in road pavements. It details material requirements, construction procedures, quality control measures, and maintenance practices to ensure durable and even pavement surfaces. This standard is essential for civil engineers, contractors, and highway authorities involved in road construction and rehabilitation projects using WBM technology.
Overview
IRC 19:2005 provides comprehensive specifications and code of practice for the construction and maintenance of Water Bound Macadam (WBM) layers used as sub-base, base, or surfacing courses in road pavements. It details material requirements, construction procedures, quality control measures, and maintenance practices to ensure durable and even pavement surfaces. This standard is essential for civil engineers, contractors, and highway authorities involved in road construction and rehabilitation projects using WBM technology.
Audience
Contents
Structure
The scope of IRC 19 covers specifications and standards for Water Bound Macadam (WBM) road construction, including materials, construction procedures, surface evenness, rectification of defects, and maintenance (see Preamble Table). Key points include:
| Classification | Size Range (mm) | WBM sub-base/base course (m³) | WBM surfacing course* (m³) |
|---|---|---|---|
| Grading 3 | 53 to 22.4 | 0.18 to 0.21 | 0.14 to 0.17 |
*Note: Surfacing course quantities are 80% of base course quantities due to higher binding material requirements (Clause 3.5.2).
This scope ensures uniformity in WBM construction and material usage as per IRC 19.
Sources: Preamble Table, Clause 1.2.1, Clause 3.5, Table 5
Water Bound Macadam (WBM) is defined as a pavement layer consisting of clean, crushed coarse aggregates that are mechanically interlocked by rolling. The voids between these aggregates are filled with screening and binding material with the assistance of water. WBM is laid on a prepared subgrade, sub-base, base, or existing pavement. It can serve as a sub-base, base course, or surfacing course depending on the road category. Construction must follow the specifications in the code and conform to the designated lines, grades, and cross-sections as per Clause 2.1.1.
Sources: Clause 2.1.1
Key materials specifications and quantities for Water Bound Macadam (WBM) as per IRC 19 include:
Binding Material: As per Clause 3.4, binding material is essential for WBM construction, typically stone screenings or crushable materials like moorum or gravel.
Quantities of Material: Clause 3.5 and Table 5 specify approximate quantities for a 75 mm compacted thickness of WBM sub-base/base/surfacing course per 10 m² area.
Table 5 (Excerpt):
| Coarse Aggregates | Size Range (mm) | Loose Quantity (m³) | Stone Screenings (WBM sub-base/base course m³) | Stone Screenings (WBM surfacing course m³) | Crushable Type (m³) | Loose Quantity (m³) |
|---|---|---|---|---|---|---|
| Grading 3 | 53 to 22.4 | -do- | 0.18 to 0.21 | 0.14 to 0.17 | -do- | -do- |
Note: Quantities for surfacing course (Col. 6) are 80% of those for sub-base/base (Col. 5) due to higher binding material use (Clause 3.5.2).
Material Properties: For satisfactory performance, materials should have Liquid Limit (LL) < 20, Plasticity Index (PI) < 6%, and passing 75 micron sieve < 10% (Clause 13.2).
This ensures proper gradation, binding, and durability of WBM layers.
Sources: Clause 3.4, Clause 3.5, Clause 13.2, Table 5
The key specifications for Construction Procedure in IRC 19 include guidance on material quantities and construction steps. As per Clause 3.5.3, the quantities given are for estimation only. For a 75 mm compacted thickness of Water Bound Macadam (WBM) sub-base, base, or surfacing course, Table 5 provides approximate quantities of coarse aggregates and screenings per 10 m². For example, Grading 3 coarse aggregates (size 53 to 22.4 mm) require loose quantities of 0.18 to 0.21 m³ for sub-base/base and 0.14 to 0.17 m³ for surfacing course, with screenings and crushable materials quantities adjusted accordingly. Note that surfacing course quantities are 80% of sub-base/base due to higher binding material use (Clause 3.5.2). The construction procedure details start at page 7 (Clause 4) and include steps for material preparation, laying, and compaction to ensure proper surface evenness and durability.
Sources: Clause 3.5.3, Clause 4, Clause 3.5.2, Table 5
As per IRC 19 Clause 5.1 and Table 6, the surface evenness of the Water Bound Macadam (WBM) course must be checked both longitudinally and transversely. The longitudinal profile is measured using a 3-metre straight edge. The permissible surface unevenness and undulation limits depend on the size range of coarse aggregates as follows:
| SI. No. | Size Range of Coarse Aggregates | Max. permissible Surface unevenness (mm) | Max. number of undulations >12 mm in 300 m | Max. number of undulations >10 mm in 300 m | Max. permissible transverse variation (mm) |
|---|---|---|---|---|---|
| 1. | 90-45 mm | 15 | 30 | - | 12 |
| 2. | 63-45 mm or 53-22.4 mm | 12 | - | 30 | 8 |
Additionally, per Clause 4.8.2, bituminous surfacing should be laid only after the WBM course is completely dry and before any traffic is allowed on it.
Sources: Clause 5.1, Clause 5.2, Table 6, Clause 4.8.2
The IRC 19 code addresses Rectification of Defective Construction primarily in Clause 6 under the Construction Procedure section. While the retrieved context does not provide explicit formulas or detailed tables for rectification, it indicates that quantities mentioned in Clause 3.5.3 are guides for estimation during construction. For rectification, the code likely emphasizes identifying defects, removing defective material, and reconstructing as per specifications to ensure compliance with quality standards. Since no specific formulas or tables are provided in the retrieved text, standard engineering practice involves assessing defect extent, calculating removal and replacement quantities, and ensuring proper compaction and material quality during reconstruction.
Sources: Clause 3.5.3, Clause 6 (Construction Procedure)
For construction of WBM (Water Bound Macadam) over narrow widths, as per Clause 7, the existing shoulders should be excavated to full depth and width up to the subgrade level unless a stabilized-soil sub-base is specified, in which case excavation is up to the sub-base level. The WBM construction then follows the procedure in Clause 4.
Key material quantities for 100 mm compacted WBM sub-base per 10 m² are given in Table 4:
| Coarse Aggregates | Size Range (mm) | Loose Quantity (m³) | Stone Screenings (Type A 13.2 mm) | Loose Quantity (m³) | Crushable Type (Moorum or Gravel) | Loose Quantity (m³) |
|---|---|---|---|---|---|---|
| Grading 1 | 90 to 45 | 1.21 to 1.43 | Type A 13.2 mm | 0.27 to 0.30 | LL<20, PI<6%, passing 75 micron <10 | 0.30 to 0.32 |
Surface evenness should be checked transversely at 10 m intervals using camber templates as per Clause 22.4. Defective areas must be scarified and reworked over at least 10 m² as per Clause 6.
This ensures proper bonding and compaction over narrow widths during widening operations.
Sources: Clause 7, Clause 4, Clause 22.4, Clause 6, Table 4, Clause 3.5.1
Maintenance of WBM Wearing Courses per IRC 19 involves timely interventions under three heads: periodic patching of potholes with removal of ruts and depressions, blinding of the surface, and surface renewals as per Clause 8.1. Surface irregularities exceeding tolerances (see Table 6, not provided) require scarifying the full thickness over at least 10 m², reshaping or replacing material, and recompaction per Clause 6. Depressions must not be filled with screenings or binding material. For surface profile checks, camber templates at 10 m intervals are used (Clause 22.4). For material quantities in a 75 mm compacted WBM surfacing course, Table 5 provides approximate volumes of coarse aggregates and screenings per 10 m², e.g., for Grading 3 (53-22.4 mm), stone screenings quantity is 0.14 to 0.17 m³, which is 80% of base course quantities due to higher binder content needed (Clause 13.2).
Sources: Clause 8.1, Clause 6, Clause 22.4, Clause 13.2, Table 5
As per IRC 19 Clause 3.5 and related sub-clauses, approximate quantities of materials for Water Bound Macadam (WBM) layers are given for specific compacted thicknesses and areas. For a 100 mm compacted thickness of WBM sub-base per 10 m², Table 4 provides loose quantities of coarse aggregates and screenings by grading and size. For example, Grading 1 (90 to 45 mm) requires 1.21 to 1.43 m³ of coarse aggregates and 0.27 to 0.30 m³ of Type A 13.2 mm stone screenings. Similarly, for a 75 mm compacted thickness (Table 5), quantities are proportionally less, with surfacing course quantities being 80% of base course quantities due to more binding material use (Clause 3.5.2). These quantities are guides for estimation (Clause 3.5.3).
Sources: Clause 3.5, Clause 3.5.1, Clause 3.5.3, Table 4, Table 5
The key references for IRC 19 include various IRC, IS, and BS standards that form the basis of provisions in this standard as per Clause 1.3.1. Important referenced standards are:
| Standard | Title |
|---|---|
| IRC:SP:16-2004 | Guidelines for Surface Evenness of Highway Pavements (First Revision) |
| IS 460:Part 1 : 1985 | Specification for test sieves: Part 1 cloth test sieves (Third Revision) |
| IS 460:Part 2 : 1985 | Specification for test sieves: Part 2 Perforated plate test sieves (Third Revision) |
| IS 460:Part 3 : 1985 | Specification for test sieves: Part 3 Methods of examination of apertures of test sieves (Third Revision) |
| IS 2386:Part 1-1963 | Method of Test for Aggregates for Concrete - Part 1: Particle Size and Shape (Reaffirmed 2002 Amds. 3) |
| IS 2386:Part 3-1963 | Method of Test for Aggregates for Concrete - Part 3: Specific gravity, density, voids, absorption and bulking (Reaffirmed 2002) |
| IS 2430:1986 | Methods for Sampling of Aggregates for Concrete (First Revision) (Reaffirmed 2000) |
| IS 5640:1970 | Method of test for determining aggregate impact value of soft coarse aggregates (Reaffirmed 1998 Amds.1) |
| BS 1047:1983 | Specification for air-cooled blast furnace slag aggregate for use in construction (Replaced by EN 12620) |
These references provide specifications for materials, test methods, and construction guidelines relevant to Water Bound Macadam (WBM) pavement construction. The standard also includes symbols and abbreviations such as LL (Liquid Limit), PI (Plasticity Index), and WBM (Water Bound Macadam) as per Clause 1.2.1.2.
This list is essential for ensuring compliance with material quality and construction procedures in WBM pavement works.
Sources: Clause 1.3.1, Clause 1.2.1.2
Frequently Asked
For Water Bound Macadam (WBM) construction, the IRC 19 specifies three gradings of coarse aggregates with corresponding size ranges and sieve gradings as per Table 2. The types and sizes are:
| Grading No. | Size Range and Compacted Thickness | Sieve Designation (IS 460) | % Passing |
|---|---|---|---|
| 1 | 90 mm to 45 mm (100 mm thick) | 125 mm | 100 |
| 90 mm | 90-100 | ||
| 63 mm | 25-60 | ||
| 45 mm | 0-15 | ||
| 22.4 mm | 0-5 | ||
| 2 | 63 mm to 45 mm (75 mm thick) | 90 mm | 100 |
| 63 mm | 90-100 | ||
| 53 mm | 25-75 | ||
| 45 mm | 0-15 | ||
| 22.4 mm | 0-5 | ||
| 3 | 53 mm to 22.4 mm (75 mm thick) | 63 mm | 100 |
| 53 mm | 90-100 | ||
| 45 mm | 65-90 | ||
| 22.4 mm | 0-10 | ||
| 11.2 mm | 0-5 |
Each grading corresponds to a specific compacted layer thickness: 100 mm for grading 1 and 75 mm for gradings 2 and 3 (Clause 4.3.2). Screenings of type A are used with grading 1, and type B with grading 3 (Clause 3.3.2). Uniform gradation without segregation is essential during spreading (Clause 4.3.2).
Sources: Clause 3.3.2, Table 2, Clause 4.3.2
The surface evenness of a WBM (Water Bound Macadam) course should be measured and controlled as per Clause 5 of IRC 19. The longitudinal profile is checked using a 3-metre long straight edge placed at the middle of the carriageway. The permissible surface unevenness limits depend on the size range of coarse aggregates used, as detailed in Table 6. For example, for 90-45 mm aggregates, the maximum permissible longitudinal unevenness is 15 mm, with up to 30 undulations exceeding 12 mm allowed in any 300-metre length. The transverse profile is checked using a camber template, with a maximum permissible variation of 12 mm for 90-45 mm aggregates. The WBM course must be completely dry before bituminous surfacing and before allowing any traffic (Clause 4.8.2).
Sources: Clause 4.8.2, Clause 5.1, Clause 5.2, Table 6
As per IRC 19 Clause 4.7.1, the recommended procedure for applying binding material in WBM layers is to apply it uniformly and slowly in two or more successive thin layers after the screenings are laid. After each application, the surface should be copiously sprinkled with water, and the resulting slurry must be swept into the voids using hand or mechanical brooms. This is followed by rolling with an 80-100 kN roller, applying water to the roller wheels to wash off any binding material stuck to them. The process of spreading binding material, sprinkling water, sweeping, and rolling should continue until a slurry wave forms ahead of the roller wheels, ensuring proper filling of voids and bonding.
Sources: Clause 4.7.1, Clause 3.4.1, Clause 3.4.2
According to IRC 19, defective WBM layers with surface irregularities beyond permissible tolerances or contamination by sub-grade soil must be rectified by scarifying the full thickness of the affected area, reshaping with added material, or removing and replacing with fresh material, followed by recompaction as per Clause 4. The treated area should be at least 10 m². Importantly, depressions must not be filled with screenings or binding material (Clause 6). Additionally, before laying WBM on existing un-surfaced roads, scarification, reshaping, strengthening weak spots, and removal of corrugations and potholes are required (Clause 4.1.2). For WBM over bituminous surfaces, scarifying or adequate bonding and drainage measures are necessary (Clause 2.1.2).
Sources: Clause 6, Clause 4.1.2, Clause 2.1.2
To ensure the longevity of Water Bound Macadam (WBM) surfaces, timely maintenance is crucial as per IRC 19. The key maintenance practices include:
These measures help maintain the structural and functional performance of the WBM surfacing (Clause 8.1). Additionally, when laying WBM over existing bituminous surfaces, it is advisable to remove the bituminous layer completely or provide 50 mm x 50 mm furrows at 1 m intervals at 45° to ensure proper bonding and drainage, preventing premature failures (Clause 4.1.3).
Sources: Clause 8.1, Clause 4.1.3
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