IRC 19:2005 outlines detailed guidelines and specifications for constructing and maintaining Water Bound Macadam (WBM) layers used in road sub-base, base, or surfacing courses. It covers material standards, construction techniques, quality assurance methods, and upkeep procedures to guarantee long-lasting and smooth pavement surfaces. This code is vital for engineers, contractors, and highway authorities engaged in road building and restoration utilizing WBM technology.
Overview
IRC 19:2005 outlines detailed guidelines and specifications for constructing and maintaining Water Bound Macadam (WBM) layers used in road sub-base, base, or surfacing courses. It covers material standards, construction techniques, quality assurance methods, and upkeep procedures to guarantee long-lasting and smooth pavement surfaces. This code is vital for engineers, contractors, and highway authorities engaged in road building and restoration utilizing WBM technology.
Audience
Contents
Structure
This section defines the extent of IRC 19, detailing standards for Water Bound Macadam (WBM) pavement construction including materials, procedures, surface smoothness, defect correction, and maintenance. It specifies use on sub-base, base, and surfacing courses with a typical compacted thickness of 75 mm. Material quantities per 10 m² for standard thicknesses are outlined, along with definitions of symbols and SI units to maintain uniformity.
Water Bound Macadam is described as a pavement layer composed of clean, crushed coarse aggregates interlocked through rolling. Voids are filled with screenings and binding agents with water assistance. It is applied over prepared subgrade or existing pavement and serves various pavement layers depending on road classification. Construction must adhere to specified lines, grades, and cross-sections.
Details the essential materials for WBM construction including binding materials like stone screenings or crushable substances such as moorum or gravel. It specifies approximate quantities for a 75 mm compacted thickness and mandates material properties like Liquid Limit below 20, Plasticity Index under 6%, and limited fines passing 75 micron sieve for durability.
Provides guidance on construction steps including estimation of material quantities, preparation, spreading, and compaction. It emphasizes that quantity figures are estimates and highlights procedures ensuring proper surface evenness and structural integrity.
Describes measurement and control of surface evenness longitudinally using a 3-metre straight edge and transversely with camber templates. Specifies permissible unevenness and undulation limits based on aggregate size, and mandates that bituminous surfacing should occur only after the WBM layer is fully dry.
Outlines approaches for identifying and rectifying faulty WBM layers including scarifying defective zones, material replacement, reshaping, and recompaction. Emphasizes adherence to specified standards to maintain quality and durability.
Explains procedures for constructing WBM over narrow widths, including excavation of shoulders to required depth and following standard construction methods. Material quantities for 100 mm compacted layers are specified, along with surface smoothness checks and defect correction measures.
Details essential maintenance activities such as pothole patching, removal of depressions, surface blinding, and renewals. Stresses use of camber templates for monitoring and stipulates that depressions should not be filled with screenings or binding materials.
Presents approximate material volume requirements for WBM layers at different compacted thicknesses including 75 mm and 100 mm. Provides guidance on loose quantities of aggregates and screenings based on grading and emphasizes that these estimates assist in planning and execution.
Lists important IRC, IS, and BS standards referenced within IRC 19 that govern specifications, testing, and construction practices for WBM pavements. Includes standards on test sieves, aggregate testing methods, and guidelines ensuring material and construction compliance.
Frequently Asked
IRC 19 specifies three gradings of coarse aggregates based on size ranges and sieve gradations. Grading 1 covers 90 to 45 mm aggregates for 100 mm thick layers, grading 2 includes 63 to 45 mm for 75 mm thickness, and grading 3 consists of 53 to 22.4 mm for 75 mm thickness. Each grading uses designated sieve sizes with specified percentage passing ranges to ensure uniform gradation and compaction quality.
Surface evenness is assessed longitudinally with a 3-metre straight edge placed mid-carriageway and transversely using camber templates. Permissible unevenness limits vary according to aggregate size grading. The WBM surface must be completely dry before applying bituminous surfacing and before permitting traffic to ensure proper bonding and durability.
Binding material should be spread uniformly in multiple thin layers after laying screenings. Each application is followed by thorough water sprinkling and sweeping of the slurry into voids using brooms. Compaction is performed with an 80-100 kN roller, with water applied to roller wheels to remove adhered binder. This process is repeated until a visible slurry wave forms ahead of the roller, ensuring effective void filling and bonding.
Defective WBM layers exhibiting surface irregularities or contamination must be scarified fully, reshaped or replaced with fresh material, and compacted again following the code requirements. The rectification area should cover at least 10 m². Depressions must not be filled merely with screenings or binding material. Prior to laying WBM over existing surfaces, scarification and remedial measures for weak spots are mandated.
Maintenance includes periodic pothole patching, elimination of ruts and depressions, surface blinding by spreading fine aggregates, and surface renewal when deterioration is significant. When constructing WBM over bituminous layers, removing the existing bitumen or cutting grooves is advised to ensure proper bonding and drainage, thereby preventing early failures.
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