GSB is a layer of well-graded granular material placed over the subgrade to provide structural support, distribute traffic loads, and improve drainage in flexible pavement construction.
GSB construction is covered under MoRTH Clause 305 in Section 300 (Earthwork and Subgrade Preparation).
GSB provides a stable base for upper layers, reduces stress on subgrade, prevents deformation, and ensures long-term pavement performance.
Crushed stone, gravel, or natural aggregates conforming to MoRTH gradation and quality specifications.
Usually 150–250 mm compacted thickness per layer, depending on design traffic and subgrade strength.
The subgrade must be well-compacted, leveled, free from soft spots, debris, and excess moisture.
Each layer should be compacted to 95% of maximum dry density (Proctor Test) or as per MoRTH specifications using rollers.
Motor graders for spreading, and vibratory or smooth steel rollers for compaction.
Tests include gradation, Proctor density, compaction, moisture content, and layer thickness verification.
Poor GSB can lead to settlement, pumping, rutting, reduced load distribution, and premature failure of the pavement structure.
CTGSB is a layer of crushed stone aggregate mechanically crushed and compacted over subgrade to provide higher strength and better interlock than conventional GSB.
CTGSB is specified under MoRTH Clause 306 in Section 300 (Granular Sub-base and Subgrade Layers).
CTGSB provides improved load-bearing capacity, better stability, reduced deformation, and increased interlocking of aggregates.
Crushed stone aggregates, stone dust, and fines, blended and compacted as per MoRTH grading requirements.
Usually 150–200 mm compacted thickness, depending on design traffic and subgrade conditions.
The subgrade must be uniform, well-compacted, free from loose soil, debris, or water logging.
Layers are compacted using vibratory rollers, sheepsfoot rollers, or pneumatic rollers to achieve required density.
Motor graders for spreading, stone crusher plants for preparation, and rollers for compaction.
Tests include aggregate gradation, Proctor density, layer thickness, compaction, and moisture content checks.
Segregation, poor compaction, uneven settlement, rutting, and reduced pavement life.
WMM is a base course of mechanically interlocked crushed aggregates bound with water and compacted to provide strength, stability, and a load-bearing platform for bituminous layers.
WMM is governed under MoRTH Clause 304 in Section 300 (Granular Base Layers).
Prime coat is a low-viscosity bituminous application on granular base layers to bind loose aggregates, seal the surface, and improve adhesion with the subsequent bituminous layer.
Prime coat is specified under MoRTH Clause 502 in Section 500 (Bituminous Treatments).
Cutback bitumen (RS-1, RS-2) or diluted bitumen emulsion, depending on surface conditions and MoRTH specifications.
It seals the base layer, improves adhesion for the next bituminous layer, and prevents dusting or loss of aggregates.
Tack coat is a thin bituminous emulsion layer applied between existing and new bituminous layers to ensure proper bonding and prevent slippage.
Tack coat is specified under MoRTH Clause 503 in Section 500 (Bituminous Treatments).
Bitumen emulsion (SS-1, SS-1h, or RS-1) applied at a controlled rate, depending on surface texture.
It ensures strong bonding between layers, prevents delamination, and improves structural performance of the pavement.
DBM is a bituminous base course of graded crushed aggregates and bitumen, laid and compacted to provide strength, durability, and load distribution in flexible pavements.
DBM is governed under MoRTH Clause 505 in Section 500 (Bituminous Macadam).
Crushed aggregates of specified grading and bitumen (VG-30, VG-40, or PMB as per MoRTH) blended and laid at designed bitumen content.
DBM provides a strong, dense, and interlocked base to support surfacing layers, distribute traffic loads, and resist deformation and cracking.
Tests include gradation, bitumen content, Marshall stability, compaction, density, and layer thickness as per MoRTH guidelines.
BC is the surfacing layer of flexible pavement, composed of graded aggregates, filler, and bitumen, laid and compacted to provide smoothness, skid resistance, and durability.
BC is specified under MoRTH Clause 507 in Section 500 (Bituminous Concrete). Variants include standard BC and BC with modifiers.
Crushed aggregates, mineral filler, and bitumen (VG-30, VG-40, or PMB), proportioned as per MoRTH mix design.
BC provides a durable, skid-resistant, and smooth wearing surface, protecting underlying layers from water ingress and traffic stresses.
Tests include aggregate gradation, bitumen content, compaction, density, smoothness, and Marshall stability as per MoRTH standards.
It is a modified bituminous concrete where shredded waste plastic is mixed with hot bitumen to enhance strength, rutting resistance, and durability of the pavement.
This method follows MoRTH guidelines for Bituminous Concrete with modifiers (clause 507) and the latest circulars on waste plastic utilization.
It improves binder adhesion, reduces rutting, enhances water resistance, and promotes sustainable recycling of plastic waste.
Polyethylene (PE), polypropylene (PP), and polystyrene (PS) are commonly used, shredded into small sizes (2–5 mm) before mixing with bitumen.
Tests include Marshall stability, flow, VFB, density, bitumen content, plastic content verification, and skid resistance as per MoRTH 2025 specifications.
