How Roads are made ? : From Subgrade to Wearing Course (How We Build Durable Roads)

Delivering long-lasting roads isn’t just about hot asphalt on a cold morning. It’s a tightly controlled sequence—from subgrade proofing to final rolling—where moisture, temperature, layer thickness and joint control decide how your pavement performs for years. Below is a clear, contractor-level walkthrough based on a method statement covering subgrade, granular sub-base, asphalt base, and binder/wearing courses.

Scope at a Glance

This workflow prepares the subgrade, places a granular sub-base, then paves the asphalt base and the binder/wearing courses—all to specified lines, levels, and tolerances. It includes material specs, plant, temperature windows, compaction targets, and site QA. 

1) Subgrade: Line, Level, and CBR Checks

• Bring formation to design lines/grades per AFC drawings; replace weak soils (A-6/A-7 with CBR <30%) with approved fill to 600 mm depth in 150 mm layers. This ensures bearing capacity and uniform support before any granular layer goes down. 

2) Granular Sub-Base: Moisture, Thickness & Density

• Place as a uniform mixture—no segregation—spread by grader to ≤200 mm loose per layer, shape, water, and compact.
• Moisture content at compaction: ±2% of OMC.
• Achieve ≥95% MDD (BS 1377 Part 4); finish closed and stable, free of ridges/cracks or movement under plant. 

3) Asphalt Base Course: Temperature & Paver Control

• Prepare/clean the surface; where required, prime and allow it to cure sufficiently.
• Deliver mix so the paver runs continuously; mix temp ≥120 °C and ≤163 °C before dumping.
• Use an automatic paver to strike true crossfall/crown and uniform texture; rolling starts as soon as the mat bears the roller without shoving/tearing.
• Offset longitudinal joints by 150–300 mm between successive layers; manage string-lines and 10 m control points to maintain grade/line. 

4) Binder & Wearing Course: Finish and Joint Quality

• Tack coat, sweep clean, and pave within the same temperature window (120–163 °C).
• Stagger longitudinal joints relative to underlying layers; locate final joints at lane centers or lane edges as detailed.
• For cold transverse joints, cut back to sound vertical face across full depth, place fresh mix, and ensure straight-edge tolerance (e.g., 2 mm over 3 m across the joint). 

5) Rolling & Compaction: Sequence and Uniformity

• Breakdown rolling with steel rollers, followed by pneumatic-tire rolling, then finish rolling with steel rollers—at speeds slow enough to avoid displacement.
• Keep drums moistened to prevent pick-up; alternate lengths on passes; continue rolling until specified density is reached without inducing cracks. Defective/contaminated areas are removed and replaced. 

Materials & Plant

• Materials: granular sub-base, asphalt base, binder & wearing course, prime/tack coats, water—subject to Engineer approval.
• Plant: grader, automatic paver, steel & pneumatic rollers, brooms/power brooms, level, air compressor, hand tools. 

Quality Control, Inspection & Records

• Notify the Engineer before starting; after each sub-activity, notify prior to the next.
• Maintain daily records of progress and tests (density, temperatures, thickness checks). This closes the loop between design intent and field delivery. 

Health, Safety & Environment

• Use appropriate PPE and safe systems of work around hot bitumen, moving plant, and traffic interfaces; maintain housekeeping and dust control on granular works.