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Reconstruction

In cases where a road has significantly deteriorated, periodic maintenance can involve reconstruction. This is a comprehensive process that involves the complete removal and replacement of the pavement’s surface, sub-base, and other structural components. Reconstruction aims to address severe structural issues and create a new, long-lasting road.

Methodology and process involved in the reconstruction procedure

Assess the existing pavement structures, noting the types, conditions, thickness, material types, and any visible distress or degradation of each layer.
  • Perform a plasticity index test on soil or aggregate samples to evaluate their plasticity characteristics, which influence workability and stability.
  • Test the aggregate crushing value (ACV) to assess the strength and durability of the aggregates used in the pavement mix.
  • Measure the flakiness index to determine the shape and texture of the aggregates, which affect the performance of the pavement.
  • Conduct the California Bearing Ratio (CBR) test to evaluate the load-bearing capacity of the subgrade or sub-base materials, informing the design of the new pavement structure
  • Analyse the gradation of aggregates to ensure that their particle size distribution complies with the specifications required for the pavement mix.

Complete a structural design of the pavement to determine the necessary layer thicknesses and material specifications, ensuring the pavement will support the anticipated traffic loads and environmental conditions.

Mobilize and set up the required machinery for reconstruction, ensuring all equipment is calibrated and operational.

Clearly mark and delineate the construction area to define work boundaries and ensure safety and efficiency throughout the reconstruction process.

This is typically done using a milling machine (also known as a cold planer) to remove the existing asphalt layer. In cases where the pavement is exceptionally thick or heavily deteriorated, a bulldozer may also be used to assist in material removal.

Excavation down to the subgrade follows. This is carried out using an excavator to remove the underlying materials, and dump trucks are used to haul the debris away from the site.

Regrading or replacing the subgrade is essential to ensure a stable foundation. A grader is used to level the surface, while a water tanker provides moisture conditioning to facilitate compaction. A padfoot roller is then used to achieve adequate subgrade compaction

Subgrade Requirements:

  • A minimum California Bearing Ratio (CBR) of 5% is recommended for subgrades intended to support traffic volumes classified as Traffic Classes T1 through T3.
  • For pavements designed to support higher traffic volumes – specifically Traffic Classes T4 and T5 – a minimum subgrade CBR of 12% is recommended.

Placing and compacting the sub-base layer is the next step. The material is delivered using dump trucks, spread and leveled with a grader, and then compacted using a smooth drum roller to form a stable intermediate layer.

Sub-base Requirements:

  • The sub-base material should achieve at least 95% of the Maximum Dry Density (MDD), with a maximum dry density no less than 30% of the standard reference.
  • The Plasticity Index (PI) of the sub-base material should not exceed 25%.
  • The 10% fines value of the sub-base material must fall within the specified limits to ensure adequate strength and durability.
  • The sand equivalent value of the aggregate fraction passing through a 4.75 mm sieve should be no less than 45%, based on sieve analysis.

Placing and compacting the base layer follows the same procedure as the sub-base. The process again involves dump trucks for material delivery, graders for leveling, and rollers for compaction.

Road Base Requirements:

  • The The Aggregate Crushing Value (ACV) should be no more than 25%, indicating the aggregate’s strength and durability. of the crushed aggregate road base should not exceed 6.
  • The Aggregate Crushing Value (ACV) should be no more than 25%, indicating the aggregate’s strength and durability.
  • The Flakiness Index of the crushed aggregate should not exceed 25%.
  • The weighted average loss of weight in the Magnesium Sulphate Soundness Test should not exceed 18%.
  • The California Bearing Ratio (CBR) of the crushed aggregate road base should be greater than 80%, demonstrating high load-bearing capacity.
  • The Sand Equivalent Value of the aggregate fraction passing through a 4.75 mm sieve should be no less than 45%.

The prime coat should be applied at a rate of 0.5 to 1.0 litres per square meter, adjusted based on the ambient temperature ranging from 25ºC to 45ºC during spraying.

The Asphaltic Concrete Binder Course (ACBC) 28 must comply with the standard specifications established through plant trial.

  • This compliance includes successful completion of testing for sieve analysis, bitumen content, and Marshall properties.
  • The rolling compaction pattern must be established and applied effectively thus, achieve a Marshall density of 95%.
  • The average thickness over any 100-meter length ≥ the required thickness. The minimum thickness at any point should be at least the required thickness ± 5 mm, as verified by coring.

The tack coat should be applied at a rate of 0.25 to 0.55 litres per square meter.

  • The Asphaltic Concrete Wearing Course (ACWC) 14 must comply with the standard specifications established through plant trial. This compliance includes successful completion of testing for sieve analysis, bitumen content, and Marshall properties.
  • The rolling compaction pattern must be established and applied effectively thus, achieve a Marshall density of 98%.
  • The average thickness over any 100-meter length ≥ the required thickness. The minimum thickness at any point should be at least the required thickness ± 5 mm, as verified by coring.
Apply temporary road marking for safety of road users. Then, apply Permanent road marking work shall be carried out after 72 hours.

The defect liability period for the project is either 6 or 12 months, depending on the project cost.