Rigid and flexible pavement design with stabilised base and sub base.
In modern highway engineering, both rigid and flexible pavement designs are increasingly incorporating stabilized base and sub-base layers as a substitute for conventional granular materials. Stabilization involves treating local or marginal materials with additives such as cement, lime, bitumen, fly ash, or proprietary chemical stabilizers to improve the strength, durability, and stiffness of pavement layers. This approach offers significant structural and economic benefits and is applicable to all categories of highways, including rural roads, urban streets, state highways, and national corridors.
- In flexible pavements, the conventional construction typically consists of a bituminous surface layer underlain by a base layer of Wet Mix Macadam (WMM) and a sub-base layer of Granular Subbase (GSB). With stabilized designs, these granular layers can be replaced by engineered materials such as a Cement Treated Base (CTB), Bitumen Stabilized Material (BSM), or Foamed Bitumen Base for the base layer, and a Cement Treated Subbase (CTSB) or Lime Treated Subbase (LTSB) for the sub-base layer. These stabilized alternatives offer higher structural capacity, improved resistance to rutting and moisture damage, and allow for a potential reduction in the thickness of the bituminous layers. However, to mitigate the risk of reflective cracking from cemented layers, it is often necessary to introduce an intermediate crack relief layer, such as a Stress Absorbing Membrane Interlayer (SAMI).
- In rigid pavement construction, the typical layer composition includes a Plain Cement Concrete (PCC) slab placed over a Dry Lean Concrete (DLC) base and a GSB sub-base. These traditional layers can be effectively replaced by stabilized materials, where Cement Treated Base or Roller Compacted Concrete (RCC) can substitute DLC, and CTSB or LTSB can replace the GSB. The use of stabilized layers under concrete pavements results in a more uniform and stronger support system, improving load transfer and reducing the risk of cracking and pumping. Moreover, stabilized bases provide higher subgrade reaction values (k-values), which can lead to thinner concrete slabs without compromising performance.
In both pavement types, the adoption of stabilized layers contributes to enhanced construction speed, material efficiency, and long-term performance. This is particularly beneficial in regions with poor natural materials or where sourcing high-quality aggregates is cost-prohibitive. However, the design and implementation of these layers must adhere to the performance criteria specified in relevant standards such as IRC:37 for flexible pavements and IRC:58 for rigid pavements, including requirements for strength, durability, and environmental compatibility. Overall, the integration of stabilized base and sub-base layers represents a forward-looking and sustainable approach to highway design and construction.
