Why is the use of granular sub-base in concrete carriageways not preferred?

Granular Sub-Base (GSB) is preferred in Concrete carriageways. GSB is a good filter media. GSB being granular in nature allows the ground water (raised due to high water table/ capillary action) to flow in lateral direction rather then upward direction. Hence, in this way it prevents the damage to Concrete carriageway/ pavement and enhances the Life span of Carriageway. But a layer of Dry Lean Rolled Concrete (DLC) is laid between GSB & Concrete Carriageway. DLC has a compressive strength (Cubes) of 10 N/mm2

 

 

• Sub bases are permeable and hence water can seep through them easily. 

The soil particles get pumped out through the joints on the application of traffic loads. This results in the creation of voids underneath the pavement structure. This leads to the weakening of the concrete surface and it can crack easily upon intense traffic loads.

• Instead if lean concrete is used for carriageways it greatly increases the strength of the roads and the load carrying capacity of the roads is increased
• Sub-bases implementation requires a lot of workmanship which can lead to an un-uniform distribution of the sub-base. This can lead to the cracking of the carriageway when there is severe traffic loading

Use of granular sub base is not preferred in concrete carriage ways because voids in the material. Whenever traffic load will press the sub base, fine particles will be faded out and there will be a space created which will crack it. Ultimately when sub base will crack, then concrete layer will not survive so long and it will be damaged.