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For concrete carriageway, which type of subbase is better, granular subbase or lean concrete (cement-bound material)?

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Subbase serves the following functions in a concrete pavement:

(i) Aid in spreading load of road traffic.
(ii) Prevent pumping of fines from subgrade.
(iii)Protect the subgrade from frost.
(iv) Improve drainage of the pavement structure so that the pavement structure is mostly dry with minimum moisture.

Cement-treated bases are easy to construct and provide a stronger and more erosion-resistant platform for the concrete slab when compared with granular subbase. They are normally used for medium to high traffic loads. However, tensile stresses arising from temperature curling would be significantly increased by the presence of lean concrete subbase as compared to granular subbase. Moreover, there is an increase in frictional resistance between concrete slab and subbase.

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Granular subbase is susceptible to erosion and it retains moisture for long periods. They are normally used only for roads with low to medium traffic loads.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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