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

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 granular sub-base is not preferred in concrete carriageways: > 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.