Dude, what you call the 'concrete base' is actually what they call the pavement layer in Civil Engineering. In this case, this is a rigid type of pavement. We also have flexible, semi rigid and composite types.
In Dar's BRT, they happened to choose to make the BRT lanes pavement rigid while the normal lanes were made flexible.
Now, the type of pavement does not determine whether a lane is a BRT lane or not. They could as well have made the Normal lanes to be rigid and BRT flexible or both rigid or both flexible. Claiming that a BRT lane has to have a rigid type pavement because the Dar BRT has rigid type pavement is as absurd as claiming all BRT buses must be blue in colour because Dar's BRT buses are blue in colour.
Now you see why I said you're talking about things you don't understand? I hope you do.