Self-healing concrete by biological substrate 生物自我修復混凝土?

1) Mechanism機制 
As my understanding, the self-healing process by bio need water to activate. 
However, water seepage is one of the main cause of concrete defect. 
The mechanism of concrete spalling seem contradict with the mechanism of self-healing. 
If a crack noted at concrete, water apply it will case reinforcement corrosion. 
Negative impact of concrete spalling case by reinforcement corrosion is bigger than the benefit of self-healing of crack. 
However, if the product get negative bigger than benefit, it cannot be product in the market. 
 
There should be some wrong understanding of self-healing concrete or something important thing overlooked 
Any one can provide more information for the mechanism of self-healing concrete? 
Great Thanks 
2) Application cost in Hong Kong (e.g. unit rate)香港應用的價格3) Any project example about caption apply in Hong Kong construction? 香港應用例子