Rebar strengthening in concrete

[Plainsboro]

I have a roof where from some areas (say 1% of total roof)concrete has spalled off and rebars are also rusted considerably. I can recommend various ways to patch up concerete but what about section loss of rebars. How to improve or bring at par with origianl cross-sectional area.

 

[SperlingPE]

The first thing to consider is how the rebar got to the state that they are in. Control the corrosion problem first. Make sure that your proposed fix does not cause different problems with corrosion.

Cut slots in concrete next to bars with section loss. Make slots long enough to develop new bars (as well as long enough to resist bending load). Epoxy bars in place or use some proprietary concrete appropriate for your application. Take care that new concrete will bond with old concrete (bonding agent may be required). Safely removing the concrete and cleaning the concrete are very important to this process. This process is manpower intensive.

Alternative to replacing rebar is adding frp or cfrp to your section. This is an expensive product, so it is not always a good alternative.