A lot of questions about steel bars corrosion in the reinforced concrete structures. There are a  lot of money spend worldwide to repair  the structures due to corrosion. The reason of corrosion is discussed in this book https://elreedyman.com/publications/  Steel  reinforced concrete structure assessment and repair of corrosion. There are two approaches in studying corrosion as by chemical reactions or electrical theories, I try to make a mix in this book,  as an engineers we need a solution at the end so it is important to understand this phenomena very well. The corrosion mainly happened due to chloride, carbonate or sulphate which is existing in the soil. There are a lot of equations can calculate the carbonation propagantion rate and the chloride dufision inside the concrete and to predict the time  of spalling  concrete cover can also be calculated as per the belowbook or the eBook Causes of corrosion and concrete deterioration

Before start to the repair you need to do an assessment first to define the root cause as per my statement “ Do not Jump to the Conclusion”. Clear example if the corrosion is due to chloride so it is required to know if the chloride attack from outside or from inside the concrete as for both there are an extreme repair solution as for instant if chloride is from outside if cost 1 USD from inside can cost 10-50 USD.

The corrosion start time is different from structure to another depending on the construction quality. In case of good quality control in construction the structure can leave to 60 years without start corrosion in normal conditions.

Pedicting the concrete structure life time can be calculation depending on many factors for the building design, cosntrsuction manitenance history and environmental conditions

There are a lot for protections solution are presented in the advanced materials books.  The method of protection depends on the structure location and the environmental condition and its nature of occupancy.

‘Do not Jump to The Conclusion’

If you have a protection or not and the assessment of the corrosion extension and the surrounding environmental conditions and the economic value of that repair, then  you need to start repair. Considering that if the repair cost around 75% of the new building as a rule of thumb go to the new building option.

The first question raise is this repair urgently required?  Or we can wait until we have a budget available?. This depends on the structure reliability which is function on the structure system and method of construction, code of design all together which is start of the structure integrity new approach.