RCC column is structural member. It is also load bearing member of the structure. Its repair should be done with utmost care as load of the building portion is born by the column. If its strength is reduced by the crack below, safety factor of the building may be collapsed. Before starting repair of the crack, MS Steel provided in RCC column should be checked carefully whether there is any rusting in MS Steel.  

These cracks should be filled in with pressure grouting or ‘guniti’. The material for such grout can be APOXY or cement (with suitable admixture). APOXY can go into very thin cracks also as fine as 0.1 mm. Its strength and adhesion is also much more than that of cement. The ‘guniting’ process is mechanical process and it should be done through expert in this field. It is also advisable to consult an expert of RCC structure to repair the RCC column.

For more info on cracks, click on the link below:

How to Repair cracks