Spalled areas on concrete side walls are normally caused by water penetration through movement cracks, causing the rebar to rust, expand and spall the concrete from the existing surface. Once the process has started, additional moisture trapped behind spalled areas goes through a freeze-thaw cycle speeding up the process. Eventually the rebar can rust through and could reduce the structural integrity of the bin walls.
Also spalling can be caused by a chemical reaction, due to chemicals in the concrete mix during the construction process causing the rebar to rust.
To repair spalled areas, all loose and delaminated concrete needs to be removed and cleaned prior to priming of the exposed rebar. Spalled areas are then handpacked with a cemetious grout and floated out smooth with the existing concrete surface.