For spalling fix, it's far worthwhile to do away with all unsound concrete except reliable substrate is reached

https://deanlith562.wpsuo.com/structural-concrete-restoration-for-tilt-up-panels-common-repair-scenarios

For spalling restore, that is central to dispose of all unsound concrete except reliable substrate is reached, then refreshing steel to a defined time-honored sooner than employing coatings or patch substances.