It seems to me very much (yet) theory only. From experience in actually building reinforced concrete structures (both bridges and tunnels) and following later

It seems to me very much (yet) theory only. From experience in actually building reinforced concrete structures (both bridges and tunnels) and following later checks/inspections the amount of dirt (be it smog, pollution, dust, spiderwebs, whatever) on a structure that has been built only a few years before is impressive and would probably make this kind of microcracks detection not feasible/ineffective, let alone via a camera (or a drone). Typically (talking of box girders where you could walk inside the bridge) you would normally check areas where you would suspect a (macro) crack to possibly develop by brushing with a hard brush the area and (not always, but it happened) pressure wash it.