i worked in the old tower when the cancer was treated and painted. I worked on the new tower project. I'm only going by what the engineers told me.
From an architecture site:
Poor workmanship during construction, low concrete cover to reinforcement, ingress of carbon dioxide to the rebar level causing corrosion due to concrete carbonation, or ingress of chloride into the concrete causing reinforcement corrosion are some of the causes of concrete cancer, indicated initially by concrete spalling and cracking.
Note the mention of CO2.