Über Concrete is a special type of super concrete originally designed by the ancient society known as the Da'at Yichud to build structures as hard as steel.
According to Anya Oliwa, Über Concrete is the essential building block of the Nazi Regime, being based on ancient Da'at Yichud technology with near-perfect structure. However, Set Roth's sabotage of the producing formula causes the concrete to quickly deteriorate over time and develop mold. Said mold also causes a severe allergic reaction in some people, as evidenced by several sick guards in Eisenwald Prison. Though some realize that something is amiss with the material, most citizens just shrug it off, believing it's just a coincidence, or blame it on "unhealthy living" in large cities such as Berlin.
Wolfenstein: The New Order
The mold on the concrete eventually led to the discovery of Set Roth in Camp Belica who was tampering with the formula of the concrete. The substance that causes the mold to develop was from the use of an altered limestone that exists only in Northern Croatia.
This discovery led to the Kreisau Circle to send B.J. Blazkowicz to Camp Belica in order to find Set Roth and break him out of the camp. This would supply them with an advantage they would need in order to launch an all out counter offensive against the Nazis.
In the mission to find Set Roth; it is therefore shown that the substance is produced in Camp Belica where they also mine the limestone necessary for its production.
Wolfenstein: The New Colossus
In 1961, Set Roth's sabotage of the formula of Über Concrete bears true fruit since the majority of Nazis's structure built by Uber Concrete has now begun to break down causing major damage and the Nazis are unable to figure out why.