The effects of the reaction between concrete and aluminium were specially visible in slabs’ joists and consist in the loss of resistance and porosity of the concrete, resulting in endangering the building’s stability..
This reaction is due to High Alumina Cement which was used to produce joists as it dried faster than usual cements. The applying process was faster and the final resistance was higher than normal cement’s.
This cement features a high concentration of aluminium oxide, which causes chemical changes when interacting with certain agents, thus modifying its properties. When exposed to high temperatures and humidity, the structure of this cement changes from hexagonal to cubical.
Consequently, cement will reduce in its volume and will feature less density and more pores, will lose mechanical resistance and humidity will penetrate causing oxidation of the joist frame.
The agents involved in the reaction between aluminium and cement are atmospherical, therefore this issue only affected specific areas where these agents could be singled out, for instance these agents might have been found in proximity to the sea or a factory releasing gases which contain them.
In Spain, this cement was vastly used between 1950’s and 70’s during its construction boom years.