Garden building diagnostic systems for sustainable preservation

A garden building located in Torino, 25 VERDE, designed by the architect Luciano Pia is object of a monitoring diagnostic campaign, started in 2016 and still in progress, for ensuring a long-lasting sustainable preservation. The residential complex of sixty-three apartments conceived as a habitable forest in which almost 200 trees cut down the fine dust caused by cars, is characterized by irregularly shaped terraces, supported by weathering steel tree-like structures. The weathering steels or high-strength low alloy steels have a unique interesting characteristic: they corrode under proper environmental conditions, forming a compact and tightly adherent oxide barrier that seals out the atmosphere and retards further corrosion. Dry and wet cycles create a protecting patina layer, meanwhile the constant presence of humidity and of aggressive gaseous pollutants (SO2, NOx, etc) in the atmosphere degrades the properties of the layer. The diagnostic intervention is centered in the monitoring of the weathering steel structures by means of in situ electrochemical techniques, as Electrochemical Impedance Spectroscopy (EIS). The experimental data confirm that the high sensitivity and low invasiveness of EIS makes it a powerful technique for corrosion assessment of metallic structures exposed outdoor.