Corrosion of some metallic materials embedded in gypsum

Abstract

In the construction area, as well as in the restoration of old and historicalbuildings, different metallic materials are frequently in contact with gypsumplaster. Due to the high porosity of gypsum plaster, and particularly in highrelative humidity environments, the risk of corrosion exists. In the presentwork, carbon, galvanized and stainless steel, as well as copper, were embeddedin gypsum plaster (with varying water/gypsum ratios) and exposed to differentenvironmental conditions, and the corrosion rate was assessed by electrochemicaltechniques. Stainless steel showed very low corrosion rates, carbonand galvanized steel showed considerable corrosion rates, and copper showedmoderate corrosion rates. The higher the humidity, the higher the corrosionrate, independently of the water/gypsum ratio. A comparison with resultsobtained for the same materials embedded in mortar was performed. Exceptfor stainless steel, the corrosion rates obtained in gypsum are higher thanthose obtained in mortar, being this difference up to two orders of magnitude.The differences in the pH of both matrices explained the lower corrosion ratesmeasured in mortar.