Effect of sewage sludge on passivation and chloride-induced depassivation of reinforcing steels in cement extracts

Abstract

This study systematically investigated the electrochemical and natural passivation abilities, as well as the chloride-induced corrosion behavior of low-carbon (LC) steel and 304 stainless steel (SS) in extracts from cement mixed with DSS, and incinerated sewage sludge ash at 650°C (ISSA650) and 850°C (ISSA850). The amino acids introduced by DSS could form an adsorption film on the steel surface. Although the amino acids impede the electrochemical passivation of both steels, they promote the natural passivation process of LC steel. The adsorption of silica-aluminum phases, significantly increased by ISSA650 and ISSA850 (especially the latter), acts as a physical barrier against chloride penetration, enhancing the pitting resistance of LC steel. In contrast, their influence on the pitting resistance of 304 SS is minimal due to its lower susceptibility to chloride-induced pitting. Based on these findings, the inhibition mechanisms of both steels were proposed, which may provide guidance for the design of highly durable reinforced concrete structures in marine environments.