Abstract
The pore fluid within many concretes is highly alkaline and rich in reduced sulfur species, but the influence of such alkaline-sulfide solutions on the surface film formed on steel reinforcement is poorly understood. This study investigates the critical role of HS− in defining mild steel passivation chemistry. The surface film formed on the steel in alkaline-sulfide solutions contains Fe(OH)2 and Fe–S complexes, and the critical chloride concentration to induce corrosion increases at high sulfide concentration. However, this behavior is dependent on the duration of exposure of the steel to the electrolyte, and the nature of the sulfidic surface layer.
Highlights
As part of the global move toward reducing CO2 emissions from Portland cement (PC) production, and to produce highly durable concretes for demanding applications, PC is increasingly being substituted with ground-granulated blast furnace slag, a by-product of the ironmaking process
In the case of mild steel immersed in alkaline solutions without HS- (Fig. 1a), four anodic current peaks were observed on increasing the potential from - 1.20 V toward Ek,a, at approximately - 0.94 V, - 0.89 V (Peak II), - 0.72 V (Peak III) and - 0.67 V (Peak III’), and on reversing the potential, cathodic current peaks were observed at about - 0.96 V, - 1.05 V and - 1.14 V [10]
Based on the Open-circuit potential (OCP) and Rp of mild steel exposed to alkaline solutions containing sulfide (Fig. 3a, b), in conjunction with the guidance of ASTM C876-15 [55] and recommendations of other authors [56, 57], it may appear an increase in the HS- concentration in the electrolyte leads to an increased susceptibility of the steel to chloride-induced corrosion
Summary
As part of the global move toward reducing CO2 emissions from Portland cement (PC) production, and to produce highly durable concretes for demanding (e.g., marine) applications, PC is increasingly being substituted with ground-granulated blast furnace slag, a by-product of the ironmaking process. Based on the above discussion, it is important to highlight that for sulfide-containing electrolytes and those representing the pore solution of AAS, the original composition of the steel surface can only be determined using the anodic response of the first scan in a cyclic voltammetry test, as the chemistry of the electrolyte solution is altered significantly during the reverse cathodic sweep.
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