Influence of cementitious binder on chloride removal under electrochemical treatment in concrete

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Date: Feb. 1, 2016
Publisher: Elsevier B.V.
Document Type: Abstract; Report
Length: 5,463 words
Lexile Measure: 1610L

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ABSTRACT

The present study concerns electrochemical treatment to extract chloride ions and to repassivate the corroded steel in chloride-contaminated concrete. As binder, ordinary Portland cement (OPC), ground granulated blast furnace slag (GGBS) and pulverised fuel ash (PFA) were used to produce different concrete mixes: OPC, GGBS and ternary mix containing the three binders, respectively. After 56 days of curing, a DC was supplied to the concrete specimens, ranging 250, 500 and 750 mA/[m.sup.2] for 4 weeks. Then, the corrosion rate was measured by the anodic polarisation. In fact, an increase in the current density applied to the specimens resulted in a decrease in the corrosion rate, imposing a reduction of the corrosiveness of steel in concrete. For a change in the chloride profile, a removal of chlorides at the depth of the steel was more significant in GGBS and ternary mixes, presumably due to a release of adsorbed chlorides on the hydration surface into free, which was further removed under electric charge. However, all chlorides could not be removed by the immobility of chlorides chemically bound into chloroaluminate and chloroferrite hydrates; a mostly half of chlorides in cast were, in fact, present even after the treatment.

Keywords:

Chloride

Corrosion

Electrochemical treatment

Binder

1. Introduction

Electrochemical chloride extraction method was developed in the 1970's for the repair of reinforced concrete structures subject to chloride-induced corrosion [1]. Its principle is to apply a high voltage DC current between the steel reinforcement and an external anode in order to force chloride ions away from the steel. The anode is usually a titanium mesh that is placed on the outside of the concrete surface and is in contact with an electrolyte solution. The current density used in chloride extraction typically exceeded 1-2A/[m.sup.2] and the duration of application varies from 6 to 10 weeks. Due to the high current density applied to concrete, the electrochemical chloride extraction method more or less achieved a chloride removal at the depth of the steel and thus mitigating corrosion of steel, depending on the current density and voltage [2], for example, found that chloride-induced corrosion was arrested after applying a current of 8.37A/[m.sup.2] for 8 weeks, resulting in the removal of chloride ions at the steel-concrete interface. Orellan et al. [3] reported a significant removal of chloride at the steel-concrete interface with 50% extraction of chloride in the cover concrete after 7 weeks treatment.

However, the high current density in electrochemical treatments may reduce the bond strength between the steel and concrete. A reduction of 30-60% in bond strength has been reported in the majority of previous studies [4-6]. Moreover, the high current densities used appeared to be unrealistic to apply in in-situ. More currently, Buenfeld and Broomfield [7] showed a relatively lower reduction in bond strength compared to previous studies, ranging from 11% to 25%, when the current density applied was in the range of 100-750 mA/[m.sup.2]; in fact, the reduced bond strength was recovered in 24 h. Thus, it can be advisable to optimise the current density for...

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Source Citation   

Gale Document Number: GALE|A444093541