Risk of chloride-induced corrosion of steel in SF concrete exposed to a chloride-bearing environment

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Date: Mar. 30, 2018
Publisher: Elsevier B.V.
Document Type: Abstract; Report
Length: 8,102 words
Lexile Measure: 1600L

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ABSTRACT

The present study concerns the resistance of silica fume (SF) concrete against chloride-induced corrosion, when SF concrete is built in a chloride-bearing environment. Chloride transport and critical chloride threshold level were experimentally obtained, which were subsequently used for the Fick's 2nd law to calculate the corrosion-free life. As a result, it was found that SF concrete had lower chloride transport in terms of the apparent diffusion coefficient, due to a refinement of the pore structure, resulting from a further formation of C-S-H gel in the cement matrix. Simultaneously, the surface chloride for SF concrete had a slightly lower range, arising from the lower capacity to bind chlorides. However, SF mortar imposed the increased corrosion risk. The chloride threshold for SF mortar accounted for 0.45% by weight of binder, while OPC produced 0.96%. Despite the increased corrosiveness in SF concrete, SF concrete produced the longer corrosion-free life, compared to OPC. From the sensitivity analysis, a reduction of the parametric values on chloride transport in SF concrete could significantly increase the corrosion-free life. For example, the apparent diffusion coefficient for SF concrete was about 74% reduced compared to OPC concrete, and thus the time to corrosion was 270% increased.

Keywords:

Silica fume

Chloride

Corrosion

Diffusion

Sensitivity

1. Introduction

Silica fume (SF) has been preferred to admix in concrete mix, arising from its benefits of high early strength and low permeability. As the pozzolanic reaction of SF is very active to form the C-S-H gel, incorporating with precipitated Ca[(OH).sub.2], the distribution of pores is often shifted to smaller ones with the increased porosity more or less then to be resistive against permeation of external ions and molecules. Moreover, particles of SF are usually located at the interface between cement paste and aggregate [1], where is regarded as a source of weakness in concrete, leading to a further development of the concrete strength at an early age. These peculiarities of SF concrete could enhance the durability, in particular, increased resistance to sulfate attack [2], and to chloride-induced corrosion, although the alkalinity of the pore solution is reduced. Thus, SF seems to be an essential material to fabricate high durable concrete in a severe and harsh environment, despite its economic limitation. In particular, the high resistance to chloride-induced corrosion made it possible to use SF in concrete mix in a marine environment, arising from low permeability of chloride ions.

The resistance of SF concrete to chloride-induced corrosion may result from delayed chloride transport, which has been confirmed by a number of studies from laboratories [3] and in situ [4,5]. SF concrete has basically pores distributed to smaller ones (i.e. mainly gel pores), which would be otherwise governed by capillary pores. Thus, ionic transport could be lowered in SF concrete. Moreover, the C-S-H gel overwhelmingly formed in the cement matrix may increase the surface area of hydrated fractions, which could physically adsorb chloride ions then to remove from the pore solution. Substantially, the mobility of chlorides would be reduced in SF matrix, thereby increasing the lifespan...

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Source Citation   

Gale Document Number: GALE|A535612507