Document Type

Working Paper

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This item is available under a Creative Commons License for non-commercial use only

Abstract

Corrosion inhibitors as cement additions consist of powders or solutions that are added to concrete when mixed to prevent or delay corrosion. This paper presents an early-age evaluation of a new corrosion inhibitor, namely ELOTEX®COPRA900 following a corrosion and durability study on concrete samples with different cementitious materials.

A comparison of the corrosion inhibition properties of ELOTEX®COPRA900 against a well known and established corrosion inhibitor on the market, namely Calcium Nitrite and a control with no corrosion inhibitor product. Calcium Nitrite works by increasing the threshold of chlorides required for corrosion to begin. ELOTEX®COPRA900 on the other hand surrounds the embedded reinforcement with a secondary protective layer that is activated when the passive oxide layer also surrounding the reinforcement breaks down due to the initiation of the chloride corrosion mechanism. The aim of this project is to evaluate ELOTEX®COPRA900 in concrete mixes exposed to accelerated corrosion conditions including CEM I, PFA and GGBS cements.

The results from this experimental programme have demonstrated that ELOTEX®COPRA900 is an effective corrosion inhibitor. The results have shown, in every case, that concrete containing ELOTEX®COPRA900 are less penetrable to chlorides than those without. The addition of ELOTEX®COPRA900 has been found to alter the pore structure so it becomes discontinuous and a capillary blocking effect occurs. In the case of those concretes containing PFA and GGBS, it was found that ELOTEX®COPRA900 made no significant improvement to the corrosion and durability performance.

However, one noticeable effect of the inclusion of ELOTEX®COPRA900 in the concrete mix is the consistent reduction in the compression strength. This has found to be due to the hydrophobic layer that forms on the cement particles which affects the hydration and strength development. However, it is expected that this will only affect low strength concretes which are uncommon in challenging exposures. Also, the quantity of ELOTEX®COPRA900 used here (4% by mass of cement) would be seen as on the higher side of what would typically be recommended. Reducing the volume of ELOTEX®COPRA900 would therefore reduce these effects of loss in compressive strength.

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