Corrosion-inhibiting admixtures

The use of de-icing salts on concrete pavements has a deleterious effect on reinforced concrete. Many bridges and parking garages with cast-in-place concrete and reinforced steel develop cracks by allowing corrosive chemicals to react with the steel. In normal concrete, the water in the pores is highly alkaline and a protective iron oxide layer forms on the steel. This 

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A corrosion-inhibiting admixture is a chemical compound which, when added in small concentrations to concrete or mortar, effectively checks or retards corrosion. These admixtures can be grouped into three broad classes, anodic, cathodic and mixed, depending on whether they interfere with the corrosion reaction preferentially at the anodic or cathodic sites or whether both are involved [48]. Six types of mechanisms, viz. anodic (oxidizing passivators), anodic (non-oxidizing passivators), cathodic, precipitation... 

It is important to ensure that when using corrosion inhibitors with other conventional admixtures, they are added separately, at different times of the mix cycle. Corrosion-inhibiting admixtures which also accelerate the set of concrete may require the combination of a retarding admixture when ambient and mix temperatures exceed 35°C. In like manner, set-retarding corrosion inhibitors may require the addition of an accelerator to offset the retardation of early strength development (e.g. use of sodium nitrite in conjunction with sodium benzoate). 

Alternative Means of Protection In addition to the use of coated or alloy rebar, other means to mitigate corrosion of reinforcing steel in bridge structures consist of use of high-performance concrete, corrosion-inhibiting admixtures, or a... 

The economics of the use of calcium nitrite in corrosion-inhibiting admixtures with and without the addition of silica fume has been documented (23). The cost of a calcium nitrite protection system was estimated to be 5.40/m, and the cost increase to construct the deck using calcium nitrite inhibitor is 1.1%. It is estimated that the... 

Epoxy coatings cost approximately 4.7-5.3/l while antifoulants are more expensive at 11.8-21.1/1. Environmental regulations have led to decreased amount of chemicals released from industrial installations along waterways, especially corrosives such as chlorine. The materials of construction for some water structures have also changed. Piers and docks are no longer constructed with wood, but instead are constructed with steel-reinforced concrete. To improve the lifespan of the structure and prevent corrosion of reinforcing steel, fusion-bonded epoxy-coated reinforcement or corrosion-inhibiting admixtures are sometimes utilized in the concrete mix. 

NG Thompson, DR Lankard, M Yunovich, Proceedings for Evaluation of Corrosion-Inhibiting Admixtures for Structural Concrete, NCHRP Final Report, NCHRP Project 10-45, June 2000. 

S. A. Civjana, J. M. LaFave, J. Trybulski, D. Lovett, J. Lima, and D. W. Pfeifer, Effectiveness of corrosion inhibiting admixture combinations in structural concrete, in Journal of Cement Concrete Composites, Vol. 27, 2005, pp. 688-703. 

At this point the author would consider any use of the proven corrosion inhibiting admixtures for new construction to be an effective corrosion prevention measure if backed up with proper assessment and whole life costing. However, any application of inhibitors for repair of existing structures should be done on a trial basis with proper long-term monitoring of the treatment. 

Other proprietary corrosion inhibiting admixtures, mainly amine based, are also available although there is much discussion about longevity and effectiveness. Some of these issues are covered in Elsener (2001). As an additive to the concrete mix, inhibitors can be used along side other protective measures such as coated reinforcement. 

Miscellaneous admixtures Those other than what have already been described and are known to impart many benefits to concrete. Examples are latexes, corrosion inhibiting admixtures, alkali-aggregate expansion reducing admixtures, pigments, pumping aids, shotcreting admixtures, etc. 

Corrosion-inhibiting admixtures in conjunction with polymer-modified cementitious coatings applied to the rebar... 

Corrosion inhibitors. Corrosion-inhibiting admixtures are essentially designed to improve the performance of good-quality reinforced concrete. It has been emphasized that the function of such admixtures is not to make good concrete out of poor quality concrete. Adherence to this important principle is important in order to avoid unrealistic performance expectations for corrosion inhibitors in concrete. 

An important consideration for any corrosion-inhibiting admixture is its effects on the properties of concrete, such as workability, curing time, and strength. Many mechanistic details of commercial rebar corrosion inhibitors have remained relatively obscure because of the proprietary nature of their formulations. 

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