Corrosion Sensitivity of Concrete Mix Designs

About the report:

This study compared the durability of concrete mixtures containing supplementary cementitious materials (SCMs) by evaluating the permeability, absorption, and corrosion resistance of seven mix designs and two types of reinforcement.

Permeability and alkalinity are contributing factors to the durability of portland cement concrete and can strongly influence the service life and corrosion resistance of the embedded steel. In  reinforced concrete systems, the ingress of chloride ions increases the probability of corrosion of the reinforcing steel. Reducing the permeability of concrete enhances its durability by hindering the ingress of chloride ions from reaching the embedded steel surface and initiating corrosion. SCMs such as Class F fly ash, silica fume, and slag cement are widely used in concrete in an effort to reduce permeability. In addition, the alkaline environment of concrete enables the formation of a passive film on the surface of the steel. As long as this protective environment is maintained, the corrosion rate of the reinforcing bar will be insignificant for the majority of applications.

The results of this study indicated that the use of SCMs can reduce the permeability and absorption of the concrete, leading to more durable structures than those with plain concretes; therefore, their continued use in structures by the Virginia Department of Transportation is recommended. However, different SCMs have varying levels of durability, and the agency should consider this information when selecting SCMs for specific applications.

The absorption test results in this study provided a reasonable correlation with the corrosion test results. Therefore, the absorption test should be more closely investigated as a means of evaluating the corrosion protection provided by SCMs. This study also demonstrated that the corrosion-resistant reinforcement plays the most vital role in minimizing corrosion. SCMs provide durable concretes and in combination with the corrosion-resistant reinforcement ensure reinforced concrete structures with longer service lives.

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