ABSTRACT:

Two types of emerging technologies to mitigate corrosion in reinforced concrete structures were demonstrated at military installations in highly corrosive environments. The first technology consisted of surface-applied corrosion inhibitors, while the second was a surface-applied sacrificial cathodic protection coating. The corrosion inhibitor system consisted of (1) an ionic-anodic type of inorganic penetrating corrosion inhibitor, (2) an organic vapor phase penetrating corrosion inhibitor, and (3) a reactive silicone surface protection agent. The combined application of these three corrosion-inhibiting formulations provided a durable and multifunctional corrosion-inhibiting environment along with a reduction in water penetration rate. The sacrificial cathodic coating system consisted of an inorganic silicate vehicle containing zinc, aluminum, magnesium, and indium metal powders. The coating was applied to a reinforced concrete surface along with titanium mesh strips that were connected to the rebar to conduct cathodic current. Before and after measurements indicated that corrosion rates of the rebar were reduced by a factor of 3.5 for the penetrating corrosion inhibitor and 2.7 for the sacrificial cathodic protection coating. Water permeation rates were also significantly reduced. The results indicated that properly selected and applied penetrating corrosion inhibitors or sacrificial cathodic coating systems can be successfully used to extend the life of reinforced concrete structures by reducing corrosion rates.

INTRODUCTION:

Problem Statement The corrosion of steel rebar in reinforced concrete structures is a pervasive and expensive problem for the Department of Defense. The maintenance and repair costs for affected structures and equipment amounts to hundreds of millions of dollars each year, and the degradation negatively impacts military readiness and infrastructure safety 1. Despite the numerous technological advances in corrosion prevention and control in recent decades, innovative new methods are continually sought to address persistent corrosion problems for which straightforward solutions have not yet been developed. It is known that new properly constructed alkaline (pH 13) concrete cover of 2 inches will inhibit corrosion of the rebar. This alkalinity and its protection will decrease over time due to carbon dioxide (CO2) and other acidic materials in the environment penetrating into the concrete and dropping the pH below 11, at which point the natural corrosion inhibition is lost. Also, if air and water (moisture) are in contact with the rebar, corrosion will take place, as CO2 absorbed from the atmosphere decreases the pH (carbonation). Another main source of corrosion is from salt (chloride ions). These can originate from salt water and deicing materials penetrating the concrete and migrating to the rebar level where they accelerate corrosion. These corrosion products expand and cause the concrete to degrade and spall. Rebar Corrosion Protection Systems Used in This Project The first rebar corrosion protection system is a penetrating corrosion inhibitor system (PCIS). It is comprised of 3 basic surface applied chemical formulations: (1) an ionic-anodic type of penetrating inhibitor, (2) an organic vapor phase penetrating inhibitor and (3) a reactive surface protection agent. The PCIS can function at either or both of the anodic and cathodic mechanism sites applied to the surface of the surrounding material.

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