Materials Performance

OCT 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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OCTOBER 2018 WWW.MATERIALSPERFORMANCE.COM 42 Increased Use of Alternatives to Steel Concrete Reinforcement The simple answer to addressing reinforcement corrosion issues in concrete is to replace steel with a less or noncorroding material. While alternative reinforcement is already available in the forms of stainless steel, galvanized steel, fiber reinforced polymer (FRP), or epoxy coated reinforcement, the cost is often much greater, the development of the reinforcement (load transfer) is different, or defects in the epoxy coating can accelerate corrosion propa- gation. Many technical advancements are ongoing with the use of synthetic fibers to create ductility in concrete by balancing the fiber elongation, bond, and tensile strength to that of the concrete binder commonly referred to as ECC (Engineered Cementitious Composite). With the proper balance of mate- rial properties, many very fine cracks occur that are held tightly together by the embedded fibers, resulting in an isotropic composite material. Many treatments are available for fine cracks such as elastomeric coatings, mem- branes, and hydrophobic sealers that can minimize the ingress of deleterious materials into the cracks. In addition, polymeric fibers can improve the fire resistance of concrete by melting to form escape channels for trapped water as it turns into steam. Conventional concrete is pretty good compared to other building materials at surviving floods, fires, hurricanes, tornados, tsu- namis, and other natural disasters, except for earthquakes. ECC can greatly improve the survivability of concrete in seismic events due to the ductility and crack stitching effects of the specialized fibers. Concrete develops its physical properties over long time periods as cement hydration occurs, so another evolution of ECC will be balancing of the fiber properties to the con- crete properties as the concrete matures (such as control of plastic and dry- ing shrinkage). The advent of 3D printing with concrete will also likely require fibers, but if conventional reinforcing steel is used the consistency and qual- ity of placement can be greatly enhanced through robotic placement, thereby reducing the corrosion risk. New Corrosion Inhibitors Corrosion inhibiting admixtures are added to concrete to increase the stabil- ity of the passivating layer on the reinforcing steel formed by the alkalinity of concrete. Current technologies include nitrites, amino alcohols, amine esters, and amine carboxylates and have been commercially available for several years. The development of concrete admixtures is a mixture of both art and science as many factors must be balanced to produce the required performance of the concrete. Research continues to develop new technolo- gies and materials to reduce corrosion of reinforcing steel. Geopolymer Embedment of ICCP Anodes in Concrete to Address Acidification Cathodic protection (CP) is the only rehabilitation technique that has been proven to stop corrosion in salt-contaminated bridge decks regardless of the chloride content of the concrete according to the U.S. FHWA (Federal High- way Administration). Impressed current CP (ICCP) has been successfully used for many years to address corrosion issues in reinforced concrete but suffers from the deterioration of anode embedment materials due to the acid formed during operation of the system. Geopolymer materials are alterna- tive inorganic binders that are resistant to acids and can have the appropri- ate physical characteristics for durability in concrete and tailored to the proper resistivity for satisfactory current distribution in ICCP. Research con- tinues to develop appropriate formulations for this application. New and Existing Infrastructure The American Society of Civil Engineers Report Card estimates a U.S.$4.6 trillion investment is required over the next 10 years just to return our

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