Chapter 2. Accomplishments

• The preferred primary corrosion-protection systems in many states has been fusion-bonded epoxy coated rebars (ECR), which have been used in approximately 20,000 reinforced concrete bridge decks. This rebar has performed very well in alleviating the problem of corrosion-induced deteriorations of concrete bridge decks. It is estimated that its use in the last 25 years has saved the taxpayers billions of dollars so far.
  
  With continuing improvements in the American Association of State Highway and Transportation Officials (AASHTO) and American Society for Testing and Materials (ASTM) specifications for ECR, this corrosion system will become even better. The improvements involved all possible aspects of the fabrication of ECR, including certification of coating plants, proper storage of coating powder at the plants, restriction on surface imperfections on the bars, removal of dust and salt from the surface of the bars prior to coating, and better quality control of thickness, continuity, flexibility, adhesion, etc. In addition, requirements related to job-site storage and handling of the coated bars have also been established. All of these will result in better ECR and more durable new concrete structures. Ongoing efforts to identify more effective organic coatings will also lead to more corrosion-resistant steel bars in the future.
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• To provide even longer service life to the concrete decks; G years or longer— without any need to repair corrosion-induced concrete damage, a number of alloys and cladding have been developed for rebars. Most notable are solid stainless steel 316 rebars and stainless steel clad black bars, which have performed exceedingly well in accelerated screening corrosion tests. Both of these two new alternative reinforcing bars have the potential to provide an excellent corrosion protection system, albeit at a higher initial cost.
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• The combined use of ECR and a corrosion inhibiting admixture, such as calcium nitrite, could serve as a very good corrosion protection system. However, the stability of this inhibitor is still under study. In addition, research efforts are under way to identify new inhibitors that are more effective than calcium nitrite.
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• The combination of high temperature (38° C) and an intermediate level of humidity or moisture (75 percent) have been identified as environmental conditions that lead to high corrosion rates for steel in concrete. It was found that the use of a low water-cement ratio, incorporation of mineral admixture and proper selection of cement type and aggregates contribute significantly to producing low-permeability concretes.
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• For the protection of high-strength, seven-wire strands encased in ducts, mix designs for corrosion-resistant grout for filling the ducts have been developed. In addition, an accelerated corrosion test method has been developed for evaluating new grout mixes. These developments have become the basis of a new specification to be published by the Post-Tensioning Institute (PTI) in 1998.
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• Prompted by the recent sudden collapse of two post-tensioned bridges in the United Kingdom and one in Belgium, several different nondestructive inspection techniques were carefully evaluated to identify those that may be suitable for detecting voids in post-tensioned ducts. From these, the impact-echo technique was selected for improvement; then, it was successfully evaluated in the field. The equipment for this technique is now commercially available. Further research is under way to develop a complementary magnetic-based, nondestructive technique for assessing section loss in the high strength steel strands in the ducts. It is anticipated that when used in combination, the impact-echo and the magnetic-based techniques will allow complete inspection of post-tensioned systems, reducing the likelihood of any sudden collapse of post-tensioned bridges in the United States.

For Rehabilitation of Existing Concrete Bridges

• Cooperative research with industry and states in the development of durable anodes, monitoring devices, installation techniques, etc. has led to application of impressed-current cathodic protection systems on bridge decks as a routine rehabilitation technique.
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• For cathodic protection of substructure members, especially those in a marine environment, two very promising sacrificial anode systems have been developed. Initiatives in the industry and in some states, in cooperation with FHWA, have led to further developments and identification of anodes suitable for impressed-current cathodic protection of inland concrete substructures.
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• Through extensive fundamental research and evaluation of cathodic protection systems that have been installed, significant advances have been made in the technology for cathodic protection of prestressed concrete components. Concerns about a loss of bond between the prestressing steel and concrete and possible hydrogen embrittlement (from overprotection of the prestressing steel) have been alleviated by the establishment of criteria for qualification of prestressed concrete bridge components for cathodic protection.