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Without doubt, active corrosion protection of prestressing steels by cement grout can be one of the most economic and durable solutions, if properly executed. Numerous other corrosion protection systems which fulfill requirements such as controllability and exchangeability are available. This state-of-the-art report, prepared by a task group and approved by fib Commission 9 Reinforcing and prestressing materials and systems, concentrates exclusively on factory applied corrosion protection that can be produced in controlled processes which should assure a better quality than corrosion protection applied on site. The report is addressed to designers and installers (executing persons) attempting to inform them about the various possibilities for industrially applied corrosion protection and to provide the necessary knowledge for their application.
Recognizing the burden that reinforcing steel corrosion imposes on natural resources, the Federal Highway Administration established Corrosion Protection for Concrete Bridges as one of the high-priority areas (HPAs) in its Structures Research Program. This report summarizes the progress made through research efforts conducted under these programs. The results presented cover (A) corrosion control in new concrete constructions (adequate concrete cover, quality concrete, rebar coatings, corrosion inhibiting admixtures, and corrosion protection of prestressed concrete bridge members) and (B) corrosion control for rehabilitation of existing concrete structures (conventional rehabilitation methods, cathodic protection, and electrochemical removal of chloride).
This is the final report in a study to demonstrate the feasibility of using cathodic protection (CP) on concrete bridge structures containing prestressed steel. The interim report, FHWA-RD-95-032, has more details on the installation of selected CP systems. Past laboratory and test yard studies had indicated that overprotection could result in the evolution of atomic hydrogen and the embrittlement of prestressing steel. Systems utilizing catalyzed titanium mesh, conductive rubber, and arc-sprayed zinc anodes were installed on prestressed pilings and girders of the Howard Frankland Bridge in Tampa, Florida; and systems using flame-sprayed zinc and conductive paint anodes were installed on the soffit of prestressed box beams of the Abbey Road and West 130th Street bridges near Cleveland, Ohio. For most of the components tested, CP was achieved safely and reliably without reaching conditions that could result in embrittlement of prestressed steel.
The use of cable-stayed bridges in medium- and long-span applications in the United States has increased significantly in the past ten years. Of paramount importance with this type of bridge is the protection of the stay cables from corrosive elements. An extensive survey, reported herein, showed a general concern over the adequacy of the corrosion protection of the most widely used current system. In this study, the popular two-barrier system (prestressing strand inside polyethylene sheath injected with portland cement grout) was examined experimentally. The effectiveness of the grout in providing secondary corrosion protection in the event of a cut or break in the external sheathing was a major focus of the experimental work.
In some countries durability problems with post-tensioning tendons have in the past led to fairly restrictive regulations. Improvements to execution procedures have been developed since, and new or improved prestressing systems have been proposed, too. This development was, of course, subject of discussions in fib Commission 9 Reinforcing and Prestressing Materials and Sytems and in IABSE Working Commission 3 Concrete Structures. It was decided to organise a workshop with the aim to review the different aspects of the problems encountered and to discuss solutions available today. Keynote speakers from various countries were invited to contribute. Their papers are published in this bulletin, grouped together under the following themes: Inventory and condition (6 papers) Investigation and repair (5 papers) Technical progress (4 papers) Strategies for improvement (6 papers) Supported by the international federation for structural concrete fib, and the international association for bridge and structural engineering IABSE, the workshop took place on 15-16 November 2001 at Ghent University, celebrating the 75th anniversary of the Magnel Laboratory for Concrete Research, whose director also chaired the Scientific Committee and edited the bulletin. It needs to be emphasised that in the bulletin invited experts present their individual views. Although not yet discussed in any of the association's working bodies, the highly topical contents of the bulletin is believed to be of general interest to fib's members and to document a starting point for future work in this field. Therefore, the Council of fib agreed to exceptionally publish these papers within fib's series of Bulletins.