The number of prestressed concrete bridge structures utilizing high strength 7-wire strand (black strand) has increased steadily since the 1970s. The prestressing strand can be used in both the pre-tensioned and post-tensioned (PT) structures. Two years ago, the University of Texas completed a study where they evaluated various types of prestressing to determine their corrosion-resistance, including black strand as a control. The study concluded that epoxy coted strand performed somewhat better then stainless-clad and stainless steel for both corrosion resistance as well as mechanical properties. Despite these good results on epoxy coated strands, there are number of practical issues for their use in field, and owners are reluctant to adopt this product at present.
For post-tensioned structures, the stressed strands are enclosed in plastic or galvanized ducts and the ducts are filled with cementations grout to provide a barrier system to the enclosed strands. Unfortunately, a number of bridges have still had corrosion issues due to bleed water from the grout being collected at higher end anchorage areas, among other problems including issues with construction, quality control, and environmental concerns. Hence to avoid the inherent deficiency in the cementations grouts, it is desirable to study feasibility of alternate metallic 7-wire strands including epoxy-coated, copper and stainless clad, stainless steel, and other types of alloys to determine their efficacy in preventing corrosion and their cost effectiveness. This study is intended to focus only on metallic alloyed/clad strands, and not fiber-reinforced polymer compositions.
Expected Phase I Outcomes:
The objective of this phase is to identify alternatives to conventional high-strength 7-wire strand (black strand) for prestressed concrete bridges. The outcome expected from Phase I is the identification of suitable products which may meet required mechanical and physical properties for their use in post-tensioned bridges with regard to overall improved corrosion resistance and performance, and may be economically manufactured.
Expected Phase II Outcomes:
The Phase 2 study will select one or more strand products from Phase I and will perform a detailed evaluation on large scale stressed concrete bridge members for their constructability and long term corrosion performance. Phase 2 will result in the identification of the material/ products that provide high corrosion resistance, perform well in the field, and can be economically manufactured.