Corrosion risk of bonded, post-tensioned concrete elements

Abstract

Corrosion protection for bonded, internal, posttensioning tendons (PTTs) can be effective. Within structural elements, PTTs can be well protected by a multilayer system that includes sound design of surface treatments; high-quality concrete; corrosion-resistant ducts; high-quality cementitious grout, coatings, and other internal barriers in the prestressing steel; and superior anchorage protection measures. Potential weaknesses exist in the protection system, however, when the concrete has high permeability or when the concrete is cracked. Additional weaknesses can occur when the posttensioning ducts are not adequately spliced and lack adequate impermeable concrete cover or when the portland cement grout contains voids, bleed water, or cracks. Lastly, the prestressing steel may be more susceptible to corrosion if not adequately protected or handled during construction. Over the past 2 decades, numerous countries reported damage and failure of individual tendons in transportation structures. A thorough research program, initiated at the Phil M. Ferguson Structural Engineering Laboratory, undertook 4 experimental research programs: 1) a study of high performance grouts with the goal of improving the corrosion protection of prestressing strands; 2) a long-term macrocell corrosion test series, initiated to investigate corrosion protection for PTTS to precast concrete segmental construction in which half of the macrocell lab specimens underwent internal examinations after 4-1/2 years and the other half after 8 years of exposure testing; 3) long-term beam corrosion tests that examined the effects of posttensioning and crack width on corrosion protection; and 4) a long-term column corrosion test series initiated to examine corrosion protection in vertical elements. This paper documents the results from the macrocell, beam, and column corrosion test series and recommends durability-design guidelines based on the overall research results.