Title: Corrosion Performance of Prestressing Strands in Contact with Dissimilar Grouts

Author(s): Matthew O’Reilly, David Darwin, and JoAnn Browning

Publication: Materials Journal

Volume: 112

Issue: 4

Appears on pages(s): 491-500

Keywords: chlorides; corrosion; grout; macrocell; prestressing strands

DOI: 10.14359/51687751

Date: 7/1/2015

Abstract:
Anti-bleed grouts are often used to fill voids in post-tensioning ducts that result from bleeding and shrinkage of older portland cement grouts. This repair, however, exposes the strands to environmental differences from dissimilar grouts, differences that may cause rapid corrosion. Portland-cement grout, gypsum grout, and four commercially available prepackaged grouts were analyzed to determine the chemical composition of the resulting pore solutions and tested to determine the potential for accelerated corrosion. Grouts and simulated pore solutions were paired to evaluate their potential to cause corrosion of, respectively, grout-encased and bare prestressing strands using the rapid macrocell test. Strands were also evaluated in simulated pore solutions containing chlorides and in deionized water. Unprotected prestressing strands can exhibit rapid corrosion. Gypsum grout, with its low pH and high sulfate content, will cause accelerated corrosion of strands when used in conjunction with any of the other grouts tested. None of the prepackaged grouts resulted in significant corrosion when used in conjunction with portland-cement grout. The highest corrosion measured for a prepackaged grout occurred for the grout with the highest pore solution sulfate content.