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Investigation of the Internal Stresses Caused by Delayed Ettringite Formation in Concrete

Delayed ettringite formation (DEF) in concrete has been identified in recent years as a significant cause of deterioration in some of the reinforced concrete infrastructure in Texas. This report is part of a research project, Texas Department of Transportation (TxDOT) project 5218, to investigate the possible long-term structural and durability related effects of DEF in such structures. The focus of this particular report is the determination of the internal stresses caused by DEF which at this point in time are not known. The research presented here began by first looking at past and recent research involving concrete deterioration due to alkali-silica reaction (ASR) and discussing the results of a comparative study between DEF and ASR affected concrete with different dosages of steel fibers to provide restraint. The study then went on to directly study the stresses caused by DEF in a new testing methodology that was developed using a Hoek triaxial load cell to provide a direct measurement of the confining stress necessary to stop DEF induced expansion. In addition to the steel fiber and Hoek cell testing, reinforced concrete elements were made to study the structural effects of DEF. Lastly, a series of tests performed at the University of New Brunswick were performed to assess the stresses generated by DEF and the requisite levels of confinement needed to resist these stresses. The following report outlines the process, results, and lessons learned from the conducted tests.