Location
University of Leeds
Keywords
Delayed ettringite formation (DEF), diagnosis, limestone, thermodynamic modeling
Abstract
Delayed ettringite formation (DEF) in concrete causes internal swelling, which reduces the mechanical properties of concrete and can lead to issues with concrete structures due to potentially large expansive deformation. In order to address the issues of DEF-affected structures, proper assessment of the structures affected is important. However, petrographic diagnosis of concrete affected by DEF remains a controversial issue. In this paper, as case studies, diagnosis on precast concrete blocks suspected of experiencing DEF was carried out. The concrete blocks were made of white Portland cement, limestone gravel, and limestone sand mixed with copper slag. The blocks were excessively heat-cured above 80 °C. The results from polarized microscope and accelerated core expansion tests strongly indicated that DEF was the cause of the expansion. Following the analysis, the long-term laboratory tests were carried out. The results obtained through the laboratory were in agreement with the experiences in actual structures. Multi-spot analysis using SEM-EDS strongly indicated the existence of invisible ettringite, which was finely intermixed with calcium-silicate hydrate gel, which supports the paste expansion theory.
Included in
Diagnosis on Expansion of Heat-Cured Precast Concrete Blocks Due to Delayed Ettringite Formation in Japan
University of Leeds
Delayed ettringite formation (DEF) in concrete causes internal swelling, which reduces the mechanical properties of concrete and can lead to issues with concrete structures due to potentially large expansive deformation. In order to address the issues of DEF-affected structures, proper assessment of the structures affected is important. However, petrographic diagnosis of concrete affected by DEF remains a controversial issue. In this paper, as case studies, diagnosis on precast concrete blocks suspected of experiencing DEF was carried out. The concrete blocks were made of white Portland cement, limestone gravel, and limestone sand mixed with copper slag. The blocks were excessively heat-cured above 80 °C. The results from polarized microscope and accelerated core expansion tests strongly indicated that DEF was the cause of the expansion. Following the analysis, the long-term laboratory tests were carried out. The results obtained through the laboratory were in agreement with the experiences in actual structures. Multi-spot analysis using SEM-EDS strongly indicated the existence of invisible ettringite, which was finely intermixed with calcium-silicate hydrate gel, which supports the paste expansion theory.
