New experimental approach to accelerate the development of internal swelling reactions (ISR) in massive concrete structures

Abstract

Internal Swellings Reactions (ISR) are pathologies that are likely to degrade concrete by causing swelling, cracking and major disorders in structures. Many laboratory studies of internal swelling reactions are realized on relatively small size samples. Those laboratory samples do not allow to replicate real conditions to which the real concrete is submitted in its environment, in terms of aging kinetics, ionic transport, early age thermal history and mechanical conditions especially in massive structures. Therefore, an experimental approach to accelerate internal swelling reactions of concrete at the structure scale is developed to allow better observation and understanding of swelling reactions at a massive structure scale. Two representative massive concrete structures (2.4 × 1.4 × 1 m3) were realized under controlled and optimized conditions for the development of alkali-silica reaction (ASR) and delayed ettringite formation (DEF). An instrumentation system is developed thus allowing to monitor evolutions of the pathologies in the massive structures both internally and externally. The respective deformations and cracking were tracked for over 3 years. Results show different swelling kinetics and amplitudes among the mock-ups and allow validating the proposed approach. Expansions in massive structures vary greatly from analogous laboratory samples. Boundary conditions and confinement effects could hinder swelling along certain directions thus compensated by a higher expansion along unstressed directions which leads to an anisotropic behavior in the material and impacts the cracking orientation. Residual swelling tests reveal the chemical potential of the internal swelling reactions and define an upper strain limit for the structure. They reveal as well a scale effect on the reactional kinetics and on the swelling amplitude.