Expansion Properties and Microscopic Features of DEF and ASR Expansive Specimens Subjected to Residual Expansion Tests

It is important to distinguish between DEF (delayed ettringite formation) from ASR (alkali-silica reaction), which show similar macroscopic deterioration phenomena, using microscopic techniques. In addition to the petrographic observation, a residual expansion test of a concrete core has been proposed to distinguish DEF from ASR. In this method, concrete cores are immersed in a solution saturated with Ca(OH)2 (or water) and a 1 mol/L NaOH solution. The DEF potential is evaluated under the former condition and the ASR potential under the latter. Alkali leaching promotes DEF and alkali supply promotes ASR. However, the use of this type of the test method has been limited, and its validity has not been adequately verified. In this study, relatively large concrete specimens with DEF and ASR expansion potential were prepared under 80 ℃ pre-curing and using ASR reactive aggregate, and cores were taken for residual expansion testing. The results of the tests conducted by four institutes confirmed that the specimen with only DEF potential expanded in water and gaps filled with ettringite were observed around the aggregates. Specimens with both DEF and ASR potential expanded in both water and NaOH immersion, and the characteristics of DEF and/or ASR were identified by microscopic observation. In addition to the petrographic observation, the water and NaOH immersion tests were useful in distinguishing DEF from ASR.