2016 Volume 70 Issue 1 Pages 2-8
Sulfate attack is known as one of the deterioration phenomena of concrete structure. Especially, expansion due to delayed ettringite formation（DEF）has been serious problem nowadays. According to previous researches, continuous water supply and temperature history above 70℃ are needed for DEF expansion. However, DEF expansion mechanisms are still unclear. Therefore, the purpose of this research is to discuss that behavior of water molecules and structural changes of ettringite in relation to the mechanism of DEF and expansion in terms of dehydration and rehydration of ettringite.
From the experimental results, after dehydration by heating above 80℃ 12 hours, water molecules bonded to SO42- in ettringite structure were removed and dehydrated ettringite was amorphous on XRD；ettringite was converted into meta-ettringite. Furthermore, the amount of water desorption isotherm in rehydrated meta-ettringite was decreased significantly about R.H. 15％. In addition, reduction of density of rehydrated meta-ettringite were observed. Therefore, there were possibility that rehydrates of meta-ettringite possibly have ink-bottled pores of nanometer scale and closed pores.
