Coexistence of alkali silica reaction and delayed ettringite formation in a cracked high performance concrete element

The concrete cores drilled from a cracked elements were examined by various testing methods to clarify the cracking of some concrete elements after 4-years in service. The chemical and mineral compositions of the paste in concrete cores were characterized by chemical analysis, X-ray fluorescence, X-ray diffraction and thermogravimetric analysis. The microstructure of the cores was analyzed by the petrographic method and scanning electron microscopy/energy dispersive spectrum. The results show that the amount of fine aggregates and some coarse aggregates show typical signs of the alkali-silica reaction. Ettringites with various morphologies were richly formed in the interfacial transition zone (ITZ) between aggregate and paste. The coexistence of the alkali-silica gel and ettringite also occurs in the ITZ between aggregate and paste. The deterioration of the concrete elements is a typical case caused by the combination of alkali silica reaction and delayed ettringite formation.