Repairing effect of fly ash (FA) on damage of recycled coarse aggregate was evaluated by character- istics of pores and cracks in the vicinity of interfacial transition zone (ITZ).The interfacial structure between the virgin aggregate and the attached old mortar was investigated and compared with ITZ of recycled aggregate concrete in the presence of FA or ultra-fine FA(UFA) by means of scanning electron microscope (SEM).Diam- eter and plumpness frequency distribution of pores as well as width of the old ITZ,length of contacting points and cracks density were analyzed.The SEM results reveal that the diameter of pores is decreases significantly but pores plumpness increases.A decreased ITZ width and cracks density as well as an increased bonding zone length can also been observed,which indicates that FA or UFA repairs damage of recycled coarse aggregate due to its granular effect.
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