Fig. 8 shows the XRD patterns of PC, 20OFA and 20CFA pastes at 28 days while the XRD patterns of PC, 40OFA and 40CFA pastes at the same age are shown in Fig. 9. It is easily noticed that CH or Ca(OH)2 is one of the hydration products during the hydration reaction. The intensity peaks of Ca(OH)2 appeared at 2h of 18.07, 28.75, 34.13, 47.12, and 50.85 degree. From the results of Figs. 8 and 9, the intensity peaks of Ca(OH)2 in the XRD patterns of the blended cement paste with fly ashes were almost similar to that of PC paste. At early ages (28 days), this result supported the hypothesis that the hydration reaction was a dominant phase while the reactivity of fly ash was minimal [16–19].