The early-age hydrates and paste structure of complex binders composed of Portland cement, mineral admixture and expansive agent were investigated with XRD and ESEM. The hydrates begin to nucleate at the 6~(th) hour. Fiber-form CSH and plate-form ettringite microcrystals, as well as temporary products of syngenite and K_2SO_4 are formed in this period. A large amount of hydration products, mainly CSH, Ca(OH)_2 and ettringite, are formed after 1 day to produce a dense paste.