Abstract: To study the effect of mineral admixtures on the hydration and hardening of composite binders,different cement mortars and concrete were prepared using fly ash and iron ore tailings powder whose fineness are similar with cements as active or inert mineral admixtures. The influences of different adding ratios and types of mineral admixtures on the compressive strength development as well as the 7 d-age autogenous shrinkage development were investigated under the same curing schedule and different water binder ratios. The test results show that during the initial period of the hydration process of composite binder,the fly ash and iron ore tailings powder participations have physical filling effects. The pozzolanic reactivity of fly ash increases gradually with age. In the early hydration period,the physical properties of mineral admixtures (such as the particle shape,etc.),other than its chemical properties (such as degree of reaction,etc.) have an overwhelming effect on the compressive strength of mortar samples. The autogenous shrinkages of concrete with different admixtures show similar changing trends,which both decrease with the increasing adding ratios.