Alternative binders based on the use of portland cement should provide the same functionality and durability as conventional cement binders. One area of growing interest involves binders in which cement is partially replaced by nanoparticles, which are known to possess unique physico-chemical properties. A good reason to perform the research described in this doctoral dissertation was the lack of knowledge about how to modify the nanoscale microstructure of the cement binder in such a way that cement composites made using such a binder would have better-performing characteristics. The chemically inert nanoparticles selected were α-Al2O3. The agglomeration of such particles always causes considerable problem; in this case they were resolved by mixing the components by means of a two-step procedure through a combination ultrasonication and the addition of a surface active agent, a polycarboxylate type superplasticizer was selected. Taking into account the semi-empirical Krieger-Dougherty relationship, the maximum solid volume fraction of the cement suspensions, was calculated. The results showed a uneven reduction in the measured values, with an increasing replacement level of cement by α-Al2O3 nanoparticles. This observed reduction was attributed to a combination of two opposing effects, the filler effect and the specific surface area effect – the latter effect was somewhat stronger than the former effect. The results obtained during the middle period of cement hydration of the cement pastes, showed that the used polycarboxylate-type superplasticizer had a stronger influence on the kinetics of cement hydration than the used α-Al2O3 nanoparticles. This confirmed that the nucleation effect of the α-Al2O3 had been significantly reduced. This reduction had a subsequent effect on the further hydration and development of the hardened microstructure. With regard to the so-called cement dilution effect, it was found that this effect increased when the nucleation effect was reduced. Hardened samples of mortar and concrete with binders incorporating nanoparticles of α-Al2O3 were characterized by lower strengths, increased overall porosity, and reduced resistance to degradation processes, as compared to the reference mortars and concretes. However, due to the increased proportion of entrapped pores, the modified samples showed improved frost resistance.