Nano-technology based on depth-sensing microindentation apparatus was used to evaluate the elastic modulus and micro-hardness of the interfacial transition zone (ITZ) and to estimate the extent of the ITZ around the aggregate-matrix interface for underwater concrete (UWC) and around steel reinforcement for self-consolidating concrete (SCC) and vibrated concrete. The micromechanical properties of ITZ near to aggregates of concrete cast in water were lower than those of concrete cast in air. The modulus elasticity and the microstrength of concrete cast in water were lower than those of concrete cast in air. It is attributed to the dilution of paste cement and fines particles in water causing reduction of strength and increasing the porosity of concrete. The results of the interfacial properties between self-consolidating concrete and conventional concrete revealed that the elastic modulus and the micro-strength of the ITZ were lower on the bottom side of a horizontal steel bar than on the top side, particularly for the vibrated reference concrete. The difference of ITZ properties between top and bottom side of the horizontal steel bar appeared to be less pronounced for the SCC mixtures than for the corresponding control mixtures.