Abstract Carbon-black nanoparticles (CBN) have been incorporated into cement-based materials for improvement of mechanical or self-sensing properties. There is no previous research focused on the microstructural evaluation of effects of CBN on both parameters. In this work, mortars containing different CBN contents were produced, cured for 28 days, and subjected to electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. Tests for determination of compressive strength, modulus of elasticity and piezoresistivity response were developed. SEM indicated that lower CBN contents refined the cementitious matrix, while higher contents increased the volume of voids. XRD and Raman spectroscopy indicated hydration improvements for CBN contents between 0.375% and 3%. The best mechanical improvements were provided by concentrations of CBN up to 3%. CBN contents of 5% and 6% provided the best sensing properties. The optimal concentration was found to be 5% of CBN, since it provided excellent piezoresistivity, without significant mechanical properties loss.

This work presents comparative analyses of the effect of specimens' shape and size on the compressive strength and modulus of elasticity of mortars. Mortar mixtures with compressive strength between 5 and 20 MPa were produced. Experimental tests determined the compressive strength of cylinder specimens of (5 x 10) cm and (10 x 20) cm, and also cubic specimens resulted of mortar's flexural strength tests, which use (4 x 4 x 16) cm prisms. The modulus of elasticity of the cylinder specimens was also determined. Cubic specimens' compressive strength was higher than (10 x 20) cm cylinder's compressive strength and lower than (5 x 10) cm cylinder's compressive strength. The dimensions of the cylinder specimens influenced its compressive strength, which was higher for the (5 x 10) cm specimens. However, it did not affect the static modulus of elasticity of the material. Correlations between the results were established and comparisons with different authors' results were made, improving both technological control and characterization of cement-lime mortars.