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The aim of this paper was to examine the effects of adding TiO 2 nanoparticles to cementitious compositions and partially substituting natural aggregates with recycled aggregates consisting of glass, brick, slag, or textolite, and to examine the material's ability to resist corrosion under the action of chloride ions existent in the environment that attack the steel reinforcement. The results show that the changes in the cementitious composite when it comes to the composition and microstructure influence the formation of the oxide passivating layer of the reinforcement. The addition of TiO 2 nanoparticles and recycled aggregates impacts the kinetics and corrosion mechanism of the reinforcement. An addition of 3% TiO 2 was found to be optimal for reinforcement protection. Electrochemical impedance spectroscopy confirmed the results obtained by open-circuit potential and linear polarization tests. The classification of favorable conditions indicates that compositions with recycled aggregates and 3% TiO 2 are the most effective, with compositions in which the natural aggregates were partially substituted with slag being the most effective.

Starting from the context of the principles of Sustainable Development and Circular Economy concepts, the paper presents a synthesis of research in the field of the development of materials of interest, such as cementitious composites or alkali-activated geopolymers. Based on the reviewed literature, the influence of compositional or technological factors on the physical-mechanical performance, self-healing capacity and biocidal capacity obtained was analyzed. The inclusion of TiO 2 nanoparticles in the matrix increase the performances of cementitious composites, producing a self-cleaning capacity and an anti-microbial biocidal mechanism. As an alternative, the self-cleaning capacity can be achieved through geopolymerization, which provides a similar biocidal mechanism. The results of the research carried out indicate the real and growing interest for the development of these materials but also the existence of some elements still controversial or insufficiently analyzed, therefore concluding the need for further research in these areas. The scientific contribution of this study consists of bringing together two apparently distinct research directions in order to identify convergent points, to create a favorable framework for the development of an area of research little addressed so far, namely, the development of innovative building materials by combining improved performance with the possibility of reducing environmental impact, awareness and implementation of the concept of a Circular Economy.

The use of waste from industrial activities is of particular importance for environmental protection. Fly ash has a high potential in the production of construction materials. In the present study, the use of fly ash in the production of geopolymer paste and the effect of Fe 2 O 3 , MgO and molarity of NaOH solution on the mechanical strength of geopolymer paste are presented. Samples resulting from the heat treatment of the geopolymer paste were subjected to mechanical tests and SEM, EDS and XRD analyses. Samples were obtained using 6 molar and 8 molar NaOH solution with and without the addition of Fe 2 O 3 and MgO. Samples obtained using a 6 molar NaOH solution where Fe 2 O 3 and MgO were added had higher mechanical strengths compared to the other samples.