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The aim of this study is to analyze the effect of the addition of TiO2 nanoparticles (NTs) on the physical and mechanical properties, as well as the microstructural changes, of cementitious composites containing partially substituted natural aggregates (NAs) with aggregates derived from the following four recycled materials: glass (RGA), brick (RGB), blast-furnace slag (GBA), and recycled textolite waste with WEEE (waste from electrical and electronic equipment) as the primary source (RTA), in line with sustainable construction practices. The research methodology included the following phases: selection and characterization of raw materials, formulation design, experimental preparation and testing of specimens using standardized methods specific to cementitious composite mortars (including determination of apparent density in the hardened state, mechanical strength in compression, flexure, and abrasion, and water absorption by capillarity), and structural analysis using specialized techniques (scanning electron microscopy (SEM) images and energy dispersive X-ray spectroscopy (EDS)). The analysis and interpretation of the results focused primarily on identifying the effects of NT addition on the composites. Results show a decrease in density resulting from replacing NAs with recycled aggregates, particularly in the case of RGB and RTA. Conversely, the introduction of TiO2 nanoparticles resulted in a slight increase in density, ranging from 0.2% for RTA to 7.4% for samples containing NAs. Additionally, the introduction of TiO2 contributes to improved compressive strength, especially in samples containing RTA, while flexural strength benefits from a 3–4% TiO2 addition in all composites. The compressive strength ranged from 35.19 to 70.13 N/mm2, while the flexural strength ranged from 8.4 to 10.47 N/mm2. The abrasion loss varied between 2.4% and 5.71%, and the water absorption coefficient varied between 0.03 and 0.37 kg/m2m0.5, the variations being influenced by both the nature of the aggregates and the amount of NTs added. Scanning electron microscopy (SEM) images and energy dispersive X-ray spectroscopy (EDS) analysis showed that TiO2 nanoparticles are uniformly distributed in the cementitious composites, mainly forming CSH gel. TiO2 nanoparticles act as nucleating agents during early hydration, as confirmed by EDS spectra after curing. [ABSTRACT FROM AUTHOR]

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 TiO2 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. [ABSTRACT FROM AUTHOR]

The development of biofilms of micro-organisms on the surface of buildings, in addition to the negative impact and risk to the health of the population, leads to their degradation and the need for continuous sanitation operations. Inducing superhydrophilicity and self-cleaning performance of cement surfaces by adding TiO2 nanoparticles to the composite matrix, as a result of photoactivation reactio. This method, can become an effective for the production of new materials in order to increase the durability of buildings and to increase the degree of hygiene, due to the ability of these new materials to inhibit the growth of microorganisms. Experimental results have shown that in case of contamination with two types of moulds (Aspergillus niger, Penicillium notatum) and four types of bacteria (Escherichia Coli, Pseudomonas Aeruginosa, Staphylococus Aureus, Streptococus Pyogenes) respectively, the development of harmful biofilm is inhibited. This performance was monitored using the dimensional development of the specific inhibition halo as a quantifiable indicator. It can be said that it is influenced by the type of contaminant and the nanoparticle content of the cementitious composite matrix, but is manifested in all cementitious composites containing TiO2 nanoparticles photoactivated under laboratory conditions. [ABSTRACT FROM AUTHOR]

The effect of the use of TiO2 nanoparticles in the production of cementitious composites, worldwide already known, represents an area of interest for the development of materials with self-cleaning capacity; antimicrobial, antibacterial, antifungal properties; and to contribute to the reduction of environmental pollution. This paper aims to analyze the influence that TiO2 nanoparticles have on the cementitious matrix regarding hydrophilicity, this being one of the two main parameters of the self-cleaning mechanism. Experimental tests, conducted by using the indirect method of measuring the surface water absorption, indicated that an addition of 3%-6% (relative to the amount of cement) of TiO2 nanoparticles is effective in terms of increasing the surface hydrophilicity of the cementitious composites. An excess of TiO2 nanoparticles in the composite matrix (10% TiO2 nanoparticles relative to the amount of cement) not only does not improve surface performance in terms of hydrophilicity, but also reduces them. However, in practice on a case-by-case basis, an analysis is required regarding the optimal amount of nanoparticles used as an addition in the mix-design of the cementitious materials that are intended to induce the quality of self-cleaning process, depending on the intended use, climate, degree and duration of sunlight, and so on. [ABSTRACT FROM AUTHOR]

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The development of mold films on the cement surfaces of buildings is a health and safety problem for the population, aesthetic but also in terms of their durability. The use of specific performance of cementitious composites containing TiO2 nanoparticles, photoactivated by UV radiation, can be a viable solution to mitigate to eliminate these problems. The experimental studies presented aim to analyze the capacity to inhibit the development of mold type Aspergillus and Penicillium on the surface of composite materials with nano-TiO2 content and the identification of the optimal range of nanomaterial addition. The identification and analysis of the inhibition halo (zone with a biological load of maximum 1–10 colonies of microorganisms) confirmed the biocidal capacity of the cementitious composites, but also indicated the possibility that an excess of TiO2 nanoparticles in the mixture could induce a development of cell resistance, which would be unfavorable both in terms of behavior and in terms of cost. [ABSTRACT FROM AUTHOR]

The formation of biofilms on cementitious building surfaces can cause visible discoloration and premature deterioration, and it can also represent a potential health threat to building occupants. The use of embedded biofilm-resistant photoactivated TiO2 nanoparticles at low concentrations in the cementitious composite matrix is an effective method to increase material durability and reduce maintenance costs. Zone of inhibition studies of TiO2-infused cementitious samples showed efficacy toward both Gram-negative and Gram-positive bacteria. [ABSTRACT FROM AUTHOR]