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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]

For sustainable development in construction, the concrete industry is exploring various alternatives for producing new composite materials that contribute to sustainable development. In this context, eco-innovative and low environmental impact (eco-friendly) materials such as cementitious composites, in which aggregates are substituted with waste glass, represent a future alternative. This paper presents several types of composite materials with different proportions of waste glass that can successfully replace conventional masonry mortars. [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]

Worldwide, it is now known that industrial by-products rich in silicon (Si) and aluminum (Al) can be transformed by alkaline activation into so-called "green concrete", an efficient and sustainable material in the field of construction; the geopolymer material. In this work, geopolymer materials produced using fly ash and marble dust or blast furnace slag were studied to assess the influence of these substitutions on the performances of the final product. Geopolymer materials have been characterized by physico-mechanical methods, FTIR spectroscopy and microscopically. The analysis of the results indicates the reduction of the mechanical strength performance by substituting the fly ash as the raw material. [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 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 Fe2O3, 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 Fe2O3 and MgO. Samples obtained using a 6 molar NaOH solution where Fe2O3 and MgO were added had higher mechanical strengths compared to the other samples. [ABSTRACT FROM AUTHOR]

Both Circular Economy and Sustainable Development are concepts that focus on resource efficiency. This involves a complex waste management process with a high degree of recycling and recovery. Rapid population growth and urbanization in developing countries have led to large amounts of solid waste and, consequently, increased environmental degradation of the environment. Designing resilient, sustainable materials and buildings by using recycled materials or industrial by-products, which can replace some or all of the cement, leads to the development of a sustainable, low-carbon economy and furthermore to the conservation of natural resources. Industry is developing at an accelerated pace, consequently the development of modern construction materials in the economic world is more than necessary. The aim of this research is to present preliminary results regarding the design of the alkali-activated fly ash-based geopolymer paving blocks produced using Romanian local raw materials, to present several parameters that affect their mechanical properties and to assess their intended use in terms of legislation. [ABSTRACT FROM AUTHOR]

The current global situation requires the efficient management of waste and the assessment of the potential for the implementation of the principles of the circular economy in order to conserve natural resources and reduce the negative impact on the environment. The aim of the research is to analyze the potential of non-woven products (mattresses) made of recycled polymer fibers, intended for use in the field of thermal insulation of buildings, in relation to their density and thickness. At the same time, the benefits obtained by combining them with products based on recycled waste and sheep wool were evaluated. The experimental results indicated good performance in terms of thermal conductivity coefficient and heat transfer resistance of the analyzed products, which can be successfully included in the category of heat-insulating materials. The correlation of thermal performance with the thickness and density of the products highlighted the need to deepen the analysis, these two parameters being insufficient for the design of such material. However, by combining mattresses made of recycled polymer fibers with mattresses made of recycled denim fibers and / or sheep wool, the benefits in terms of thermal insulation performance are obvious [ABSTRACT FROM AUTHOR]

The term “geopolymer” was originally introduced by the French chemist Davidovits, representing a wide range of anorganic materials. According to him, among the nine different classes of geopolymers, geopolymer concrete is of particular interest, consisting of materials containing aluminosilicates that could be used to completely replace the amount of Portland cement in ordinary concrete. The aim of this study is to present relevant data in the field of alkali-activated geopolymer materials regarding the production of this type of materials using both ambiental and heat curing and studying the differences between the two procedures. [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]