Mustansiriyah Journal of Materials Engineering and Sustainability

The growing production of industrial by-products and the growing amount of construction and demolition waste have created a range of environmental problems associated with natural resource exhaustion and overburdened landfills. As far as construction and demolition waste is concerned, components such as silica fume and ceramic floor waste have shown some promising features in terms of physical and chemical compatibility with cement-based compositions. The present study focuses on evaluating the effects of using SF as a cement replacement material and CW as a fine aggregate substitute on the performance properties of cement mortar. Altogether, 13 mixes were tested: one control mix, four SF mixes (5%, 10%, 15%, and 20% by weight of cement), four CW mixes (10%, 20%, 30%, and 40% by weight of sand), and four combined SF-CW mixes (10% SF with 10%, 20%, 30%, and 40% CW). Flow tests, setting time determination, compressive strength, flexural strength, and ultrasonic pulse velocity tests were performed, along with scanning electron microscopy. The results showed that the optimal single substitution was 10% SF, reaching a compressive strength of 51.1 MPa, which represents net increase 9 MPa compared to the control specimen (42.1 MPa). The highest compressive (56.1 MPa), flexural (7.5 MPa), and UPV (4.614 km/s) values were observed for the SFC20 composition (10% SF + 20% CW), which indicated a synergetic effect in terms of the density of the material. An increase in both replacements resulted in a decrease in workability.

Concrete is the most widely used construction material for these purposes. However, its longevity is frequently compromised by cracking, permeability, chloride penetration, sulfate attack, and associated deterioration processes. Nanomaterials can enhance cementitious composites through pore refinement, accelerated hydration, densification of the interfacial transition zone, and crack-control behavior. The current critical review is focused on the evaluation of the impact of nano-silica (NS), carbon nanotubes and carbon nanofibers (CNTs/CNFs), nano-titanium dioxide (nano-TiO₂), nano-alumina (nano-Al₂O₃), nanoclay, and graphene oxide (GO) on the mechanical and durability performance of concrete. Generally speaking, nano-silica has the highest potential among nanomaterials for providing a consistently high strength increase of about 10-35%, reduction of water absorption, and chloride migration in the range of 20-60%. Meanwhile, carbon-based nanomaterials tend to have a higher potential for improving the tensile and flexural properties of concrete, which is usually observed at 15-50%. Nano-TiO₂ gives rather modest mechanical properties but also provides photocatalytic activity. At the same time, nano-Al₂O₃, nanoclay, and GO have the potential for densifying the matrix, reducing permeability, sulfate resistance, and crack control. It should be noted that all reported values depend on the specific features of the nanoparticles, their dosage, distribution quality, concrete composition, curing regime, and testing procedure. Widespread implementation is restricted by agglomeration, increased demand for water, high prices, lack of field validation, health hazards, and lack of testing standards. Overall, nano-silica shows the best combination of performance and feasibility, whereas carbon-based nanomaterials and GO are applicable only in specialized cases.

Cellulose, the most prevalent biopolymer on Earth, has proven to be an effective multifunctional material for enhancing the performance of concrete and other cement-based products. The current review analyzes recent developments in the application of cellulosic polymers in concrete and cement composites, including microcrystalline cellulose (MCC), cellulose nanofibrils (CNF/NFC), cellulose nanocrystals (CNC), carboxymethyl cellulose (CMC), and hydroxypropyl methylcellulose (HPMC). Special attention is paid to their interfacial interactions with cement hydration products, modes of incorporation, and impact on the properties of fresh concrete and performance of hardened materials (mechanical performance, transport properties, durability, etc.). According to published data, the addition of CNF in an amount of approximately 0.1 wt. % results in a 106% enhancement of flexural strength and a 184% increase in energy absorption capacity. Meanwhile, the flexural strength was enhanced by CNC (approximately 0.2 vol. %) by approximately 30%. Ultra-high-performance concrete containing nanocellulose experienced a 45-75% reduction in autogenous shrinkage in the initial 24 h. Nevertheless, the effects and signs of these improvements are strongly determined by the cellulose structure, dosage, surface chemistry, dispersion quality, consumption of water, cement formulation, and other parameters, which must be controlled because excessive amounts of cellulose and its improper dispersion could negatively influence the workability, hydration process, and strength development. In addition, potential drawbacks such as agglomeration, requirement for high energy input for dispersion, incompatibility with certain chemical admixtures, durability under aggressive environments, and other factors are considered in this review.

The development of advanced metallic alloys for aerospace applications is continuously progressing to meet new requirements for lightweight construction, energy efficiency, high-temperature operation, durability, and sustainability. The state-of-the-art regarding the most common metallic alloy families currently used in aerospace engineering is presented in this review. These alloys include traditional aluminum alloys, aluminum-lithium alloys, titanium alloys, nickel-based superalloys, and advanced high-entropy alloys (HEAs). The compositions, microstructures, processing methods, potential of additively manufactured parts, mechanical properties, and sustainability characteristics of these alloys were critically evaluated. Third-generation Al-Li alloys provide approximately 2-4% decrease in density and up to 10% increase in stiffness compared to conventional 2xxx and 7xxx aluminum alloys, which makes their use very effective in reducing the weight of structural elements. Titanium alloys still cannot be replaced in aerospace structural applications at medium temperatures, whereas nickel-based superalloys are widely used in turbines operating at temperatures higher than 1100-1200°C. High-entropy alloys demonstrate an outstanding combination of strength, ductility, resistance to corrosion, and high-temperature stability, with several lightweight alloys demonstrating compressive yield strengths higher than 1300 MPa at temperatures close to 1000°C. Additive manufacturing techniques have considerably promoted the adoption of topology-optimized aerospace parts; however, fatigue behavior, qualification, and certification remain problematic issues. Moreover, sustainability concerns, including embodied carbon, recyclability, and lifetime impacts, play a more important role in selecting the optimal alloy. Finally, the gaps in the research regarding long-term fatigue behavior, qualification approaches, manufacturing scalability, and machine learning-based alloy design are discussed and prioritized.