Archives of Civil and Mechanical Engineering最新文献

This study investigates the potential use of Olive Pomace Bottom Ash (OPBA) as a partial cement replacement in self-compacting mortars (SCMs) to enhance sustainability in construction while addressing environmental concerns. A Central Composite Design (CCD) approach was used to investigate the effect of OPBA content (0–20%), limestone filler content (10–20%), and water-to-binder (W/B) ratio (0.4–0.5) on fresh properties, mechanical behavior, and water absorption potential of SCM. The results indicate that increasing the OPBA content typically decreased workability and strength while at the same time increasing water absorption potential. However, this effect can be mitigated by optimizing the filler content and W/B ratio. With low additions of OPBA (up to 10%), incorporating limestone filler showed a regular increase in strength. Statistical analyses using the central composite design method confirm that complex non-linear relationships among variables exist and that advanced optimization techniques are needed in mix design. An optimal mix was found to have 6.66% OPBA, 20% filler, and a W/B ratio of 0.42, with a desirability value of 0.927. This optimal mixture recorded a slump of 26.3 cm, flow time of 11.85 s, compressive strength of 48.66 MPa, flexural strength of 5.47 MPa, and water absorption of 11%. The above study indicates that OPBA is feasible in SCMs and could improve sustainability in the construction industry without compromising performance. These findings highlight OPBA feasibility in SCMs, promoting waste valorization and reducing cement consumption without compromising performance.

The utilisation of granite powder (GP) waste in cementitious composites is limited by its low reactivity and adverse effects on mechanical performance. This study investigates the mechanical activation of GP through grinding (GP-M) and sieving (GP-S) to optimise its physical properties and sustainability potential. The modified powders were characterised in terms of specific surface area (SSA), reactivity, loss on ignition, and alkali leachability. Cementitious composites were prepared with 20% and 40% cement replacement and evaluated for slump flow, setting time, strength development, and bulk density. Results show that grinding increases the SSA from 2890 cm²/g (raw GP) to 4290 cm²/g (GP-M), improving particle packing and enhancing compressive strength by up to 20% compared to unprocessed GP. Despite its low pozzolanic reactivity, GP-M acts as an effective filler, improving microstructure and maintaining compressive strengths above 40 MPa at 28 days for 20% replacement. Alkali leachability was also reduced, supporting long-term durability. A Life Cycle Assessment (LCA) indicates that replacing 40% of cement with GP-M reduces CO₂ emissions by over 50%, while maintaining acceptable mechanical properties. The proposed Mechanical Performance Ratio (MPR) and Environmental Performance Ratio (EPR) demonstrate that the most balanced performance was achieved in the GP-M20 and GP-S20 series, offering up to 12% CO₂ savings with minimal strength reduction. This study confirms that mechanically valorised granite powder is a viable, sustainable SCM, capable of reducing cement content while satisfying structural and environmental requirements in construction applications.

Explosive welding is an effective method for joining metals with dissimilar physicochemical properties. The Al/Ni system is particularly interesting due to the formation of intermetallic phases with unique mechanical and thermal properties, which makes these welds potentially applicable in industries, such as aerospace, energy, and chemical. Diffusion processes occurring at the interface between these metals play a significant role and can impact the durability of the connections. Therefore, this research focuses on the analysis of diffusion phenomena in Al/Ni welds formed by explosive welding and subjected to further annealing. It was investigated whether the technological parameters of the joining process, such as detonation velocity, which varied from 2000 to 2800 m/s or mutual localization of the colliding plates during the explosion, influence post-annealing interface transformations, in particular the sequence of the intermetallic phase formation, their thickness and growth mechanism. Welded clads underwent annealing at 500 °C for periods ranging from 0.5 to 168 h. After the heat treatment, microstructure and phase characterization of the interface zone were performed, with scanning and transmission electron microscopy, thanks to which the mechanisms and growth kinetics of the forming phases were determined. Additionally, for the first time, the anisotropy of the thermal expansion in explosively welded Al/Ni was examined with respect to the shock wave propagation and the accompanying microstructure evolution, providing a significant contribution to the engineering design of welds subjected to the thermal cycling. The thermal expansion coefficient was measured over the temperature range from ambient temperature to 500 °C and analyzed in relation to the welding conditions. Differences in the thickness of the two forming Al₃Ni and Al₃Ni₂ layers and their dominant growth mechanisms were observed for the individual clads. The effect of detonation velocity was particularly significant at 2000 m/s, where prolonged annealing led to weld degradation, thus limiting strength due to unfavorable welding conditions. The presence of porosity identified at the Al1050/Al₃Ni₂ interface was attributed to the Kirkendall effect accompanying the annealing procedure. Measurements of the thermal expansion coefficient revealed minor differences between samples, with the largest discrepancies observed for clads produced at 2400 m/s, which may be due to the less uniform initial microstructure of the interface. The obtained results indicate a relationship between explosive welding conditions and changes in the microstructure and physical properties of Al/Ni welds after heat treatment.

In the present research, free vibration of a truncated conical shell is investigated. The shell consists of three layers: a porous core and two carbon nanotube-reinforced nanocomposite (CNTs-RNC) facesheets. The structure is inserted in a thermal environment and also, is also subjected to a longitudinal magnetic field. The structure’s kinematics is modelled based on the first-order shear deformation theory (FSDT), and the modified coupled stress theory (MCST) is used to consider the scale effect. The equations of motion are derived using Hamilton’s principle, and then, the generalized differential quadrature method (GDQM) is employed to solve them under various combinations of boundary conditions. The effects of several parameters, including geometry, porosity coefficient, porosity distribution patterns, CNTs’ mass fraction and types, agglomeration coefficients, boundary conditions, and small-scale parameter are investigated. The results demonstrate that the natural frequency increases with increasing CNTs’ mass fraction and decreases with increasing porosity. These structures have a wide range of potential applications and can be used in microelectromechanical and nanoelectromechanical systems.

Large anisotropy of the tensile strength-ductility combination of the laminated twin/matrix (T/M) structure was found by studying the mechanical response of pre-twinned Cu-8at.%Al crystal structures, subjected to plastic tension under the different loading conditions. Three resolved shear stress-driven mechanisms, M¹, M², M³, were introduced to describe the deformation properties of the bimodal T/M structure. The “zero” tensile ductility (ε_T) accompanied by the tensile strength σ_T about 550 MPa or above 900 MPa was established when the T/M structure was loaded almost parallel (M³) or perpendicular (M¹) to the T/M interface. Consequently, the T/M structure revealed the minimal (“zero”) tensile strength-ductility combination (σ_T × ε_T), when plastic yielding was initiated by M¹ or M³ mechanism; both connected with T/M lattice shears occurring across the T/M interface. However, the T/M structure loaded at an angle about π/4 to the T/M interface revealed exceptionally large ductility (true strain equal to unity) accompanied by true stress of 850 MPa, i.e., the maximal combination σ_T × ε_T of 850 MPa, projected to about 1500 MPa for an analogous T/M structure of high manganese steels. All the “non-zero” cases of σ_T × ε_T were determined by activity of M² mechanism, i.e., T/M lattice shear parallel to the T/M interface. The σ_T × ε_T values depended on the length of M² deformation path terminated by a sudden entry of M³ (M¹) mechanism. The entry, governed by the Schmid–Boas law, occurred always well before the Considère condition was met. The physical reasons of the observed anisotropy of the T/M structure are discussed.

This study successfully obtained 7A85 high-ribbed panels friction stir-welded (FSW) joints through proportional parameter changed (ω: 400–1200 rpm; v: 100–300 mm/min) and further optimized the mechanical properties of the FSW joints through artificial aging. The effects of welding process parameters and artificial aging on the microstructure and mechanical properties of the welded joint were investigated using OM, SEM, EBSD, TEM, tensile testing, and hardness testing. The results showed that the joint consists of the weld nucleus zone (NZ), thermomechanical influence zone (TMAZ), heat-affected zone (HAZ) and base metal (BM). Among these, the NZ undergoes significant dynamic recrystallization under thermomechanical coupling, with the degree of recrystallization increasing gradually from top to bottom along the thickness direction. When the welding pitch remains constant, increasing the welding speed reduces heat input and effectively suppresses the coarsening of precipitates in the HAZ. After aging, the GP zone in the NZ transforms into the strengthening η′ phase, while the coarsening in the HAZ is further suppressed. Mechanical tests indicate that increasing the parameters from ω = 400 rpm/v = 100 mm/min to ω = 1200 rpm/v = 300 mm/min can enhance tensile strength from 432 to 463 MPa, yield strength from 332 to 377 MPa, while reducing elongation from 6.2% to 5.2%. Increasing the proportional parameters enhances strength with limited loss of elongation, but expands the weakened zone of the TMAZ/HAZ. Therefore, welding process parameters of ω = 800 rpm and v = 200 mm/min yield excellent microstructural characteristics and optimal performance.

Austenitic ductile iron, also known as Ni-resist cast iron, belongs to the cast iron group, which is characterized by a high-nickel content ranging from 18% to 36% by weight. Although this level of nickel content significantly increases the production costs, it imparts numerous beneficial properties that justify the price. One notable property is its ability to operate across a wide temperature range, with a minimum service temperature of − 200 °C, and a maximum, depending on the grade, reaching up to 1050 °C. This family of high-quality alloys demonstrates mechanical properties, where grades without carbide-forming elements achieve elongation exceeding 40%. On the other hand, by adding Cr, which is a carbide-forming element, the Ni-resist cast iron’s plasticity decreases, while its corrosion resistance properties increase. However, a comprehensive investigation into the correlation between mechanical properties and corrosion resistance, particularly in relation to various nickel contents in the presence of Cr in high-nickel cast iron, is scarce. Therefore, the primary aim of this study was to elucidate the role of nickel content and chromium content in influencing the mechanical and corrosion resistance properties of austenitic ductile iron. The addition of 21, 25, 28, and 35 wt% of nickel with and without 2.5 wt% of chromium was investigated. Characterization of the materials was carried out using optical and scanning electron microscopy, static tensile tests, impact strength tests, and corrosion resistance assessments at room temperature in a 3.5 wt% NaCl solution. The investigation revealed a significant influence by changing the nickel and chromium content on the properties of high-nickel cast iron. In addition, it was proved that by controlling the content of these elements, the cast iron with establish properties can be achieved—depending on expected final properties, results show that it is possible to substitute part of the nickel content with smaller amount of chromium to get similar corrosion resistance properties and reduce the production costs, but it will influence to mechanical properties, which dependent on plasticity.

In the first part of the work, the 3-step homogenization procedure was carried out for AlMgSi(Cu) alloy, aimed at obtaining billets microstructure with numerous fine particles of strengthening phases and increased solidus temperature. In the second part of the work, an original on a global scale prototype device for the dynamic stretching of extruded profiles before artificial ageing, was proposed and tested in semi-industrial conditions. The thermo-mechanical treatment of extruded hollow profiles from AlMgSi(Cu) alloy with 1.22% content of copper was performed with dynamic deformation range: 0.25%, 0.5%, 1%, 1.5% and 2%. The microstructural inspection was performed in the welding area and outside the weld for variant after only extrusion and for variant after extrusion and dynamic stretching before artificial ageing. It was revealed that the designed three-stage homogenization treatment led to dissolution of soluble phases present in the as-cast billets microstructure, which caused significant increase in solidus temperature, from 509 °C in as-cast state to 573 °C after completed soaking. The application of dynamic deformation during the straightening of aluminium profiles after hot extrusion with water cooling on the press run, led to the induced favourable changes in the microstructure of the alloy, which translated into a significant increase in UTS of about 11%.

3D printing introduces unique challenges in construction, particularly regarding fire safety. The layer-by-layer deposition leads to potential weaknesses such as interlayer debonding, spalling, and cracking when exposed to elevated temperatures and thermal gradients. Despite growing interest, large-scale fire performance of 3D-printed concrete (3DPC) remains underexplored. This study investigates the thermal and fire behaviour of 3DPC, both material wise and of printed full scale. Laboratory tests on small specimens (160 × 40 × 40 mm) assessed the mechanical performance of 3D-printed concrete exposed to temperatures up to 800 °C. The results show that over 80% of compressive strength was retained after heating the samples to 450 °C. Full-scale wall segments (500 mm × 180 mm × 500 mm) with three different internal topologies (hollow, triangular, and sinusoidal) were subjected to standard fire resistance tests. Elements with attached thermocouples were fixed in the oven without a load and exposed to ISO 834 temperature–time profile. The occurring damage on the exposed and unexposed surface was evaluated using optical measurements. Results has shown that the elements maintained integrity (E) and insulation (I) criteria up to 450 °C at 1 cm depth for 19–25 min, and at 2 cm for 45–65 min. Tests revealed extensive surface cracking in all samples, with the most significant damage observed in hollow-core elements. In contrast, samples with triangular and sinusoidal infill exhibited lower thermal penetration and reduced structural degradation. The findings indicate promising thermal insulating performance of 3DPC and highlight the critical role of internal geometry in fire response. However, further research is required to assess fire behaviour under mechanical loading and to validate performance across a wider range of infill designs and real-scale conditions.

This study explores the potential of carbon dioxide sequestration to enhance the properties of recycled concrete aggregate (RCA) through accelerated carbonation techniques. Carbonated RCA (CRCA) was incorporated into concrete mixtures with two water–cement ratios (0.55 and 0.42), targeting compressive strengths of 30 MPa and 40 MPa, respectively. RCA particles (5–20 mm) were carbonated under 1 bar pressure for 2 and 3 h. Key physical properties including aggregate crushing value (ACV), aggregate impact value (AIV), and water absorption (WA), were evaluated for both RCA and CRCA. Results showed that CRCA significantly improved concrete workability and strength compared to untreated RCA. Specifically, CRCA reduced ACV, AIV, and WA by 2.8%, 2.3%, and 1.5%, respectively, indicating better aggregate quality. In 30 MPa concrete, compressive strength increased by 16% with 100% CRCA and by 9.6% with 50% CRCA; for 40 MPa concrete, the improvements were 18% and 12%, respectively. Similar trends were observed for split tensile strength. Microstructural analyses (XRD, FTIR, TGA, DSC, SEM) confirmed that carbonation at 1 bar for 2 h provided optimal RCA modification. These findings suggest that accelerated carbonation of RCA can substantially improve concrete performance, offering practical benefits for sustainable construction practices.