Search Results (38)

This research investigates the feasibility of producing eco-friendly self-compacting concrete (SCC) by partially replacing both fine and coarse natural aggregates with waste marble sludge (WMS), a byproduct of the marble industry. The objective is to evaluate whether this substitution enhances or compromises the concrete’s performance while contributing to sustainability. A comprehensive experimental program was conducted to assess fresh and hardened properties of SCC with varying WMS content. Fresh-state tests—including slump flow, T₅₀ time, and V-funnel flow time—were used to evaluate workability, flowability, and viscosity. Hardened properties were measured through compressive, flexural, and Brazilian tensile strengths, along with water absorption after 28 days of curing. The mix with 10% replacement of both sand and coarse aggregate showed the most balanced performance, achieving a slump flow of 690 mm and a V-funnel time of 6 s, alongside enhanced mechanical properties—compressive strength 48.6 MPa, tensile strength 3.9 MPa, and flexural strength 4.5 MPa—and reduced water absorption (4.9%). A complementary cost model quantified direct material cost per cubic meter and a performance-normalized efficiency metric (compressive strength per cost). The cost decreased monotonically from 99.1 $/m³ for the base mix to $90.7 $/m³ at 20% + 20% WMS (−8.4% overall), while the strength-per-cost peaked at the 10% + 10% mix (0.51 MPa/USD; +12% vs. base). Results demonstrate that WMS can simultaneously improve rheology and mechanical performance and reduce material cost, offering a practical pathway for resource conservation and circular economy concrete production. Full article

This study investigated the changes in the acoustic emission (AE) activity emitted in fiber-reinforced concrete (FRC) under flexure at two temperatures (25 °C and −20 °C). Seven concrete mixtures were developed with different water-binder ratios (w/b) (0.4 and 0.55), different fiber materials (steel fiber (SF) and synthetic polypropylene fiber (Syn-PF)), different fiber lengths (19 mm and 38 mm), and various Syn-PF contents (0%, 0.2%, and 1%). Prisms with dimensions of 100 × 100 × 400 mm from each mixture underwent a four-point monotonic flexure load while collecting the emitted acoustic waves via attached AE sensors. AE parameter-based analyses, including b-value, improved b-value (Ib-value), intensity, and rise time/average signal amplitude (RA) analyses, were performed using the raw AE data to highlight the change in the AE activity associated with different stages of damage (micro- and macro-cracking). The results showed that the number of hits, average frequency, cumulative signal strength (CSS), and energy were higher for the waves released at −20 °C compared to those obtained at 25 °C. The onset of the first visible micro- and macro-cracks was noticed to be associated with a significant spike in CSS, historic index (H (t)), severity (S_r) curves, a noticeable dip in the b-value curve, and a compression in bellows/fluctuations of the Ib-value curve for both testing temperatures. In addition, time and load thresholds of micro- and macro-cracks increased when samples were cooled down and tested at −20 °C, especially in the mixtures with higher w/b, longer fibers, and lower fiber content. This improvement in mechanical performance and cracking threshold limits was associated with higher AE activity in terms of an overall increase in CSS, S_r, and H (t) values and an overall reduction in b-values. In addition, varying the concrete mixture design parameters, including the w/b ratio as well as fiber type, content, and length, showed a significant impact on the flexural behavior and the AE activity of the tested mixtures at both temperatures (25 °C and −20 °C). Intensity and RA analysis parameters allowed the development of two charts to characterize the detected AE events, whether associated with micro- and macro-cracks considering the temperature effect. Full article

The increasing environmental impacts caused by the high demand for concrete production have underscored the need for sustainable alternatives in the design of eco-concrete mixtures. Additionally, important industries, such as construction and mining, generate massive amounts of waste/by-products that could be repurposed towards sustainability. Consequently, this study investigates the valorization of copper slag (CS), a by-product of the mining industry as a supplementary cementitious material (SCM), and concrete as recycled coarse aggregate (RCA), derived from construction and demolition waste, as partial substitutes for Ordinary Portland Cement (OPC) and natural coarse aggregate (NCA), respectively. Eco-concrete mixtures were designed with varying replacement levels: 15% for CS, and 0%, 20%, 50%, and 100% for RCA. The mechanical properties (compressive, indirect tensile, and flexural strengths), permeability characteristics (porosity and capillary suction), and environmental impacts (carbon footprint) of these mixtures were evaluated. The results showed that the use of CS and of increasing proportions of RCA led to a monotonic loss in each of the concretes’ mechanical strength properties at 7, 28 and 90 days of curing. However, at extended ages (180 days of curing), the concrete mixtures with CS and only NCA presented an average compressive strength 1.2% higher than that of the reference concrete (mixture with only OPC and natural aggregate). Additionally, the concrete mixture with CS and 20% RCA achieved 3.2% and 5.8% higher average values than the reference concrete in terms of its indirect tensile strength and flexural strength, respectively. Finally, a cradle-to-gate life cycle assessment (LCA) analysis was implemented, whose results showed that the greatest effect on reducing the carbon emission impacts occurred due to the substitution of OPC with CS, which confirmed that the adequate technical performances of some of the concrete mixtures developed in this study are positively complemented with reduced environmental impacts. Moreover, this study presents a viable approach to minimizing resource consumption and waste generation, contributing to the advancement of eco-friendly construction materials, which aligns with the sustainable development goals. Full article

In this study, graphite tailings produced in Luobei County, Heilongjiang Province, were used as a sustainable aggregate to replace river sand (0%, 25%, 50%, 75%, 100%) in UHPC for the preparation of ultra-high-performance concrete (UHPC). The experimental results showed that the incorporation of 75% graphite tailings caused a significant increase in the wet bulk density of UHPC mortar. The workability of UHPC decreased monotonically with the increase in graphite tailing substitution rate, and wet bulk density decreased by 28.42% with 100% graphite tailings (compared with no graphite tailings). The incorporation of 75% graphite tailings helped to improve the compressive and flexural strengths as well as the durability of UHPC. Compared with the UHPC without graphite tailings, the 28 d compressive and flexural strengths increased by 8.82% and 7.28%, respectively, and the chloride ion electrical flux decreased by 19.49%. XRD and thermogravimetric analysis data indicate that the incorporation of graphite tailings did not change the type of hydration and that the incorporation of graphite tailings helped to increase the degree of hydration within the UHPC matrix. MIP and SEM showed that 75% graphite tailings helped to reduce the porosity and the number of harmful pores inside the matrix. The 100% graphite tailings treatment replacing river sand decreased the economic cost of UHPC by up to 23.78%. Full article

Concrete columns are considered critical elements with respect to the stability of buildings during earthquakes. To improve the accuracy of column damage and collapse risk estimates using numerical simulations, it is important to develop a methodology to quantify the effect of displacement history on column force–deformation modeling parameters. Addressing this knowledge gap systematically and comprehensively through experimentation is difficult due to the prohibitive cost. The primary objective of this study was to develop guidelines to simulate the lateral cyclic behavior and axial collapse of concrete columns with different modes of failure using continuum finite element (FE) models, such that wider parametric studies can be conducted numerically to improve the accuracy of assessment methodologies for critical columns. This study expands on existing FEM research by addressing the complex behavior of columns that experience multiple failure modes, including axial collapse following flexure–shear, shear, and flexure degradation, a topic which has been underexplored in previous works. Nonlinear FE models were constructed and calibrated to experimental tests for 21 columns that sustained flexure, flexure–shear, and shear failures, followed by axial failure, when subjected to cyclic and monotonic lateral displacement protocols. The selected columns represented a range of axial loads, shear stresses, transverse reinforcement ratios, longitudinal reinforcement ratios, and shear span-to-depth ratios. Recommendations on optimal material model parameters obtained from a parametric study are presented. Metrics used for optimization include crack widths, damage in concrete and reinforcement, drift at initiation of axial and lateral strength degradation, and peak lateral strength. The capacities of shear–critical columns calculated with the optimized numerical models are compared with experimental results and standard equations from ASCE 41-17 and ACI 318-19. The optimized finite element models were found to reliably predict peak strength and deformation at the onset of both lateral and axial strength failure, independent of the mode of lateral strength degradation. Also, current standard shear capacity provisions were found to be conservative in most cases, while the FE models estimated shear strength with greater accuracy. Full article

The surface of dental materials is exposed to various prophylaxis protocols during routine dental care. However, the impact of these protocols on the functional properties of the material’s surface remains unclear. This study investigates the influence of different dental prophylaxis protocols on the surface properties and their effect on the mechanical performance of CAD-CAM restorative materials. Discs (Ø = 15 mm, thickness = 1.2 mm) were fabricated from resin composite (RC, Tetric CAD), leucite-reinforced (LEU, IPS Empress CAD), lithium disilicate (LD, IPS e.max CAD), and zirconia ceramics (ZIR, IPS e.max ZirCAD MT). The materials were subjected to six prophylactic treatments: untreated (CTRL), prophylactic paste fine (PPF), prophylactic paste coarse (PPC), pumice stone (PS), air abrasion with sodium bicarbonate jet (BJ), and ultrasonic scaling (US). Biaxial flexural fatigue tests, along with fractographic, roughness, and topographic analyses, were conducted. No significant changes in fatigue strength were observed for RC, LD, and ZIR under any prophylaxis protocols. However, LEU subjected to BJ treatment exhibited significantly reduced fatigue strength (p = 0.004), with a 22% strength reduction compared to the monotonic test and substantial surface alterations. Surface roughness analyses revealed increased roughness for RC treated with PPF, PPC, and PS compared to CTRL (p < 0.05), while LD exhibited decreased roughness following PPF, PS, and US treatments (p < 0.05). In ZIR, only the BJ protocol increased roughness (p = 0.001). In conclusion, dental prophylaxis protocols do not significantly affect the mechanical strength of RC, LD, and ZIR materials, thus allowing any protocol to be used for these materials. However, for LEU ceramics, the BJ protocol should be avoided due to its effect of reducing fatigue strength and damaging the surface. Full article

This study investigates the mechanical properties and biocompatibility of eight commercially available filaments tailored for Fused Deposition Modeling (FDM) additive manufacturing. Test specimens were fabricated using original PRUSA MK4 printers, with ten samples from each selected polymer. Mechanical evaluations through static tensile and three-point bending tests revealed that PETG Carbon and PA+15CF exhibited superior tensile and flexural strengths, making them highly suitable for applications requiring high mechanical resilience. Biocompatibility assessments in line with the ISO 10993-5:2009 and ISO 10993-12:2021 standards indicated that all materials except FiberFlex 40D Fiberlogy were non-cytotoxic, supporting their potential in biomedical applications. The experimental data established material constants within the Johnson–Cook strength model, which effectively predicted the mechanical behaviors of monotonic materials like FiberFlex 40D, PETG, HIPS, TPU, and PA+15CF Rosa 3D, with maximum fitting errors not exceeding 2.6%. However, the model was inadequate for non-monotonic materials like PLA and PETG, resulting in higher errors and less accurate simulations. Scanning electron microscope (SEM) analyses provided insights into fracture mechanisms, correlating fracture surface characteristics with mechanical performance. This comprehensive study advances the understanding of mechanical properties in thermoplastic materials for 3D printing, validates numerical models for certain materials, and confirms material suitability for biomedical use. Full article

Concrete structures such as bridge decks and road pavements are subjected to repetitive loading and are susceptible to fatigue failure. A simplified stress–strain analysis method that can simulate concrete behavior with a sound physical basis, acceptable prediction precision, and reasonable computation cost is urgently needed to address the critical issue of high-cycle fatigue in structural engineering. An equivalent fatigue constitutive model at discrete loading cycles incorporated into the concrete damaged plasticity model (CDPM) in Abaqus is proposed based on fatigue damage evolution. A damage variable is constructed from maximum fatigue strains, and fatigue damage evolution is described by a general equation whose parameters’ physical meaning and value range are identified. With the descending branch of the monotonic stress–strain curve as the envelope of fatigue residual strength and fatigue damage evolution equation as shape function, fatigue residual strength, residual stiffness, and residual strain are calculated. The equivalent fatigue constitutive model is validated through comparison with experimental data, where satisfactory simulation results were obtained for axial compression and flexural tension fatigue. The model’s novelty lies in integrating the fatigue damage evolution equation with CDPM, explicitly explaining performance degradation caused by fatigue damage. The proposed model could accommodate various forms of concrete constitution and fatigue stress states and has a broad application prospect for fatigue analysis of concrete structures. Full article

SiC-fiber-reinforced Al-Mg matrix composites with different mass fractions of Mg were fabricated by combining colloidal dispersion with a squeeze melt infiltration process. The microstructure, mechanical and damping properties, and the corresponding mechanisms were investigated. Microstructure analyses found that SiC_f/Al-Mg composites presented a homogeneous distribution of SiC fibers, and the relative density was higher than 97% when the mass fraction of Mg was less than 20%; the fiber–matrix interface bonded well, and no obvious reaction occurred at the interface. The SiC_f/Al-10Mg composite exhibited the best flexural strength (372 MPa) and elastic modulus (161.7 GPa). The fracture strain of the composites decreased with an increase in the mass fraction of Mg. This could be attributed to the strengthened interfacial bonding due to the introduction of Mg. The damping capacity at RT increased dramatically with an increase in the strain when the strain amplitude was higher than 0.001%, which was better than the alloys with similar composition, demonstrating a positive effect of the SiC fiber on improving the damping capacity of composite; the damping capacity at a temperature beyond 200 °C indicated a monotonic increase tendency with the testing temperature. This could be attributed to the second phase, which formed more strong pinning points and increased the dislocation energy needed to break away from the strong pinning points. Full article

This study aimed to evaluate the static response of prestressed reinforced concrete beams strengthened in their flexure and shear properties using different strengthening techniques, steel plates, and externally bonded woven carbon fiber fabric (WCFF). The experimental work involved testing twenty large-scale prestressed reinforced concrete beams with a length of 3000 mm, and cross-sections measuring 400 mm in height and 200 mm in breadth were cast in the factory and tested in the laboratory. Four beams without prestressing served as the reference beams; two unbonded pre-tensioned beams served as the control beams, and the remaining fourteen beams were strengthened with steel plates and externally bonded woven carbon fiber fabric (WCFF). Eight of the beams were strengthened with 4 mm thick steel plates and tested under a monotonically increasing load with manual readings recorded. The remaining six beams were strengthened with 0.5 mm thick WCFF and tested under a monotonically increasing load with manual readings recorded. The variables considered included the strengthening techniques (FRP composite sheets, steel plates), the types of strengthening (slices, U-shaped), and the flexural and shear capacities of the strengthened beams. All the implemented strengthening techniques yielded enhancements in both the flexural and shear strength outcomes of the beams compared to their respective controls. The most significant increase in load capacity, whether in terms of ultimate load or first crack load, for the prestressed concrete beams’ flexure properties occurred when strengthening with U-shaped steel plates. Additionally, the greatest reduction in deflection at the point of reaching the maximum load for the prestressed concrete beams, in terms of their flexure properties, was observed when strengthening with U-shaped steel plates. Similarly, the maximum load increase for the prestressed concrete beams, in terms of their shear properties, was achieved through strengthening with U-shaped woven carbon fiber fabric wrapping. Furthermore, a finite element model was created to simulate various experimental specimens. The finite element model’s results exhibited harmony with the experimental results, affirming the efficacy of the presented finite element model. Full article

This paper aims to determine the effects of local corrosion at three different corrosion areas, the (1) entire area, (2) the constant moment area, and (3) the constant shear area, on the flexural performance of RC beams. To analyze this, an experimental study was carried out to prepare two series of RC beams (200 × 300 × 2800 mm) created with three different degrees of corrosion, inducing local rebar corrosion. Furthermore, two series of experimental tests were conducted under different loading types: monotonic and cyclic loading. It was observed that the strength capacity reduction grew in the RC specimens with induced corrosion in the order of the (1) entire area > (2) the constant moment area > (3) the constant shear area, as the average corrosion rate increased. Our test results further showed that the yield and ultimate strength were kept nearly equivalent to the uncorroded RC specimen, with average corrosion rates of 10% and 15%, respectively. Over these corrosion rates, the yield strength and ultimate strength dropped significantly. Compared to the test results under a monotonic loading condition, the structural capacity under a cyclic loading condition decreased, with a more pronounced tendency for each corrosion case as the corrosion rate increased. Longitudinal cracks developed throughout and adjacent to the corrosion areas as the corrosion rate increased. Thus, we can infer that strength reductions may be strongly influenced by these longitudinal cracks. Full article

In this study, an experimental program was developed to investigate the flexural behavior of pre-damaged reinforced concrete (RC) beams that had been repaired and strengthened using carbon fiber-reinforced polymer (CFRP) laminates under a monotonic load. Two techniques were used: externally bonded reinforcement (EBR) and near-surface-mounted (NSM) reinforcement, to repair and strengthen the tested beams. The experimental program involved casting and testing nine simply supported RC rectangular beams; one beam was considered as the reference beam and did not undergo additional strengthening, and the remaining beams were strengthened using CFRP laminates. These eight beams were divided into two main groups for the purposes of strengthening: beams for which the EBR technique was used, and beams for which the NSM technique was used. The primary variables observed in the EBR and NSM groups included four damage percentages obtained according to the preload (20, 40, 60, and 80%) from the ultimate load carried by the reference beam. The experimental results show that decreasing the damage percentage leads to an increase in ultimate strength from about 3.6% to 17.2% for the beams repaired using the EBR technique and from 27.6% to 57% for the beams repaired using the NSM technique; additionally, the NSM method was more effective than the EBR method in terms of the flexural strength and mode of failure. However, using CFRP laminates enhances the flexure capacity of strengthened RC beams. Full article

The present research focused on studying the mechanical properties of three commercially available thermoplastic-based materials used for the additive manufacturing (AM) fused filament deposition (FFD) method. The scientific motivation for the study was the limited information available in the literature regarding the materials’ properties, the inconsistencies that were recorded by other scientists between the materials’ properties and the technical datasheets and the anisotropic behavior of additively manufactured materials. Thereby, it was considered of great importance to perform an extensive study on several materials’ mechanical properties, such as tensile properties and flexural properties. Three materials were tested, Tough PLA, nGen CF10 and UltraFuse PAHT CF15. The tests consisted of monotonic tensile tests, open-hole tensile tests and three-point bending tests. The tests were assisted also with the use of microscopical investigations. Framed specimens’ configurations with two different raster orientations (90°/0° and −45°/+45°) were manufactured using an in-house-developed 3D printing equipment. The best mechanical performances were recorded for UltraFuse PAHT CF15. The 90°/0° raster orientations ensured the highest tensile, open-hole tensile and flexural strength, regardless of the material type, while the −45°/+45° raster orientations ensured the highest elongation values. The analysis showed the importance of the experimental validation of materials for AM. Full article

In this study, a series of composites comprising polyether ether ketone (PEEK) and carbon fiber (CF)-reinforced polybenzoxazine for high-temperature friction materials for vehicle brake applications were developed using a high-temperature compression molding technique. The objective of this research was to systematically investigate the thermal, mechanical (tensile and flexural), and tribological performance of friction materials made from polybenzoxazine-based composites by varying the PEEK/CF mass ratio. Our study reveals the substantial improvement effect of the increased content of PEEK fibers on the thermal conductivity, the coefficient of friction, and the friction strength of the polybenzoxazine-based composite materials. Meanwhile, the introduction of carbon fibers was found to have a monotonic positive effect on the mechanical (tensile and flexural) properties and wear performance of the polybenzoxazine-based composites. The polybenzoxazine-based composites exhibit high mechanical strength, with a tensile strength of 50.1–78.6 MPa, Young’s modulus of 10.2–24.3 GPa, a flexural strength of 62.1–88.3 MPa, and a flexural modulus of 13.1–27.4 GPa. In addition, the polybenzoxazine-based composite with a PEEK/CF mass ratio of 75:25 exhibits a high and stable coefficient of friction (0.33) and a specific wear rate (1.79 × 10⁻⁷ cm³/Nm at room temperature). Subsequent to the wear test at ambient temperature, the worn surfaces of five polybenzoxazine-based composite samples with various PEEK/CF mass ratios were studied using electron microscopy technology (SEM). The observation of small cracks and tiny grooves on the worn surfaces indicates a combined abrasive and adhesive wear mechanism of the material. Our experimental results clearly reveal superior mechanical properties and excellent tribological characteristics. As a result, these composites show promising potential for the application of friction materials in terms of vehicle braking system applications. Full article

Ultrasonic pulse velocity (UPV) is a non-destructive measurement technique with which the quality of any concrete element can be evaluated. It provides information on concrete health and for assessing the need for repair in a straightforward manner. In this paper, the relationship is studied between UPV readings and the mechanical behavior of self-compacting concrete (SCC) containing coarse, fine, and/or powdery RA. To do so, correlations and simple- and multiple-regression relationships between compressive strength, modulus of elasticity, splitting tensile strength, flexural strength, and UPV readings of nine SCC mixes were assessed. The correlations showed that the relationship of UPV with any mechanical property was fundamentally monotonic. The inverse square-root model was therefore the best-fitting simple-regression model for all the mechanical properties, although for bending-tensile-behavior-related properties (splitting tensile strength and flexural strength) the estimation accuracy was much lower than for compressive-behavior-related properties (compressive strength and modulus of elasticity). Linear-combination multiple-regression models showed that the properties related to bending-tensile behavior had a minimal influence on the UPV value, and that their introduction resulted in a decreased estimation accuracy. Thus, the multiple-regression models with the best fits were those that linked the compressive-behavior-related properties to the UPV readings. This therefore enables the estimation of the modulus of elasticity when the UPV and compressive strength are known with a deviation of less than ±20% in 87% of the SCC mixes reported in other studies available in the literature. Full article