Search Results (245)

High strength and high ductility concrete (HSHDC) exhibit exceptional compressive strength (up to 90 MPa) and remarkable tensile ductility (ultimate tensile strain reaching 6%), making them highly resilient under impact loading. To elucidate the influence of strain rate and wet–dry cycling of salt spray on the dynamic compressive response of HSHDC, a series of tests was conducted using a 75 mm split Hopkinson pressure bar (SHPB) system on specimens exposed to cyclic corrosion for periods ranging from 0 to 180 days. The alternating seasonal corrosion environment was reproduced by using a programmable walk-in environmental chamber. Subsequently, both uniaxial compression and SHPB tests were employed to evaluate the post-corrosion dynamic compressive properties of HSHDC. Experimental findings reveal that corrosive exposure significantly alters both the static and dynamic compressive mechanical behavior and constitutive characteristics of HSHDC, warranting careful consideration in long-term structural integrity assessments. As corrosion duration increases, the quasi-static and dynamic compressive strengths of HSHDC exhibit an initial enhancement followed by a gradual decline, with stress reaching its peak at 120 days of corrosion under all strain rates. All specimens demonstrated pronounced strain-rate sensitivity, with the dynamic increase factor (DIF) being minimally influenced by the extent of corrosion under dynamic strain rates (112.6–272.0 s⁻¹). Furthermore, the peak energy-consumption capacity of HSHDC was modulated by both the duration of corrosion and the applied strain rate. Full article

Polypropylene fiber, as a micro-scale reinforcement material, has been widely recognized for its ability to effectively inhibit crack propagation during the service life of concrete, thereby enhancing both its crack resistance and durability. This study presents an experimental investigation of the mechanical properties of polypropylene fiber-reinforced concrete specimens. The primary objective of this study was to assess the influence of varying fiber lengths and volumetric fiber contents on the load-bearing behavior of concrete. Seven sets of concrete specimens with different polypropylene fiber parameters (dosage and length) were prepared and subjected to a series of tests, including compressive strength, splitting tensile strength, flexural strength, and axial compressive stress–strain behavior. Specifically, coarse polypropylene fibers with two lengths (30 mm and 50 mm) and three dosages (0.5%, 1%, and 1.5%) were investigated. Experimental results facilitated the identification of the optimal fiber dosage and length at which the mechanical properties of the concrete specimens were maximized. Subsequently, a constitutive model for polypropylene fiber-reinforced concrete was established. The analysis elucidated the relationships between the parameters within the constitutive model, axial compressive strength of the concrete, and characteristic fiber parameters. The derived formulations provide a theoretical foundation for subsequent finite element analyses of polypropylene-fiber-reinforced concrete. Full article

Three-dimensional concrete printing (3DCP) is an emerging additive manufacturing technology with increasing application potential in the construction industry, offering advantages such as reduced labor requirements, shortened construction time, and material efficiency. However, structural integrity remains a challenge, particularly due to weak interlayer bonding resulting from the layered manufacturing process. This study investigates the mechanical performance and anisotropy of 3D-printed mineral-based composites with respect to the time interval between successive layers. Specimens were printed with varying interlayer intervals (0, 25, and 50 min) and tested in different loading directions. Flexural, compressive, and tensile strengths (direct and splitting methods) were measured both parallel and perpendicular to the layer orientation. Results showed a clear degradation in mechanical properties with increasing interlayer time, particularly in the direction perpendicular to the layers. Flexural strength decreased by over 25% and direct tensile strength by up to 40% with a 25 min interval. Compressive strength also declined, though less dramatically. Compared to cast specimens, printed elements showed 3–4 times lower compressive strength, highlighting the significant impact of interlayer cohesion. This study confirms that both the time between layers and the loading direction strongly influence mechanical behavior, underlining the anisotropic nature of 3DCP elements and the need for process optimization to ensure structural reliability. Full article

The present work aims to study the effect of cyclic loading on the tensile behavior of a chemically stabilized sandy soil, whether or not reinforced with polypropylene or sisal fibers. To this end, a series of splitting tensile strength tests were carried out by varying the frequency of the cyclic loading. During cyclic loading a substantial decrease in accumulated plastic axial displacement was observed with rising frequency when fibers were incorporated. On average, the reduction was 28% for polypropylene fibers and 14% for sisal fibers. For the polypropylene fibers, this effect is more pronounced because of a greater number of randomly distributed fibers, creating a strong and dense interlocking network. Regarding the load-displacement characteristics, fiber inclusion leads to a more ductile tensile response, which is identified by a secondary peak strength and residual strength. The cyclic loading frequency does not show a distinct trend concerning the post-cyclic tensile strength behavior; this behavior is dependent on the mechanical properties of materials (cemented matrix and fibers). Nevertheless, the cyclic stage resulted in an increased post-cyclic tensile strength for sisal fibers (ranging from 23% to 51%), although no clear trend was observed with respect to frequency variation. In contrast, for polypropylene fibers, the cyclic stage resulted in a more ductile tensile mechanical response, with post-cyclic tensile strength increasing from 1% to 16% as the frequency decreased. Full article

Reinforced concrete (RC) deep beams constructed with low-strength concrete are susceptible to sudden splitting failures in the strut region due to shear–compression stresses. To mitigate this vulnerability, various strengthening techniques, including steel plates, fiber-reinforced polymer sheets, and cementitious composites, have been explored to confine the strut area. This study investigates the structural performance of RC deep beams with low-strength concrete, strengthened externally using an Engineered Cementitious Composite (ECC) layer. To ensure effective confinement and uniform shear distribution, shear reinforcement was provided at equal intervals with configurations of zero, one, and two vertical shear reinforcements. Four-point bending tests revealed that the ECC layer significantly enhanced the shear capacity, increasing load-carrying capacity by 51.6%, 54.7%, and 46.7% for beams with zero, one, and two shear reinforcements, respectively. Failure analysis through non-linear finite element modeling corroborated experimental observations, confirming shear–compression failure characterized by damage in the concrete struts. The strut-and-tie method, modified to incorporate the tensile strength of ECC and shear reinforcement actual stress values taken from the FE analysis, was used to predict the shear capacity. The predicted values were within 10% of the experimental results, underscoring the reliability of the analytical approach. Overall, this study demonstrates the effectiveness of ECC in improving shear performance and mitigating strut failure in RC deep beams made with low-strength concrete. Full article

Aramid fibre has become a critical material for individual soft body armour due to its lightweight nature and exceptional impact resistance. To investigate its energy absorption mechanism, quasi-static and dynamic tensile experiments were conducted on Kevlar^® 29 plain-woven fabric using a universal material testing machine and a Split Hopkinson Tensile Bar (SHTB) apparatus. Tensile mechanical responses were obtained under various strain rates. Fracture morphology was characterised using scanning electron microscopy (SEM) and ultra-depth three-dimensional microscopy, followed by an analysis of microstructural damage patterns. Considering the strain rate effect, a viscoelastic constitutive model was developed. The results indicate that the tensile mechanical properties of Kevlar^® 29 plain-woven fabric are strain-rate dependent. Tensile strength, elastic modulus, and toughness increase with strain rate, whereas fracture strain decreases. Under quasi-static loading, the fracture surface exhibits plastic flow, with slight axial splitting and tapered fibre ends, indicating ductile failure. In contrast, dynamic loading leads to pronounced axial splitting with reduced split depth, simultaneous rupture of fibre skin and core layers, and fibrillation phenomena, suggesting brittle fracture characteristics. The modified three-element viscoelastic constitutive model effectively captures the strain-rate effect and accurately describes the tensile behaviour of the plain-woven fabric across different strain rates. These findings provide valuable data support for research on ballistic mechanisms and the performance optimisation of protective materials. Full article

This work aims to reveal the full-field strain evolution characteristics and failure mechanisms of anisotropic coal samples under creep loading. A series of compression tests combined with digital image correlation (DIC) monitoring were employed to characterize the strain evolution process of coal specimens with bedding angles of 0°, 30°, 60°, and 90°. Testing results show that the peak strength, peak strain, and the creep loading stage of coal are significantly influenced by the bedding angle. The peak strength initially decreases and then increases as the bedding angle increases. In addition, the creep failure of coal manifests as a process of instantaneous deformation, decelerating creep, steady-state creep, accelerating creep, and failure. Under graded creep loading conditions, coal specimens exhibit distinct creep characteristics at high stress levels. Moreover, the bedding angle significantly influences the strain field evolution of the coal samples. Finally, for coal specimens with bedding angles of 0° and 90°, the final macroscopic fracture pattern upon failure is characterized by longitudinal tensile splitting. In contrast, coal samples with bedding angles of 30° and 60° tend to exhibit failure along the bedding interfaces, forming tensile-shear fractures. The results of this study will provide theoretical guidance for the prevention, early warning, and safety management of coal mine disasters. Full article

As 3D concrete printing emerges as a transformative construction method, its structural safety remains hindered by unresolved issues of mechanical anisotropy and interlayer defects. To address this, we systematically investigate the failure mechanisms and mechanical performance of basalt fiber-reinforced 3D-printed magnesite concrete. A total of 30 cube specimens (50 mm × 50 mm × 50 mm)—comprising three types (Corner, Stripe, and R-a-p)—were fabricated and tested under compressive and splitting tensile loading along three orthogonal directions using a 2000 kN electro-hydraulic testing machine. The results indicate that 3D-printed concrete exhibits significantly lower strength than cast-in-place concrete, which is attributed to weak interfacial bonds and interlayer pores. Notably, the R-a-p specimen’s Z-direction compressive strength is 38.7% lower than its Y-direction counterpart. To complement the mechanical tests, DIC, CT scanning, and SEM analyses were conducted to explore crack development, internal defect morphology, and microstructure. A finite element model based on the experimental data successfully reproduced the observed failure processes. This study not only enhances our understanding of anisotropic behavior in 3D-printed concrete but also offers practical insights for print-path optimization and sustainable structural design. Full article

This study presents an innovative solution to improve the mechanical performance of traditional cemented tailings backfill (CTB) by incorporating 3D-printed polymer lattice (3DPPL) reinforcements. We systematically investigated three distinct 3DPPL configurations (four-column FC, six-column SC, and cross-shaped CO) through comprehensive experimental methods including Brazilian splitting tests, digital image correlation (DIC), and scanning electron microscopy (SEM). The results show that the 3DPPL reinforcement significantly enhances the CTB’s tensile properties, with the CO structure demonstrating the most substantial improvement—increasing the tensile strength by 85.6% (to 0.386 MPa) at a cement-to-tailings ratio of 1:8. The 3DPPL-modified CTB exhibited superior ductility and progressive failure characteristics, as evidenced by multi-stage load-deflection behavior and a significantly higher strain capacity (41.698–51.765%) compared to unreinforced specimens (2.504–4.841%). The reinforcement mechanism involved synergistic effects of macroscopic truss behavior and microscopic interfacial bonding, which effectively redistributed the stress and dissipated energy. This multi-scale approach successfully transforms CTB’s failure mode from brittle to progressive while optimizing both strength and toughness, providing a promising advancement for mine backfill material design. Full article

This paper proposes a steel-ECC ordinary concrete composite continuous bridge deck structure to address the cracking problem of simply supported beam bridge deck continuity. Through theoretical and experimental research, a high-performance ECC material was developed. The ECC material has a compressive strength of 57.58 MPa, a tensile strain capacity of 4.44%, and significantly enhanced bending deformation ability. Bonding tests showed that the bond strength of the ECC-reinforcing bar interface reaches 22.84 MPa when the anchorage length is 5d, and the splitting strength of the ECC-concrete interface is 3.58 MPa after 4–5 mm chipping treatment, with clear water moistening being the optimal interface treatment method. Full-scale tests indicated that under 1.5 times the design load, the crack width of the ECC bridge deck continuity structure is ≤0.12 mm, the maximum deflection is only 5.345 mm, and the interface slip is reduced by 42%, achieving a unified control of multiple cracks and coordinated deformation. The research results provide a new material system and interface design standards for seamless bridge design. Full article

Geopolymer concrete (GPC) offers reduced carbon emissions and employs industrial by-products such as fly ash and ground granulated blast furnace slag (GGBFS). In this study, the synergistic augmentation of shear carrying capacity in steel-fiber-reinforced rubberized geopolymer concrete (FRGC) incorporating industrial by-products such as fly ash, GGBFS, and recycled rubber for sustainable construction is investigated. The reinforced rubberized geopolymer concrete (RFRGC) mixtures contained 20% rubber crumbs as a partial replacement for fine aggregate, uniform binder, and alkaline activator. The findings revealed that 1.25% steel fiber achieved optimal hardened properties (compressive strength, flexural, and split tensile strength), with 12 M sodium hydroxide and oven curing achieving maximum values. An increase in molarity improved geopolymerization, with denser matrices, while oven curing boosted polymerization, enhancing the bonding between the matrix and the fiber. The effect of steel fiber on the shear carrying capacity of RFRGC beams without stirrups is also discussed in this paper. An increased fiber content led to an increased shear carrying capacity, characterized by an improvement in first crack load and a delayed ultimate failure. These results contribute to sustainable concrete technologies for specifically designed FRGC systems that can balance structural toughness, providing viable alternatives to traditional concrete without compromising strength capacity. Full article

In this study, bamboo fiber bundles were directly extracted from raw bamboo material to fabricate reconstituted bamboo using the traditional hot-pressing method. The tensile behaviors and failure mechanisms of both the bamboo fiber bundle and its bamboo scrimber under various strain rates (quasi-static, 350/s, 950/s and 1700/s) were investigated by the SHTB system (split-Hopkinson tensile bar, high-speed camera and digital image correlation method). The results showed that the bamboo scrimber exhibited an obvious positive strain rate effect. The ultimate tensile strength of the bamboo scrimber at a strain rate of 1700/s was close to 200 MPa, but it was only about 80 MPa under quasi-static loading. This experimental result was further validated by the tensile behaviors of single bamboo fiber bundles at different strain rates (quasi-static, 300/s, 700/s and 1500/s). In addition, as the strain rate increased, the fracture surface of the bamboo changed from a linear shape to a discontinuous folded shape. Full article

Geopolymer recycled aggregate concrete (GRAC) is an eco-friendly material utilizing industrial byproducts (slag, fly ash) and substituting natural aggregates with recycled aggregates (RA). Incorporating steel-polypropylene hybrid fibers into GRAC to produce hybrid-fiber-reinforced geopolymer recycled aggregate concrete (HFRGRAC) can bridge cracks across multi-scales and multi-levels to synergistically improve its mechanical properties. This paper aims to investigate the mechanical properties of HFRGRAC with the parameters of steel fiber (SF) volume fraction (0%, 0.5%, 1%, 1.5%) and aspect ratio (40, 60, 80), polypropylene fiber (PF) volume fraction (0%, 0.05%, 0.1%, 0.15%), and RA substitution rate (0%, 25%, 50%, 75%, 100%) considered. Twenty groups of HFRGRAC specimens were designed and fabricated to evaluate the compressive splitting tensile strengths and flexural behavior emphasizing failure pattern, load–deflection curve, and toughness. The results indicated that adding SF enhances the specimen ductility, mechanical strength, and flexural toughness, with improvements proportional to SF content and aspect ratio. In contrast, a higher percentage of RA substitution increased fine cracks and reduced mechanical performance. Moreover, the inclusion of PF causes cracks to exhibit a jagged profile while slightly improving the concrete strength. The significant synergistic effect of SF and PF on mechanical properties of GRAC is observed, with SF playing a dominant role due to its high elasticity and crack-bridging capacity. However, the hydrophilic nature of SF combined with the hydrophobic property of PF weakens the bonding of the fiber–matrix interface, which degrades the concrete mechanical properties to some extent. Full article

Recycled aggregate concrete (RAC) holds significant promise for reducing the environmental impact of the construction industry. However, the poor mechanical properties of RAC compared to conventional concrete are mainly due to the porous and soft nature of recycled aggregates. While fiber reinforcement has been proposed as a promising method to address this issue, existing studies primarily focus on steel and polypropylene fibers, with limited systematic comparison of alternative fiber types and dosages. In particular, the mechanical enhancement mechanisms of basalt and glass fibers in RAC remain underexplored, and there is a lack of predictive models for strength behavior. This study evaluates the effects of basalt and glass fibers on RAC through uniaxial compression, splitting tensile, and three-point bending tests. Nine mixtures with varying fiber types and volume fractions (1.0–2.5%) were tested, and results were compared to plain RAC. Key properties such as strength, energy absorption, toughness, and flexibility were analyzed using load–displacement curves and advanced toughness indices. Both fiber types improved tensile and flexural properties, with glass fibers showing superior performance, particularly at 1.5% content, where the splitting tensile strength increased by up to 40% and the flexural strength improved by 42.19%. Basalt fibers dispersed more uniformly but were less effective in enhancing toughness and crack resistance. Excessive fiber content reduced matrix homogeneity and mechanical performance. Optimal fiber dosages were identified as 1–1.5% for glass fibers and 1–2% for basalt fibers, depending on the targeted property. Predictive formulas for the flexural strength of fiber-reinforced RAC are also proposed, offering guidance for the design of structural RAC elements. Full article

Fractures and voids are widely distributed in slope rock masses. These defects promote crack initiation and propagation, ultimately leading to rock mass failure. Investigating their damage evolution mechanisms and strength characteristics is of significant importance for slope hazard prevention. A numerical simulation study of Brazilian splitting tests on disk samples containing prefabricated holes and fractures was conducted using the Finite Element Method with Cohesive Zone Modeling (FEM-CZM) in ABAQUS by embedding zero-thickness cohesive elements within the finite element model. This 2021 study analyzed the effects of fracture angle and length on tensile strength and crack propagation characteristics. The results revealed that when the fracture angle is small, cracks initiate near the fracture and propagate and intersect radially as the load increases, ultimately leading to specimen failure, with the crack coalescence pattern exhibiting local closure. As the fracture angle increases, the initiation location of the crack shifts. With an increase in fracture length, the crack initiation position may transfer to other parts of the fracture or near the hole, and longer fractures may result in more complex coalescence patterns and local closure phenomena. During the tensile and stable failure stages, the load–displacement curves of samples with different fracture angles and lengths exhibit similar trends. However, the fracture angle has a notable impact on the curve during the shear failure stage, while the fracture length significantly affects the peak value of the curve. Furthermore, as displacement increases, the proportion of tensile failure undergoes a process of rapid decline, slow rise, and then rapid decline again before stabilizing, with the fracture angle having a significant influence on the proportion of tensile failure. Lastly, as the fracture angle and length increase, the number of damaged cohesive elements shows an upward trend. This study provides novel perspectives on the tensile behavior of fractured rock masses through the FEM-CZM approach, contributing to a fundamental understanding of the strength characteristics and crack initiation mechanism of rocks under tensile loading conditions. Full article