Three-point Bending Beam Research Articles

Low-temperature flexural tensile performance degradation of asphalt mixture under coupled UV radiation and freeze-thaw cycles

The Qinghai-Tibetan Plateau in China experiences extreme climatic conditions, including intense ultraviolet (UV) radiation, frequent freeze-thaw cycles (FTCs). This study aims to investigate the degradation of low-temperature flexural tensile performance in asphalt mixtures subjected to UV radiation, FTCs, their coupled effects. An alternating two-factor laboratory procedure was designed to simulate these conditions, and three-point bending beam tests were conducted on asphalt mixture beams after exposure to various durations of UV radiation and FTCs. A comprehensive multi-indicator approach was employed to assess the performance degradation. The results revealed that UV radiation primarily reduced the low-temperature flexural tensile strain of asphalt mixtures, while FTCs mainly weakened the tensile strength. FTCs were the predominant factor in performance degradation. Their coupling effects resulted in a pronounced mutual enhancement of damage, with damage variables increment value under coupled conditions being more than seven times greater than those in the control group.

Design Method of Gyroid Lattice Structure Based on the Load Paths Direction and Capacity

The Design of lattice structures with triply periodic minimal surface (TPMS) can improve the specific stiffness, strength, heat dissipation, and energy absorption functions of their physical structures. The load-transferred law in the structure can serve as a crucial basis for the design, including the distribution and anisotropy of the unit cells. In this paper, a design method based on load paths is proposed and a series of Gyroid lattice structures with variable density cells, variable direction cells, and combination of variable density and direction cells, are designed with better mechanical properties. The load paths within a given structure are extracted to explicitly provide the load-transferred law. The capacity of the load paths is then proposed to guide the distribution of the cells, and a mapping relationship with the parameters controlling the porosity is established. The lattice structures with variable density cells are designed. Afterwards, the pointing stress vectors of the load paths is defined as the main load-transferred direction in the local region to guide the direction of the cells. Based on the anisotropic behavior of the Gyroid cells, the direction setting principles are formulated, and the lattice structures with variable direction cells are designed. Furthermore, a model generation method is proposed, and the Gyroid lattice structures that combine variable density and direction cells are implemented. Two models are applied to validate the proposed method, including a two-dimensional three-point bending beam and a three-dimensional supporting beam. The obtained results show that for the same porosity, both the variable density and variable direction designs of Gyroid cells allow to improve the mechanical properties. The variable density design outperforms the variable direction design. In addition, the Gyroid lattice structures combining variable density and direction cells have significantly higher performance, which indicates that the proposed design method can more effectively increase the load-bearing performance.

Cracking performance characterisation of aramid fiber-reinforced asphalt mixtures using digital image correlation

ABSTRACT Conventional index-based testing of asphalt mixtures cannot accurately capture local deformation in a sample, limiting the usage of standard test measurements. The non-contact-based measurements proved effective to capture local deformation fields. This study aimed to capture the fatigue and thermal cracking behaviour of fiber-reinforced asphalt mixture (FRAM) by utilising digital image correlation (DIC). One binder (PG76-22), a diabase aggregate and three fibers (polyolefin/ aramid fibers (PFA) at 0.05% dosage and Sasobit-coated aramid fibers at 0.01% and 0.02% dosage) were used to prepare a total of four mixtures (one control and three FRAM). All these mixtures were produced at a local batch plant following manufacturer-recommended mixing methods. DIC analysis was performed for three-point bending beam (3PB) and disk shape compact tension (DCT) tests at intermediate temperature (25°C) and low temperatures of −12°C and −18°C. Based on index values from DCT and 3PB, the thermal and fatigue cracking performance enhancement was not significant. However, DIC analysis showed that, regardless of testing temperature, the crack propagated in a random pattern for FRAM, whereas the crack followed a relatively straight path for the control mix. Finally, based on DIC strain contours, FRAM mixtures exhibit distributed strain over a larger area compared to the control mix.

Stochastic Extension of Nonlocal Macro–Mesoscale Consistent Damage Model for Fracture Behaviors of Concrete Materials

The nonlinearity and randomness in composite materials such as concrete present challenges regarding the safety analysis and reliability-based design of structures. Based on two-scale damage evolution and physically based geometry–energy conversion, the nonlocal macro–mesoscale consistent damage model (NMMD) shows a unique capability in dealing with the nonlinearity of crack evolution. In this paper, a stochastic extension of the NMMD model is proposed to analyze the stochastic fracture behaviors of concrete materials. The extended model uses the stochastic harmonic function (second kind) to represent the spatial variability in concrete properties and thus to investigate the influence of inhomogeneity in the cracking process. Numerical examples of three-point bending beams without defects and with initial cracks of various sizes demonstrate that the stochastic NMMD model is capable of not only capturing uncertain fluctuations in peak load but also simulating the random walk of the crack path with the instantaneous transition of fracture modes, as observed in experiments. In addition, the effectiveness of the stochastic NMMD model with only a single random field (i.e., Young’s modulus) also contradicts the conventional assertion that stochastic simulations of quasi-brittle fracture should contain at least two mechanical properties with spatial randomness. Finally, the investigation of fracture energy with stochastic fluctuations reveals that randomness resulting from heterogeneity can statistically improve the fracture toughness of concrete materials to some extent.

Mixed FEM implementation of three-point bending of the beam with an edge crack within strain gradient elasticity theory

This paper considers the problem of symmetrical three-point bending of a prismatic beam with an edge crack. The solution is obtained by the mixed finite element method within the simplified Toupin–Mindlin strain gradient elasticity theory. A mixed variational formulation of the boundary value problem for displacements–strains–stresses and their gradients is applied, simplifying the choice of approximating functions. The concept of energy balance is adopted to calculate the energy release rate with a virtual increase in crack length. The increment of the potential energy of an elastic body is determined by accounting for the strain and stress gradient contribution. Numerical calculations were performed using a quasi-uniform triangular mesh of the cross-type. The mesh refinement was applied in the vicinity of the crack tip, at the concentrated support, and the point of application of the transverse force, and uniform mesh partitioning was utilized in the rest of the beam. The fine-mesh analysis was carried out on the successively condensed meshes in the stress concentration domain for different values of the length scale parameter. The crack opening displacements and the distribution of strains and Cauchy stresses for various values of the length scale parameter are presented. An increase in this parameter increases the stiffness of the crack, which leads to a decrease in the crack opening displacements and a smooth closure of its faces at the crack tip. In addition, accounting for the scale parameter reduces the calculated values of strains and stresses near the crack tip. Based on the energy balance criterion, local fracture parameters such as the release rate of elastic energy at the crack tip and the stress intensity factor are determined for different values of the mesh step. The numerical calculations indicate the convergence of the obtained approximations. The main feature of solutions, which includes the strain gradient contribution, is the decrease in the values of the calculated parameters associated with the fracture energy compared to the classical elasticity theory.

Improved fracture toughness evaluation for fiber-reinforced asphalt concrete through double-parameter theory

Fracture toughness serves as a key parameter in the design and durability assessment of asphalt concrete. Quantifying the fracture toughness for fiber-reinforced asphalt concrete (FRAC), remains challenging due to the incorporation of fibers. This study proposes an improved method for evaluating the fracture toughness of FRAC, based on the double-parameter theory derived from the theoretical concepts of stress intensity factor K and energy release rate (double-K and double-G fracture models). Using Digital Image Correlation (DIC) technology, crack propagation during three-point bending beam tests on FRAC beams was measured, refining the calculation of critical crack length ac in the double-K fracture parameters. Additionally, a method is introduced to calculate the improved solution of double-G fracture parameters by monitoring crack propagation in real-time to determine the effective crack length a, and simultaneously computing the energy absorbed per unit crack extension, thereby constructing the J-R curve during stable crack growth phases. The fracture toughness of FRAC is evaluated by the improved method obtained double-G fracture parameters were used in Virtual Crack Closure Technique (VCCT) simulations to achieve virtual modeling of FRAC. The results demonstrate that the improved method provides accurate fracture performance indicators for FRAC. Moreover, the study establishes modified calculation formulas for (GICu) and (KICu) at unstable fracture toughness for FRAC at different temperatures, considering various fiber types and contents, thereby enhancing computational efficiency for practical applications. This research contributes to more accurate and effective methods for testing and evaluating the fracture performance of FRAC.

Characterisation of the Mechanical Properties of Natural Fibre Polypropylene Composites Manufactured with Automated Tape Placement

The integration of natural fibre thermoplastic composites, particularly those combining flax fibres with polypropylene, offers a promising alternative to traditional synthetic composites, emphasising sustainability in composite materials. This study investigates the mechanical properties of flax/polypropylene composites manufactured using flashlamp automated tape placement and press consolidation, individually and in combination. Tensile, compression, three-point bending, and double cantilever beam tests are utilised for comparing these manufacturing processes and the mechanical performance of the resulting composites. The microstructure of the tapes is investigated using cross-sectional microscopy, and the thermophysical behaviour is analysed utilising thermogravimetric analysis and differential scanning calorimetry. The temperature during placement is monitored using an infrared camera, and the pressure is mapped with pressure-sensitive films. The natural fibre tapes show a good aptitude for being manufactured with automated tape placement. The tensile performance of tapes manufactured with automated tape placement is close to that of press consolidated samples. Compression, flexural properties, and the mode I fracture toughness critical energy release rate all benefit from a second consolidation step.

Study on crack propagation behaviors of three-point bending concrete beams with small span-depth ratios

Three-point bending (TPB) beams with small span-depth ratios, i.e. TPB beams with the same span of 400 mm but various depths (100 mm, 150 mm and 200 mm), were tested to study the crack propagation behaviors of concrete. The evaluations of crack extension resistance curve (KR-curve), fracture process zone (FPZ) length, lFPZ, and crack tip opening displacement (CTOD) were studied. The digital image correlation (DIC) technique was utilized to monitor the entire loading process. Moreover, the effects of strain rates (10−5/s, 10−4/s, 10−3/s and 10−2/s) on the fracture process of TPB beams with small span-depth ratios (2, 2.5 and 3) were discussed based on findings in literature. The results shown that (1) with the increase of specimen depth from 100 mm to 200 mm, the obtained KR-curves and initial fracture toughness were not influenced by the small span-depth ratios, while different increase trends were observed for the unstable fracture toughness, the average maximum value of lFPZ and the value of CTOD. (2) With the loading rate increasing from 10−5/s to 10−2/s, the obtained KR-curve and the maximum length of FPZ increased slightly, while the evolution of CTOD was not affected by the loading rate.

Study on the dynamic fracture mechanical properties of ultra high-performance concrete under the influence of steel fiber content

Ultra-high performance concrete (UHPC) is characterized by its ultra-high strength and durability, making it suitable for use in large-span bridges, super high-rise buildings, and other special structures. These types of structures often have high requirements for crack control, making the exploration of UHPC's fracture mechanics properties of significant importance. Therefore, this paper sets up four steel fiber contents (0 %, 0.6 %, 1.2 % and 1.8 %) and four strain rates (10−5/s, 10−4/s, 10−3/s and 10−2/s), totaling 16 working conditions. The hydraulic servo system combined with digital image correlation (DIC) technology was used to conduct fracture mechanics tests on UHPC three-point bending beams. The test results show that the unstable fracture load of UHPC increases with the increase of strain rate and steel fiber content, and increasing the steel fiber content can enhance the strain rate effect of UHPC to a certain extent. Additionally, combined with the J-criterion model, this study proposed a dynamic criterion for the unstable fracture load of UHPC considering the influence of steel fiber content. The initial fracture toughness, unstable fracture toughness, and fracture energy of UHPC are significantly more affected by steel fiber content than by strain rate. Through DIC technology, the analysis of UHPC crack propagation shows that UHPC without steel fibers experiences rapid crack expansion in the Pre-90 % to Peak stage, with less influence from the strain rate. However, UHPC with steel fibers exhibits a more uniform crack growth rate, with the crack emergence phase gradually lagging as the strain rate increases. For UHPC without steel fibers, the crack opening displacement (COD) at the unstable fracture load point surges suddenly, while the COD development in UHPC with steel fibers is slower. At lower strain rates, an increase in steel fiber content leads to an earlier sudden increase phase in UHPC's COD; at higher strain rates, the influence of steel fiber content on the sudden increase phase of UHPC's COD is more scattered. The research results of this paper provide a theoretical basis for the calculation and analysis of the dynamic response of UHPC structures under seismic loads.

Effects of Mix Components on Fracture Properties of Seawater Volcanic Scoria Aggregate Concrete.

The fracture mechanism and macro-properties of SVSAC were studied using a novel test system combined with numerical simulations, which included three-point bending beam tests, the digital image correlation (DIC) technique, scanning electron microscopy (SEM), and ABAQUS analyses. In total, 9 groups and 36 specimens were fabricated by considering two critical parameters: initial notch-to-depth ratios (a0/h) and concrete mix components (seawater and volcanic scoria coarse aggregate (VSCA)). Changes in fracture parameters, such as the load-crack mouth opening displacement curve (P-CMOD), load-crack tip opening displacement curve (P-CTOD), and fracture energy (Gf), were obtained. The typical double-K fracture parameters (i.e., initial fracture toughness (KICini) and unstable fracture toughness (KICun)) and tension-softening (σ-CTOD) curve were analyzed. The test results showed that the initial cracking load (Pini), Gf, and characteristic length (Lch) of the SVSAC increased with decreasing a0/h. Compared with the ordinary concrete (OC) specimen, the P-CMOD and P-CTOD curves of the specimen changed after using seawater and VSCA. The evolution of the crack propagation length was obtained through the DIC technique, indicating cracks appeared earlier and the fracture properties of specimen decreased after using VSCA. Generally, the KICun and KICini of SVSAC were 36.17% and 8.55% lower than those of the OC specimen, respectively, whereas the effects of a0/h were negligible. The reductions in Pini, Gf, and Lch of the specimen using VSCA were 10.94%, 32.66%, and 60.39%, respectively; however, seawater efficiently decreased the negative effect of VSCA on the fracture before the cracking width approached 0.1 mm. Furthermore, the effects of specimen characteristics on the fracture mechanism were also studied through numerical simulations, indicating the size of the beam changed the fracture toughness. Finally, theoretical models of the double-K fracture toughness and the σ-CTOD relations were proposed, which could prompt their application in marine structures.

Fracture behavior and mechanical properties of engineered cementitious composites exposed to long-term sulfate and chloride environments

The fracture properties of engineered cementitious composites (ECC) exposed to dry-wet cycles in sulfate and sulfate-chloride solutions were studied by three-point bending (TPB) beams at the corrosion periods of 0, 30, 90, 130, 180, 270, and 360 days. The digital image correlation (DIC) technique was used to understand the whole fracture process. The fracture toughness and fracture energy were calculated using the proposed method, and the evolution of the horizontal strain field, displacement field, and fracture process zone (FPZ) were investigated. Meanwhile, the compressive and tensile performance of the specimens at the same corrosion periods were analyzed. The results showed that (1) Compared to water immersion, the environments of sulfate and sulfate-chloride were beneficial in improving the compressive and tensile strength, and weakening the tensile ductility. (2) With increasing the corrosion time, the evolution of the unstable fracture toughness can be distinguished into three phases: a stable phase, an increasing phase, and a rapidly decreasing phase, and the initial fracture toughness followed an increasing and then decreasing trend. The fracture energy initially decreased and tended to stabilize after 130 days. (3) By using DIC technology, as the corrosion time increased, the horizontal opening displacement at the notch tip showed a decreasing trend and stabilized after 90 days generally. The fracture path determined through horizontal displacement was well matched with the macrocrack trajectory. (4) The addition of chloride ions helped to improve the mechanical properties of ECC under long-term corrosion, such as compressive strength, unstable fracture toughness, fracture energy, and opening displacement at the notch tip. Compare to concrete, ECC exhibited greater resistance to sulfate corrosion.

Fracture energy of concrete after sustained loading

The fracture energy of concrete after sustained loading is a necessary parameter to calculate the residual carrying capacity of concrete structures in service. This study investigated the fracture energy of concrete after sustained loading by combining experimental observations and theoretical analyses. Firstly, a series of creep fracture tests were conducted on 100 three-point bending beams under various sustained loads, i.e., 75 %, 80 %, 85 %, and 90 % of peak loads. After different loading time, i.e., 10 %, 30 %, 50 %, 70 %, and 90 % of creep fracture lifetimes, the static fracture tests were performed until failure. Then, based on the relationship between the work done by external forces and the energy consumed by the crack propagation of specimens, an analytical model for the fracture energy of concrete after sustained loading was developed, describing the quantitative relationship between the fracture energy of concrete and the crack opening displacement, and the loading time. Finally, the impact of the loading time and sustained load levels on the fracture energy was investigated. The results indicated that the fracture energy of concrete after sustained loading decayed rapidly, with the decay rate gradually decreasing until stability over the loading time. Additionally, specimens subjected to lower sustained load levels experienced a longer loading time for the same crack opening displacement, indicating a greater decay degree of the fracture energy. The analytical model proposed in this study can be employed for predicting and evaluating the crack propagation process and residual carrying capacity of concrete structures during their service life.

Fracture toughness evolution and failure mechanisms of two-dimensional SiCf/SiC composites at temperatures up to 1500 °C in air

Silicon carbide fiber reinforced silicon carbide composites (SiCf/SiC) are of the few most promising materials for high-temperature structural applications. In this study, two-dimensional (2D) plain-woven SiCf/SiC composites were prepared by chemical vapor infiltration process and subjected to single-sided notched beam three-point bending tests from room temperature (RT) to 1500 °C in air. The temperature-dependent bending load–deflection curves and fracture toughness were obtained. The results show that the SiCf/SiC composites exhibit linear deformation characteristics initially, followed by nonlinear deformation behavior which become more pronounced with increasing temperature. The fracture toughness decreases in the range of RT to 1000 °C due to the evolution of components properties, and increases at 1200 °C due to the interface property degradation and fiber pull-out. Above 1200 °C, it decreases with increasing temperature owing to the serious high-temperature oxidation. Further, the failure mechanisms of the 2D plain-woven SiCf/SiC composites at different temperatures was analyzed through macro and micro analysis. The evolution of components properties affected by high temperature and oxidation as well as fiber pull-out play a leading role in fracture toughness of composites. The findings of this study provide important support for the mechanical behavior and failure mechanisms of SiCf/SiC composites at ultra-high temperatures in air.

Study on the Mechanical Properties of a Carbon-Fiber/Glass-Fiber Hybrid Foam Sandwich Structure.

Considering the different structural strength requirements of different parts of fiberglass yachts, carbon fiber/glass fiber hybrid reinforcement can be applied to the skins of sandwich panels in special areas. This paper designs and prepares 12 foam sandwich panel samples composed of pure carbon fiber, a carbon fiber/glass fiber hybrid, pure glass fiber skin, and PVC and SAN foam sandwich, with reference to the layup structure of the outer panel of a fiberglass yacht. Through a comparative analysis of low-speed impact experiments, edge compression experiments, and short beam three-point bending experiments, we seek the optimal carbon fiber/glass fiber hybrid layup design scheme for local structures to guide production. The results show that a reasonable hybrid carbon fiber layup in fiberglass skin can effectively reduce the low-speed impact damage of the sandwich structure, reduce edge compression damage, and improve the bending and compression resistance of sandwich structure. The impact resistance, compression resistance, and shear resistance of the SAN sandwich structure are stronger than the PVC sandwich structure. The carbon fiber/glass fiber hybrid SAN foam sandwich structure can be used for the local structural reinforcement of special parts such as the bow, side, and main deck of fiberglass yachts.

Experimental investigation on damage of concrete beam embedded with sensor using acoustic emission and digital image correlation

With the construction and development of intelligent roads, an increasing number of sensors are being embedded into the road structures. Portland cement concrete (PCC) pavement is one of the main forms of road pavement, but the mechanical behaviors of the PCC pavement with sensor embedding are less studied. In this study, the damage mechanism of PCC pavement is investigated by using the three-point beam bending test, considering the sensor embedding and the coating of the sensor surface. The effect of sensor embedding on the flexural mechanical properties and the damage failure modes of concrete beams are evaluated by using the acoustic emission (AE) technique and the digital image correlation (DIC) technique. Moreover, the concept of degree of coupling (DC) is introduced to reveal the collaborative bearing mechanism between sensor and concrete, and is characterized by an evaluation model considering ultimate bearing capacity, critical instability point, collaborative bearing capacity, AE ring counts, and AE energy. The findings can provide valuable insights in the packaging design of sensor to guarantee the coupling between the sensor and the surrounding concrete for accurately monitoring the long-term performance of road infrastructure.

Study on the fracture mechanical properties of high performance concrete (HPC) with rapid cooling after high temperature

In practical engineering, concrete structures typically undergo high temperatures and fire spray cooling during the process of fire, and high temperatures will cause changes in the microstructure of concrete. Therefore, studying the fracture mechanical properties of concrete after rapid cooling at high temperatures is more in line with the actual engineering situation. This paper sets five temperature conditions (20°C, 200°C, 400°C, 600°C, and 800°C), and after rapid cooling in a water bath, a hydraulic servo machine is used to conduct three-point bending beam fracture tests on plain concrete (PC) and high performance concrete (HPC). The fracture process and mechanism are analyzed using digital image correlation (DIC) and acoustic emission (AE). The research results indicate that the three-point bending unstable fracture load of PC and HPC decreases with the increase of temperature, with the maximum reduction after 800 ℃ high temperature, reaching 87.5% and 82.2%, respectively. After high temperature, the fracture energy of PC and HPC both showed a trend of first increasing and then decreasing. The ductility index of PC and HPC increases with the increase of temperature. The unstable fracture toughness and initial fracture toughness of PC and HPC decrease with the increase of temperature. By combining DIC and AE technologies, the development and fracture mode of cracks in PC and HPC after rapid cooling at high temperature are analyzed. The results showed that the softening effect of concrete is more significant after high temperature, the crack initiation stage is earlier, and the bearing capacity is lower. Furthermore, modern testing techniques are employed to reveal the mechanism of the impact of high temperature and cooling methods on the mechanical properties of HPC from a microscopic perspective. The research results have important reference value for practical engineering.

Experimental study on the effect of polypropylene fiber on compressive strength and fracture properties of high-strength concrete after elevated temperatures

Polypropylene fibers improve the toughness of concrete and reduce the susceptibility of high-strength concrete (HSC) to high temperature spalling. And the mechanical properties of polypropylene fiber reinforced concrete (PFRC) become important after exposure to high temperatures, especially in situations related to engineering uses or repairing concrete structures damaged by fire. This paper presents an experimental study on the compressive strength and fracture properties of PFRC experiencing different temperatures with different fiber contents and lengths. It was shown that the fracture path of concrete becomes longer after experiencing high temperatures. The rate of debonding of mortar and coarse aggregate increases with the temperature rising. The compressive strength of concrete and the peak load and fracture energy of three-point bending beams were both increased by the addition of polypropylene fibers at room temperature, and the compressive strength increased with the increase of fiber content. The addition of polypropylene fibers is able to increase the compressive strength of concrete compared to the control group at experiencing temperatures less than 300 oC. The peak forces of the three-point bending of the concrete beams all show a decreasing trend with the increase in the experienced temperature. The initial slopes of the rising part of the force-loading point displacement and force-crack mouth opening displacement (CMOD) curves all decrease with increasing of temperature, and curves gradually become slower. Addition of polypropylene fibers decreases the peak force of concrete after high temperature. There is no significant pattern in the effect of polypropylene fiber content and length on the peak force and fracture energy of concrete three-point bending beams.

Thermomechanical performance and multiscale modeling of hexagonal boron nitride modified out-of-autoclave manufactured silica fiber reinforced phenolic composites

In this study, high loadings of boron nitride (BN) nanoplatelets were added to silica fiber-reinforced phenolic composites to study the multifunctional impact of BN loading and manufacturing processing on the subsequent mechanical, thermal, and thermomechanical properties. A series of high-quality laminates were made with various loadings of BN using compression-molded out-of-autoclave processing. Three-point bend and short beam shear testing determined the relationship between BN loading and mechanical performance. The fracture properties were analyzed using optical and scanning electron microscopy. The thermal conductivity performance was increased up to a 93% improvement, indicating the thermal management multifunctionality of the modified composites without changing the crosslinking ability or glass transition temperature significantly. The modified performance of hybrid silica/phenolic/BN composites is demonstrated through micromechanical multiscale modeling, where BN loading and particle stress concentrations impact the modulus and strength of the composite.

Rolling shear properties of cross-laminated bamboo (CLB) specimens: A comprehensive study

This study explores the rolling shear properties of cross-laminated bamboo (CLB), an innovative engineering bamboo material. Two typical test methods are used for the experimental work: the modified planar shear tests (MPS) and the three-point short beam bending tests (SBB). The rolling shear strength and modulus are measured in MPS. The shear analogy method is used to calculate the rolling shear strength in SBB. Subsequently, comprehensive numerical models of MPS and SBB are developed, taking into account the material properties of bamboo and adhesives through user material and cohesive zone model. The stress-strain curves and failure propagations of the models align very well with the experimental results. Rolling shear failure was initiated at the interface between the middle layer and outside layer and extended diagonally. Parametric analysis on the cohesive strength of the MPS model shows the variation of loading curves and failure modes. The failure modes of SBB under different span-to-depth ratios are investigated by integrating the shear analogy method and numerical model.

Evaluation of Low- and Intermediate-Temperature Cracking Performance of Fiber-Reinforced Asphalt Mixtures

This study was conducted to assess the impact of aramid fiber reinforcement on the fatigue and thermal cracking performance of asphalt mixtures at intermediate and low temperatures, respectively. The study also involved evaluating the experimental consistency and ranking fiber-reinforced asphalt mixtures (FRAMs) based on their performance. One aggregate (diabase stone), one binder type (PG 76-22), and two combinations of aramid fibers, added at different dosages, were used to produce three FRAMs. These fibers included polyolefin/aramid (PFA) fibers at 0.05% dosage by mix weight and Sasobit-coated aramid (SCA) fibers at 0.01% and 0.02% dosages. An unreinforced (control) mix was also produced without any reinforcement. All mixtures were produced at a batch plant by keeping their binder content constant (at 5.5%). The manufacturer recommended dry and wet mixing times were used for better fiber distribution and represent actual mixing conditions. The laboratory performance of plant-produced FRAMs was assessed to characterize the low- and intermediate-temperature cracking performance. The indirect tension asphalt cracking test, semi-circular bend test, three-point bending beam tests, and uniaxial fatigue tests were performed at intermediate temperature; the disk shape compact tension test and thermal stress restrained specimen test tests were performed at low temperature. Fibers were successful at improving the fatigue cracking of asphalt mixtures based on intermediate-temperature testing results. In addition, fiber reinforcement, regardless of dosage and combination, showed improvements in low-temperature (thermal) cracking performance. Furthermore, based on ranking analysis for selected performance indicators from each experiment, the SCA 0.02% reinforced mix on average showed the highest cracking resistance.