Cracking Performance Research Articles

Presentation of machine learning methods and multi-objective optimization of fracture indices for asphalt rubber mixtures containing wax-based warm mix additives modified by nano calcium carbonate

Warm mix asphalt (WMA) additives have been proposed to overcome the high viscosity problem of crumb rubber modified asphalt (CRMA) binders. Various additives have been used to improve the low-temperature cracking performance of asphalt mixtures, but no study has been conducted to present the optimum additive content in CRMA binders in different loading modes. Therefore, this research aims to present the optimum content of nano calcium carbonate (NCC) to improve the fracture toughness and energy of asphalt rubber mixtures containing WMA additives (slack wax (SW) and polypropylene wax (PPW)). The semi-circular bend (SCB) fracture test was applied under pure mode I, mixed mode I-II, mixed mode II-I and pure mode II loadings at subzero temperature. Machine learning methods, including multivariate regression (MVR) and artificial neural network (ANN) models of group method of data handling (GMDH) and multilayer perceptron (MLP), were used to provide the prediction models of effective stress intensity factor (Keff) and fracture energy (Gf). Finally, the multi-objective optimization of Keff and Gf was performed to obtain optimum NCC content. The results indicated that in MVR model, the outputs had a small correlation with laboratory values, so that R value of MVR was 0.8406 and 0.8011 for Keff and Gf, respectively. Also, it was revealed in MVR that NCC had the highest impact on Keff and Gf significantly. GMDH model results showed that the relationships between predicted and laboratory values of Keff and Gf are appropriately described with R value of 0.9546 and 0.9229 for Keff and Gf models, respectively. In MLP model, different layer structures of the feed-forward neural network were developed to obtain the most accurate structure. It was indicated that MLP with 4–22–1 and 3–19–1 structures had a higher accuracy for Keff and Gf prediction models with R value of 0.9951 and 0.9978, respectively. Finally, by the use of the best model relationships, the results of the multi-objective optimization indicated that 4.91% and 6.37% NCC were the design optimum contents resulting in a maximum of Keff and Gf simultaneously for SW and PPW-modified CRMA mixtures. Moreover, the optimum NCC contents in loading modes of mode mixity Me of 1, 0.8, 0.4 and 0 were 3.62%, 5.12%, 4.08% and 3.42% for SW-modified CRMA mixtures and 4.35%, 6.51%, 7.19% and 2.84% for PPW-modified CRMA mixtures, respectively.

Flexural strength of ultra-high performance concrete beams with stainless steel wire mesh: experimental and finite element analysis

The addition of a stainless steel wire mesh (SSWM) at the bottom of ultra-high performance concrete (UHPC) was proposed for improving the flexural strength of UHPC and solving the problem of low initial cracking performance. A method combining experiments and numerical simulations was used to study the ability of the SSWM to enhance the flexural strength of UHPC and evaluate its cracking resistance. The wire diameter, mesh size, number of steel wire mesh layers, and length of the SSWM were the geometric parameters considered in the experiments. The experimental results showed that the flexural strength of UHPC is improved by SSWM, and the load–deflection curve, ductility, strain distribution, and failure mode of UHPC were assessed. The flexural strength and failure modes of UHPC were evaluated accurately using a numerical model. The wire diameter, mesh size, number of steel wire mesh layers, and wire mesh length parameters were analyzed using the model. The relationship between the flexural strength and the geometric parameters was obtained through an in-depth study of the parameter analysis results using multiple linear regression.

Low-temperature fracture resistance of plant-mixed heat recycled asphalt mixture based on SCB

To investigate the low-temperature crack resistance of plant-mixed heated recycled asphalt mixture, we conducted a semi-circular bending (SCB) test to analyze the effects of the reclaimed asphalt pavement (RAP) content, salt concentration, and loading rate on the crack resistance at −15 °C. The experimental results show that the fracture energy (G f) of the recycled asphalt mixture decreases with an increase in RAP content and salt concentration but increases with an increase in loading rate. When the RAP content is 0%, the Gf of the specimen reaches its maximum value, while when the RAP content is 50%, Gf reaches its minimum value. When the loading rate is 10 mm s−1, the destruction of coarse aggregates in the specimen is much greater than the destruction mode at a loading rate of 2 mm s−1. Meanwhile, as the RAP content increases, the influence of chloride salt on the low-temperature crack resistance of the recycled asphalt mixture fluctuates. According to the quadratic fitting of RAP content and G f, it can be concluded that a lower loading rate is more helpful in analyzing the degradation mechanism of reclaimed asphalt mixture by salt, and a loading rate of 5 mm s−1 ha−1s−1 a significant impact on the degradation trend of the recycled asphalt mixture. Finally, by establishing the relationship between the Mohr-Coulomb expression and the ultimate tensile stress, we obtained the cohesive force (c) and further analyzed the degradation mechanism of the recycled asphalt mixture under the loading rate and chloride salt. However, the effect of RAP content on c is influenced by various factors, which should be considered comprehensively. These research results enrich the mechanism analysis of the low-temperature cracking performance of plant-mixed heated asphalt mixture and provide theoretical guidance for enhancing the low-temperature cracking resistance design of asphalt pavement.

Study of the Effect of Retarder and Expander on the Strength and Cracking Performance of Rubber Concrete Based on Back Propagation Neural Network.

The advantages of rubber concrete (RC) are good ductility, fatigue resistance, and impact resistance, but few studies have been conducted on the effects of different rubber admixtures on the strength of RC and the cracking performance of rubber mortar. In this study, the compressive and flexural tests of rubber concrete and the crack resistance test of rubber mortar were carried out by changing the rubber content and adding expansion agent and retarder in this test. The test results show that the strength of RC decreases with the increase in rubber admixture. At 15% of rubber admixture, the expansion agent and retarder increase the compressive strength and flexural strength of RC the most; the compressive strength increased to 116% (22.6 MPa) and 109% (21.2 MPa), and the flexural strength increased to 111% (4.02 MPa) and 116%. (4.21 MPa). At the same rubber admixture, the expander improves the cracking time of the rubber mortar by about 3 times, and the retarder improves the cracking time of the rubber mortar by about 1.6 times. The BP neural network (BPNN) was established to simulate and predict the compressive and flexural strengths of RC with different admixtures and the cracking time of rubber mortar. The simulation results show that the predicted 7-day compressive strength of RC fits best with the actual value, with a value of 0.994, and the predicted 28-day flexural strength was closest to the measured value, with an average relative error of 1.7%. It was shown that the calculation results of the artificial intelligence prediction model are more accurate. The simulation results and test results show that the expander and retarder significantly improve the strength of RC as well as the cracking performance of rubber mortar.

Influence of performance-graded binders on enhancing asphalt mixture performance with epoxy resin and crumb rubber powder

The evaluation of asphalt mixture fatigue performance holds increasing significance in the context of asphalt concrete pavement and various polymer modifiers. This study focuses on assessing the fatigue and reflection crack performance of two asphalt types: a conventional 10 mm SMA mixture with a fixed PG grade (PG 76–22) and a modified asphalt employing SBS, available in multiple grades (ranging from PG 76–22 to PG 82–22). Additionally, this study incorporates crumb rubber powder (CRP-6%) and epoxy resin (ER-4%) into the conventional SBS-modified SMA binder, reducing conventional asphalt binder consumption and promoting the utilization of recycled waste materials. To achieve this goal, comprehensive evaluations of fatigue cracking performance were conducted on SMA mixtures through multiple stressed creep and recovery tests, Texas overlay tests, and direct tensile cyclic fatigue tests. The results reveal that the modified binder exhibited superior strain recovery and a reduced strain rate in comparison to the reference binder under creep loads at MSCR levels of 0.1 and 3.2 KPa. The findings also indicate a 19.5% load reduction in the modified asphalt mixture with PG 72–22 binders, epoxy, and CRP after 1000 cycles, compared to 39.8% for the conventional mixture with a PG 76–22 binder. Moreover, the modified mixture demonstrated significant improvements, with 3.7 times more repetitions and 3.9 times more interactions to failure at strain levels of 330 and 360, respectively. Importantly, the research highlights the superior fatigue crack resistance performance of the PG 76–28 grade mixture compared to PG 76–22, positioning it as an optimal choice for aged concrete overlay applications. In conclusion, this study contributes to the development of more durable and reliable polymer-modified SMA mixtures enhanced with epoxy and crumb rubber, facilitating the advancement of sustainable road infrastructure.

Complex surface cracks detection and identification by laser array spots thermography with PCA-Frangi processing

In this paper, a method for rapid detection and automatic identification of complex surface cracks based on laser array spots thermography with PCA-Frangi processing is developed. With the Laser Array Spots Thermography (LAST), a complex surface crack in a relatively large surface area can be detected rapidly. In addition, a novel approach utilizing the PCA-Frangi algorithm for feature extraction is proposed to enhance the imaging performance of surface cracks with complex morphology. The results show that the proposed method can extract the cracks and eliminate the interference of array spots to crack identification. Furthermore, this method effectively mitigates the impact of thermal inhomogeneity and thermal noise during the heating process. Finally, the crack features are automatically identified. The simulation and experimental results illustrated that the method enables the accurate recognition of complex surface crack characteristics, further enhancing the overall performance of the crack detection with LAST.

Study on the Performance of Phase-Change Self-Regulating Permeable Asphalt Pavement

Under low-temperature conditions in winter, asphalt pavement is prone to cracking, icing and other distresses, which affect its safety and comfort. Therefore, by incorporating phase-change materials into asphalt and conducting relevant performance studies, the aim is to alleviate low-temperature distress and regulate road surface temperature and expand the application of phase-change materials in asphalt pavement. We mixed the selected phase-change materials with different dosages into the matrix asphalt to prepare phase-change temperature-regulating asphalt and tested the four basic indicators: road performance, latent heat characteristics, temperature-regulating performance, and rheological properties of phase-change asphalt and its mixture. The research results indicate that with the increase in phase-change material content, the penetration, softening point, ductility, and dynamic viscosity of phase-change high-viscosity asphalt gradually increase. Under the constant temperature test conditions of −2.5 °C and −5 °C, the surface icing speed of asphalt binder specimens mixed with phase-change materials is slower than that of specimens without phase-change materials. Adding phase-change materials can improve the high-temperature and low-temperature PG grading of high-viscosity asphalt, effectively improving its high-temperature rutting resistance and low-temperature cracking performance. According to the temperature regulation test results, phase-change temperature-regulating asphalt has a certain regulating effect on temperature under low-temperature conditions, which can slow down the cooling rate of asphalt, reduce the thermal conductivity of permeable asphalt mixture by more than 50%, increase the temperature regulation rate by more than 30%, and improve the ice-melting and snow-melting ability by more than 20%. Phase-change materials have almost no effect on the porosity of permeable asphalt mixtures and can effectively improve the water stability, low-temperature crack resistance, and antiflying performance of permeable asphalt mixtures. Their Marshall stability and rutting stability decrease, but still meet the requirements of the specifications. Applying phase-change materials to permeable asphalt pavement can automatically adjust the temperature of the pavement, reduce the cooling rate of the asphalt pavement during cooling, alleviate the problem of snow and ice accumulation on the asphalt pavement in winter, and thereby improve the performance of permeable asphalt pavement against freeze–thaw cycles.

Effects of asphalt binder type, aggregate type, and gradation characteristics on fracture properties and performance of asphalt mixtures at intermediate temperatures

This study aimed to design and evaluate asphalt mixtures by considering various factors including different binders, aggregate types, and gradation characteristics of the fine portion of mixtures, referred to as the interstitial component (IC). The mixtures were compacted to 93% of maximum theoretical density to prepare specimens for Superpave IDT tests, which included resilient modulus, creep compliance, and fracture tests. Parameters such as failure limit (fracture energy), damage rate (dissipated creep strain energy per cycle), and the relative cracking performance indicator (number of cycles to failure) were assessed for test specimens subjected to the long-term oven aging and the cyclic pore pressure conditioning. The results showed that mixtures with styrene–butadiene–styrene modified binders exhibited slightly higher failure limits but significantly lower damage rates compared to mixtures with unmodified binders, indicating improved cracking performance. Similarly, the limestone mixtures demonstrated equivalent failure limit but much lower damage rate to the granite mixtures, attributed to the porous surface morphology and inherent weakness of limestone aggregates. Notably, even small changes in the IC characteristics of the mixtures yielded substantial differences in fracture properties and performance, a phenomenon believed to be linked to the distribution of asphalt binder and the structure of air voids within the mixture. In conclusion, a thorough examination confirmed the impact of polymer modification and aggregate type on fracture properties and, notably, highlighted the pivotal role of the fine portion's characteristics in determining mixture cracking performance.

Enhanced micro-explosion to improve the yield of light oil in catalytic cracking of water-in-heavy oil emulsion prepared by continuous membrane emulsification

Membrane emulsification provides new ideas for improving the atomization performance of high viscosity heavy oil in catalytic cracking process, thereby improving the distribution of catalytic cracking products. A comprehensive understanding of the micro-explosion characteristics and catalytic cracking of low water content heavy oil emulsion is the key to the application of membrane emulsification technology in heavy oil catalytic cracking process. Therefore, different water droplet sizes and water content of heavy oil emulsion were controllably prepared by continuous membrane emulsification, and their micro-explosion characteristics and catalytic cracking performance were investigated. The evaporation of heavy oil emulsion droplets (water content over 3 vol%) only underwent the heat transfer stage and the fluctuating evaporation stage due to the strong micro-explosion. The micro-explosion delay time of emulsion droplets decreased from 2.631 to 0.434 s/mm2 with increased temperature (300–600 ℃), increased from 0.645 to 1.042 s/mm2 with increased water content (1–5 vol%), and increased from 0.642 to 1.237 s/mm2 with increased average droplet size (1.80–14.6 μm). The child droplets generated after micro-explosion were characterized, and the different heating behaviors were quantitatively distinguished by the average size of the child droplets. Additionally, the micro-explosion performance (i.e. child droplets size and strong micro-explosion probability) of emulsion droplets improved with increasing water content and average water droplet size, while it initially decreased and then increased when the temperature increased. Furthermore, the improvement of micro-explosion performance by membrane emulsification can increase the yield of light oil (up to a maximum increase of 10.82 %) and reduce the yield of coke (up to a maximum decrease of 5.99 %) in the heavy oil emulsion catalytic cracking.

Effect of Basalt Fiber Diameter on the Properties of Asphalt Mastic and Asphalt Mixture.

In this study, basalt fiber having two types of diameters (16 μm and 25 μm) was selected and added to asphalt mastic and asphalt mixtures using different fiber proportions. The influences of fiber diameters and proportions on the properties of asphalt mastic and mixtures were studied. The adhesion behavior of the fiber-asphalt mastic (FAM) interface was evaluated by a monofilament pullout test, and the rheological properties of FAM were evaluated by temperature sweep, linear amplitude sweep, and bending beam rheological tests. In addition, the high-temperature stability, intermediate and low-temperature cracking resistance, and water stability of fiber-modified mixtures were studied by wheel tracking, ideal cracking, a low-temperature bending beam, and a water-immersed Marshall test. The results showed that the interface adhesion behavior between 16 μm fiber and asphalt mastic was more likely in the fiber failure mode at both -12 °C and 25 °C. Adding basalt fiber can significantly improve the high-temperature and fatigue properties of asphalt mastics. Moreover, 16 μm fiber had a better modifying effect on asphalt mastic than 25 μm fiber. The same enhancement trend can be observed in asphalt mixtures. Basalt fibers with 16 μm diameters can improve the high-temperature performance of asphalt mixtures more significantly. In addition, 16 μm fiber could sharply enhance the cracking performance of the mixtures at intermediate and low temperatures, while the enhancing effect of 25 μm fiber on the mixture is insignificant, though both diameters of the fibers have a minor effect on the water stability.

Fabrication and characterization of ZSM-5 zeolite modified with silver and assessing its performance in petroleum waste cracking process

The purpose of this study is to modify the structure of ZSM-5 zeolite with the aim of enhancing its performance in the cracking process for the conversion of petroleum waste into higher-value products. ZSM-5 zeolite was synthesized using a microwave-assisted hydrothermal method subsequently, the structure of the zeolite was modified by incorporating silver using the incipient wetness impregnation method. Then the synthesized sample was evaluated for its performance in a fluid catalytic cracking (FCC) process, conducted under atmospheric pressure and at a temperature of 450 °C. The performance of the silver-doped ZSM-5 zeolite was compared to that of a basic catalyst, which employed USY (ultra-stable Y) zeolite. To characterize the silver-doped ZSM-5 zeolite, various analytical techniques were employed. These included X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectrometer (FTIR), temperature-programmed desorption of NH3 (NH3-TPD) and N2 adsorption–desorption. The findings of the study revealed that the modification of ZSM-5 zeolite's structure with silver led to an increase in the yield of propylene production from 6.99 % to 9.78 %. Additionally, the results demonstrated that the incorporation of silver into the zeolite structure enhanced the yield reaction, as evidenced by the measurement of American Petroleum Institute (API) index. The presence of smaller pores and the specific types of pores in Ag/ZSM-5 zeolite reduced secondary reactions. Moreover, the interaction between silver species and strong acid sites within the modified zeolite structure limited hydrogen transfer reactions and consequently increased the zeolite's overall activity.

Comparative study on the fatigue properties and dislocation evolution of three kinds of aluminum alloys

The detecting and evaluating fatigue performance of aluminum alloys with wide applications have important engineering significance. Three types of aluminum alloys, 1060, 3003 and 6063, were selected to conducted research on tensile and high cycle fatigue properties. It can be found that the relationship between the tensile strength and fatigue strength is not monotonically increasing, the mechanism was also analyzed. The fracture surface and microstructure before and after fatigued were analyzed using scanning electron microscope and transmission electron microscope, the effect of “localized reinforcement” can make the fatigue strength of alloy higher, and the evolution of dislocations under cyclic loading have a significant impact on the tendency of muti-source cracking and fatigue performance. Meanwhile, the positions of knee points and the scatter of the fatigue S-N curves were effect by the strength of materials.

Flexural behavior of long-term loaded RC beams strengthened by ultra-high performance concrete

This study aims to investigate the flexural behavior of reinforced concrete (RC) beams strengthened with ultra-high-performance concrete (UHPC) after being loaded with long-term sustained loads for more than 20 years. Seven RC beams, originally fabricated in 1998, are categorized as the one-time pouring unnotched beam (Overall beam), one-time pouring notched beam (Notched beam), and two-time pouring beam (Repaired beam). These RC beams were firstly tested under the effect of long-term sustained loads which lasted 23.6 years. Subsequently, notched beams were strengthened using UHPC (hereafter named as Strengthened beam), which are tested under four-point bending test to investigate the significance of strengthening using the UHPC. Long-term load effects on the flexural performance of RC beams, including creep, cracking, concrete carbonization, and steel rebar corrosion were tested and analyzed. Test results showed that the maximum carbonization depth was less than the concrete cover depth and the steel rebars corrosion was among 1.51–2.47%, which indicates that the steel rebars inside the beam are well protected and are almost free of rust. The bearing capacity of the strengthened beams were increased by 24.6–48.6% compared with that of the Notched beam, which emphasizes the significance of strengthening using the UHPC. The displacement ductility of the strengthened beams was decreased by 82–94% compared with that of the Overall beam, however no brittle failure was observed during the test. It is worth mentioning that the internal changes, caused by the long-term sustained loading, could not be completely changed by adopting UHPC strengthening, while the stiffness reduction caused by long-term loading considerably influenced the flexural behavior of the UHPC strengthened beams. In addition, more attention shall be paid to the UHPC-NC vertical interface which remarkably affected the flexural performance of the Strengthened beams.

An Approach to Incorporate Amplitudes and Wavelengths of Transverse Crack for Predicting IRI

A methodology was proposed that can improve pavement smoothness prediction. As an initial attempt, smoothness due to solely transverse cracking was investigated. The new model incorporated amplitudes and wavelengths of transverse crack which are directly related to IRI computation. The crack amplitude and wavelength were measured by automated profiler from the MnRoad test roads and formulized with mathematical form expressed with respect to various crack depths and widths, respectively. Instead of conventional severity criteria, crack severities could be determined by crack depth and width in the mathematical form. Utilizing digital signal processing techniques, cracked surfaces with various severities were successfully prepared. The computed IRI values were found to be significantly related to crack severities expressed by width and depth. Then, an IRI prediction model was derived containing the simulated various crack severities and crack occurrences. Ultimately, the IRI model was validated using transverse crack performance data from MnRoad. The model incorporated spectral information that could fundamentally and accurately predict IRI increment by crack. This confirmed the necessity of incorporation of amplitude and wavelength information in predicting IRI.

Structural Health Monitoring of Fiber-Reinforced Concrete Prisms with Polyolefin Macro-Fibers Using a Piezoelectric Materials Network under Various Load-Induced Stress

This experimental study investigates the influence of synthetic macro-fibers added in fiber-reinforced concrete (FRC) prismatic specimens on their flexural response and overall cracking performance. Application of a novel structural health monitoring (SHM) system that implements the electromechanical impedance (EMI) technique and the use of piezoelectric lead zirconate titanate (PZT) transducers installed in the FRC prisms are also included. The applied PZT-enabled EMI-based monitoring system was developed to diagnose damage and the overall performance in reinforced concrete (RC) structural members subjected to cyclic repeated loading, simulating seismic excitations in existing RC buildings. The paper also aims to determine the sensitivity of the real-time, wireless, and portable monitoring technique corresponding to the location, the distance, the direction of polarization of the PZT transducers and the location and magnitude of damage due to flexural cracking. Further, the influence of the effect of stresses corresponding at various loading levels and the observed changes in the ΕΜΙ frequency response of the PZT transducers are also examined. Test results indicated that cracking detection is achieved using this SHM system by prompt damage level assessment due to the FRC’s flexural load at early seismic loading stages in existing RC buildings.

Laboratory evaluation of the effect of microfibers on the low-temperature cracking performance of grouted macadam mixtures

Grouted Macadam (GM) mixtures are a composite of bituminous and cementitious phases used as pavement semi-flexible overlays because of their high static bearing capacity and rutting resistance, good durability, and proper resistance to chemical attacks and fossil fuels. However, these mixtures do not have good performance at low temperatures. Reinforcement by fibers is a popular method to improve the performance of asphalt and concrete mixtures and has the potential to be used to reinforce GM mixtures. This study aims to reinforce both bituminous and cementitious phases of GM mixtures using glass based (Microcorta) and polypropylene based (PP) fibers, respectively. The bituminous phase of the first group of the GM mixtures was reinforced with 0.2, 0.4, and 0.6 vol% of glass microfibers (MC). In addition, 0.2, 0.3, and 0.4 vol% of PP fibers were used to produce the cement grout of the second group of GM mixtures. In the next step, the performance of each group was compared with that of the fiber-free samples using a three-point bending test (TPB) and low-temperature indirect tensile test (IDT). Based on the obtained results, GM mixtures’ best low-temperature performance in both IDT and TPB tests was obtained for mixtures containing the highest percentage of fibers (0.6% of MC and 0.4% of P.P fibers). Also, it was observed that the reinforcement of the bituminous phase increased the fracture strain tolerance (FST) in the TPB and IDT tests by 66.19% and 25.01%, respectively, compared to fiber-free samples. Moreover, using fiber-reinforced cement grout has been able to enhance the FST index in the TPB and IDT tests by 91.87% and 30.9%, respectively, compared to fiber-free samples. Overall, the results demonstrate that the reinforcement of both bituminous and cementitious phases of GM mixtures by microfibers can help improve their ability to resist low-temperature cracks.

In vitro corrosion-assisted cracking of AZ31B Mg alloy with a hybrid PEO+MWCNTs/PCL coating

The effects of multi-walled carbon nanotubes (MWCNTs) incorporation and polycaprolactone (PCL) post-treatment on the environmental-assisted cracking behaviour of a plasma electrolytic oxidation (PEO) coated AZ31B Mg alloy were elucidated in this study. Slow strain rate tensile (SSRT) experiments were carried out in simulated body fluid (SBF) for the bare material and different coating systems with and without MWCNTs and PCL overlay. Electrochemical impedance spectroscopy (EIS) and microscopic examinations (SEM and optical) were also conducted to reveal the role of corrosion on the mechanical response. In spite of the significant positive influence of the PEO coatings (with and without MWCNTs) on the bio-electrochemical behaviour of the AZ31B alloy, the environmental-assisted cracking performance was only marginally improved. Furthermore, PEO+MWCNTs/PCL coating system increased the fracture strain of the specimens by 7% compared to the uncoated specimens. Based on the SEM and optical micrographs, hydrogen embrittlement was suggested as the main cause of failure of the coated specimens under the in vitro slow strain rate test conditions.

Improving Corrosion and Stress Corrosion Cracking Performance of Machined Biodegradable Alloy ZX20 by HF-Treatment

The treatment with hydrofluoric acid (HF-treatment) was suggested to be an effective way of improving the corrosion resistance of Mg alloys, including Mg-Zn-Ca (ZX) ones used for biodegradable implants. However, the effect of the HF-treatment on the stress corrosion cracking (SCC) susceptibility of ZX alloys has not been reported yet, although this phenomenon can induce premature brittle failures of the metallic medical devices, and thus, it is critical for their in-service structural integrity. In the present study, the effect of the HF-treatment on the microstructure, cytotoxicity, corrosion rate, mechanical properties, and fracture and side surface characteristics of the as-cast ZX20 alloy were investigated with the use of scanning electron microscopy, immersion, and slow-strain rate tensile testing in Hanks’ solution and indirect cell viability tests. It is found that the HF-treatment exerts no cytotoxic effect and results in a significant reduction in corrosion rate (up to 6 times of magnitude) and SCC susceptibility indexes (up to 1.5 times of magnitude). The observed improvement of corrosion and SCC performance of the alloy by the HF-treatment is found to be attributed to three effects, including (i) formation of the protective surface film of MgF2, (ii) removal of surficial contaminations originating from sample preparation procedures, and (iii) dissolution of surficial secondary phase particles. The mechanism of corrosion and SCC in the specimens before and after the HF-treatment are discussed.

An Evaluation of the Cracking Resistance of Steel- and Glass-Fiber-Reinforced Asphalt Mixtures Produced at Different Temperatures

This study focuses on the effects of the production temperatures, warm mix asphalt (WMA) additive, and fiber content on the cracking resistance of steel- and glass-fiber-reinforced asphalt mixtures. By using three different approaches, which included different mixing and compaction temperatures, along with the incorporation of a WMA additive, the samples were produced utilizing the Marshall mix design method. The low-temperature cracking resistance and bottom-up fatigue cracking resistance of the asphalt mixture samples were assessed through indirect tensile (IDT) tests performed at two different test temperatures: −10 °C and 20 °C, respectively. According to the fracture work density values, glass fibers significantly improve the low-temperature cracking performance of asphalt mixtures. Furthermore, it was found that the low-temperature cracking resistance of the hot mix asphalt (HMA) mixtures containing fibers was similar to that of the mixtures prepared using the WMA additive at 15 °C lower mixing and compaction temperatures than the HMA mixtures. To conclude, the WMA additive improved the compactability of the steel- and glass-fiber-reinforced asphalt mixtures without compromising the low temperature cracking performance, despite the low mixing and compaction temperatures.

Anti-reflective crack performance of high viscosity and high elasticity asphalt mixture for ultra-thin wear layer

Anti-reflective crack performance of high viscosity and high elasticity asphalt mixture for ultra-thin wear layer