5,696 research outputs found
Clay mineralogy and pedogenesis of Ultisols and Inceptisols with placic horizon in the subalpine forest of Taiwan
No full text20 Universala Kongreßo de Esperanto S.P. Q.A. Antverpeno Datum
No full text20 UNIVERSALA KONGRESSO DE ESPERANTO S.P. Q.A. ANTVERPENO DATUM
20 Universala Kongreßo de Esperanto S.P. Q.A. Antverpeno Datum ( -
Soil characteristics and genesis of inceptisols with placic horizon in subalpine forests of Taiwan. In: Soil Classification 2004
No full textCharacterization of Failure and Permanent Deformation Behaviour of Asphalt Concrete
No full textAsphalt concrete is a viscoelastic material consisting of aggregates, filler and bitumen. The response of asphalt concrete is highly dependent on temperature, loading rate and confining pressure. Permanent deformation is one of the most important distresses developing during the flexible pavement service life. The total deformation which is visible at the pavement surface is the sum of the deformation that developed in each and every layer. In this thesis however attention will only be paid to permanent deformation of the asphalt layers. The main goal of this research was to investigate and better understand the permanent deformation behaviour of asphalt mixtures at 50°C which is a temperature that regularly occurs in asphalt wearing courses in the Netherlands and which therefore is applied in the Dutch standard for testing the resistance to permanent deformation of wearing courses. The thesis is divided in two parts. The first part focuses on sample preparation, testing procedures and fundamental properties of dense asphalt concrete (DAC) and porous asphalt concrete (PAC) mixtures and skeletons. In the second part the focus is on the prediction of permanent deformation. In the first part of this research special attention was paid to the following aspects: Effects of end constraints on test results Friction between the ends of the specimen and the top and bottom loading platens introduces extra confinement at the top and bottom of the specimen. In this research an extensive monotonic compressive testing program was performed on DAC and PAC mixtures under two different end contact conditions being full friction and reduced friction. “Full friction” was achieved by gluing the specimen to the top and bottom loading platens. “Reduced friction” was obtained by using a sandwich-shaped friction reduction system which consisted of two thin rubber sheets and vacuum grease in between. The results show that in the case of “full friction” the failure stress is overestimated and the displacement at failure is underestimated. The results also show that in the case of uniaxial testing without confinement and when using the friction reduction system, a deformation correction is needed to obtain the true deformation of the specimen. When confining pressure is applied deformations due to the friction reduction system can be ignored. The stress-strain behaviour of asphalt mixtures The permanent deformation behaviour of asphalt mixtures is highly dependent on temperature, stress conditions and number of load repetitions. A better understanding of the stress-strain behaviour of asphalt mixtures is beneficial for a better understanding of the permanent deformation. Therefore an extensive monotonic compressive test program was conducted on DAC and PAC at 40°C and 50°C with 3 various confining pressures and 5 different loading rates. The test results showed that the stress-strain behaviour of DAC significantly depends on temperature, strain rate and confinement. The results also showed that at high temperatures the PAC mixture behaves much alike a granular material with little cohesion. In this case the skeleton of PAC plays a significant role in the mechanical behaviour and this behaviour is highly dependent on the level of confinement. Behaviour of aggregate skeletons Permanent deformation develops at elevated temperatures. At elevated temperatures, the contribution of the aggregate skeleton becomes crucial. For this reason monotonic compressive tests were conducted on DAC and PAC skeletons at two strain rates and two confining pressure levels. The stress-strain behaviour of the DAC and PAC skeleton were compared with the stress-strain behaviour of both mixtures. The results implied that the bituminous mastic in DAC acts as a binder and contributes to the behaviour of the DAC asphalt mixture. The results also showed that the PAC aggregate skeleton shows typical elastoplastic behaviour regardless of the strain rates. In the second part of this thesis repeated load triaxial tests to study the development of permanent deformation were performed on the DAC mixture at 50°C and the following questions related to permanent deformation of the DAC mixture were discussed. Scatter observed in permanent deformation results A power function was used to model the obtained permanent deformation. A large scatter in the model parameters was observed even at the same stress ratio for selected test specimens. The possible relation between the scatter on one hand and the air voids content and resilient modulus of specimens on the other was studied. CT scanning was used to investigate the internal structure of the intact and tested specimens. The results showed that there is no clear relationship between air voids and the parameters describing the development of the permanent deformation with increasing number of load repetitions. The results also showed that the model parameters were stress dependent and a strong relationship was found between the model parameters and the resilient modulus after 1000 load repetitions. The CT scan results showed that different failure modes took place in the permanent deformation tests and that the internal structure of specimens is important for the development of permanent deformation. It is believed that part of the scatter in the test results can be explained by the variation in internal structure. Influence of loading pattern on permanent deformation The influence of different loading pulses and rest times on the permanent deformation of DAC was also investigated by performing Triaxial Repeated Load Permanent Deformation (TRLPD) test. The tests were performed at two different loading patterns, being 0.2 s load + 1.8 s rest and 0.4 s load + 0.6 s rest, and at two confinement levels of 150 kPa with a stress ratio 0.43 and 100 kPa with a stress ratio 0.3. The results showed that the stress ratio has a significant influence on the permanent deformation while the loading time has little influence on the development of permanent deformation. At the same stress level it seems that the longer loading time does not result in larger permanent deformation. Evolution of the resilient modulus in relation to the number of load repetitions In order to obtain a better understanding of the relationship between permanent strain and resilient strain which is developed in the DAC test specimens during the repeated load triaxial tests, the evolution of the resilient modulus of DAC with the number of load repetitions was investigated and modelled. The results showed that the resilient modulus of DAC reduced during the first load repetitions and tended to take a constant value after 1000 load repetitions. Evolution of Burgers’ model parameters in relation to the number of load repetitions The measured total strain was decomposed into elastic strain, delayed elastic strain and viscous permanent strain and modelled by means of the Burgers’ model. The evolution of Burgers’ model parameters obtained at two different loading patterns was investigated in this study. It was found that the value of the parameter representing the dashpot in series, used for modelling the permanent deformation, increased with increasing number of load repetitions and tended to be constant after thousands of load repetitions. This value however strongly decreased when dilation of the specimen occurred. The loading pattern had a significant influence on the value of this viscous parameter Shake down limit in permanent deformation of DAC In order to explore the existence of a shakedown limit for the tested DAC mixture, five representative permanent deformation tests were analyzed. From this analysis it appeared that below a stress ratio of 0.3 (the ratio of applied vertical stress to vertical stress at failure at the same confinement level) only a limited amount of permanent deformation developed after a large number of load repetitions. The stress ratio of 0.3 is proposed to be the shake down limit at 50°C for the test conditions and DAC mixture used in this research. Permanent deformation modeling based on Dissipated Energy Concept Most of the permanent deformation prediction models are simply relating permanent deformation to stress conditions and the number of load repetitions. In this study a permanent deformation model was developed based on dissipated energy. It was shown that the initial dissipate energy, the applied stress level and the number of load repetitions explain very well the permanent deformation development.Structure EngineeringCivil Engineering and Geoscience
Extending the Lifespan of Porous Asphalt Concrete
No full textPorous Asphalt (PA) concrete is widely used as a surfacing layer on highways in the Netherlands. The service life of PA wearing courses is limited because of the fact that it is vulnerable to raveling. The possibilities of applying preventive maintenance to PA wearing courses by means of spraying rejuvenation products on the pavement surfaces are being investigated with high interest in the Netherlands. A material which has the ability to penetrate into the bituminous binder and soften (rejuvenate) the hardened bituminous binder in the mortar is defined as a rejuvenator. Spraying rejuvenators on asphalt pavement surfaces before raveling starts (during the initiation of damage) might influence the characteristics of the hardened bituminous binder such that the service life of the PA surface layer is extended. Considering the fact that the rejuvenation effectiveness of potential rejuvenation products is not clear, they are called Surface Treatment Products (STP) in this research. The main objectives of this research are the investigation of the effect of surface treatments on the microstructure and performance of PA wearing courses and the assessment of their rejuvenation effectiveness. Three surface treatment products were applied on two field trials of 5 year old PA pavement surfaces, respectively on the A50 and A73 highways. Computed Tomography (CT) scanning with a conventional medical CT scanner was performed on the PA concrete cores that were obtained from the field trial sections to measure volumetric properties like air voids and mortar contents. It was found that the difference between the mean values of the air voids contents for the PA concrete cores from the reference (untreated) and treated sections is not statistically significant in most of the cases. CT scanning with a high-resolution industrial CT scanner was used to detect the surface treatment products. Two parameters, the mortar film thickness and the surface treatment product content, were used to quantify changes in the microstructure due to the surface treatments. The treated PA concrete samples showed an increased mortar film thickness, which indicates the presence of bituminous binder added by the surface treatment products. Visual inspections on PA concrete thin slices with an optical microscope were performed to investigate the microstructure of the treated PA concrete samples. Micro cracks were observed in the reference PA concrete samples but no micro crack was found in the treated PA concrete samples. To determine the rejuvenation effectiveness of surface treatment products, artificially aged PA 0/16 concrete and mortar specimens were produced in the laboratory and the surface treatment products were applied to the specimens. The indirect tensile stiffness modulus and indirect tensile strength were measured on the PA concrete specimens. The results did not show a difference between untreated and treated specimens. For the mortar a special 3D finite element was developed before dynamic shear testing to study the influence of rejuvenation (diffusion inside the mortar) on mortar columns by simulating dynamic shear tests. From the results clear effects on the rheological behavior was shown. Based on the finite element results dynamic shear tests were used to measure the rheological and shear fatigue properties of mortar specimens. The results for the treated mortar specimens did not show a change in complex shear modulus and phase angle or shear fatigue properties compared to the reference mortar. It was concluded that no rejuvenation of the test samples did occur. Another finite element model was created for analyzing the stresses and strains as a result of traffic loads in a reference and treated PA pavement surface. The results showed that because of the added binder, the surface treatment does reduce the stresses, strains and dissipated energies in the mortar bridges at and close to the surface of the pavement, which will result in a higher fatigue life. In addition, the Rotating Surface Abrasion Test (RSAT), three-point being tests and nano-indentation tests were performed on the PA concrete cores taken from the reference and treated sections. The RSAT results for the treated PA concrete cores seem to indicate a lower stone loss than the reference PA concrete cores. The treated PA concrete beams showed higher mean stiffness values than the reference beams. From the nano-indentation tests, the presence of bituminous binders added by the surface treatment products to the mortar of the PA concrete was proven. Based on all the results, it was concluded that no rejuvenation took place. The product will have an effect. But that is because of added binder by the product. Furthermore, it was recommended that preventive maintenance interventions should be based on optical microscopy and nano-indentation tests on thin slices from small cores (?40 mm) rather than visual surveys of the pavement surface.Structural EngineeringCivil Engineering and Geoscience
Asphalt Mixture Fatigue Testing: Influence of Test Type and Specimen Size
No full textFatigue characterization of an asphalt mixture is commonly estimated by laboratory fatigue tests. Based on the classical fatigue analysis, fatigue lives obtained from different test devices are not comparable even when they are performed at the same test conditions. It is believed that there are two main reasons causing the difference in fatigue results being the difference in stress-strain distribution of the different specimens and the fatigue analysis approach. This research focuses on the harmonization of the fatigue results obtained from the different methods, which are recommended by the European standard EN 12697-24. The main goal is to find a correlation between the different fatigue test methods and to improve the classical fatigue analysis approach to better represent the actual fatigue characteristics of asphalt mixtures. To realize the main objective of the study, an extensive fatigue testing program was carried out on dense asphalt concrete 0/8 (DAC 0/8). In the program, uniaxial tension and compression (UT/C) fatigue tests, four-point bending (4PB) fatigue tests and indirect tensile (IT) fatigue tests were performed. For each fatigue test, specimens with different sizes were tested to explore the size effect on the fatigue results. In order to limit the test program, the tests were performed in two loading modes, at two temperatures and one frequency. For the 4PB fatigue test, the measured displacement highly depends on the properties of the loading frame. Calibration tests on the 4PB test setup were conducted to obtain the pure bending deflection of the beam. Comparison of the fatigue results obtained with the different test methods at the same test condition and loading mode shows that the fatigue life from the 4PB test is the longest and from the IT test is the shortest. Because of the homogeneous tensile strain field, the UT/C and IT fatigue results are not significantly influenced by the specimen size. However, the 4PB test results depend on the dimension of the used specimen, because the stress-strain field of the beam specimen varies along the length and cross section. The partial healing (PH) model was used to determine the relationship between the UT/C and 4PB fatigue results in strain-controlled mode. It is a material model that describes the evolutions of the stiffness and phase angle for a unit volume during testing. This implies that the model can be directly applied to the fatigue results obtained from the “homogenous” tests, the UT/C test, because the strain is uniformly distributed throughout the specimen. When analyzing the 4PB results, the backcalculated stiffness is not the local stiffness of the material but the so-called weighted overall stiffness of the whole specimen. Therefore a weighing procedure is required to calculate the weighted overall stiffness modulus from the local stiffness by taking into account the dimensions and the strain distribution of the specimen. By adjusting the model parameters, the PH model provides a good simulation for the evolutions of the stiffness and phase angle. All the model parameters can be expressed as functions of the applied strain level. The trends of the parameter ??1 and ??2 indicate the existence of an endurance limit. The predicted endurance limit obtained by the UT/C test is around 68 ?m/m for the tested DAC 0/8 mixture, which does not change with specimen size and temperature. For the 4PB fatigue test, the local stiffness at different parts of the beam can be calculated by means of the PH model. The evolution of the calculated stiffness at the surface in the midsection of the beam is comparable with the UT/C fatigue results when the pure bending strain on the beam surface is equal to the tensile strain in the cylinder. Therefore the PH model offers a possibility to compare different fatigue results. In the second part of this research, the yield surface concept was applied to develop a new fatigue analysis approach. As a visco-elastic material, the yield surface of an asphalt mixture highly depends on temperature and strain rate. Therefore, monotonic uniaxial compression (MUC) and monotonic uniaxial tension (MUT) tests were performed at different temperatures and strain rates to derive such yield surfaces. For the three fatigue tests, the yield surface at the critical location of the specimen was determined in the I1-?J2 space. The fatigue results were then interpreted by comparing the actual stress condition with the yield surface. A new parameter R? was introduced as an indicator of the “safety against failure”. By comparing the R? values at the different locations of the specimen for the IT test, the weakest points are found at the locations with the maximum horizontal tensile strain, which are close to the loading strips, instead of the center of the specimen. A straight line was found by plotting R? at the critical location and the fatigue life on a log-log scale. Compared to the traditional fatigue analysis, the size effect on the fatigue results was excluded by using this new fatigue relation. For the stress-controlled mode, the fatigue lines obtained from the UT/C test show a good agreement with the IT fatigue results. Of course the influence of temperature and loading mode still exists in this new fatigue method. In the normal coordinate, when the fatigue life tends to infinity, R? becomes a constant value, denoted by Rlimit. The parameter Rlimit represents the endurance limit in a three-dimensional state. This value does not change with specimen size and test type but is influenced by the temperature and loading mode. Based on all the test results and their analysis in this research, it was concluded that the UT/C fatigue results are material properties and not influenced by specimen size. The PH model provides a good simulation of fatigue behavior of the asphalt mixture and is able to find the correlation between the UT/C and 4PB test results. The developed fatigue analysis approach characterizes the fatigue performance of asphalt mixtures in three-dimensional state, which is more close to the field situation. The endurance limit predicted by the new fatigue approach is independent of the specimen size and fatigue test type.Structural EngineeringCivil Engineering and Geoscience
Characterization and Identification of Bituminous Materials Modified with Montmorillonite Nanoclay
No full textMontmorillonite (Mt) nanoclay is a layered silicate mineral with a 2:1-type layer structure, two tetrahedrals sandwiching one octahedral. In recent decades, it is successfully introduced into polymer systems to form polymer-clay nanocomposites (PCN) in which the silicate layers of the Mt are randomly and homogeneously dispersed at a molecular level in the polymer matrix. Due to the addition of Mt, some properties of PCN, such as the mechanical, thermal and gas barrier properties, were superior to those of pristine polymers. Based on this idea, natural and organo Mts were used to modify bitumens with different penetration grades in this study. Some rheological, ageing and fatigue properties of the modified bitumens and mortars were characterized. High-shearing mixing method was used to prepare the modified bitumen; X-ray diffraction and micro-CT scanning were employed to observe structures of Mts in bitumen; DSR equipment was adopted to characterize the rheological properties; the rolling thin film oven (RTFO) and pressure ageing vessel (PAV) methods were used to simulate the short term and long term ageing on base and Mt modified bitumens, respectively. Fatigue tests were performed on bitumen and mortar samples which consisted of bitumen, filler and sand at a weight ratio of 0.34:0.30:0.36, as well as on a dense graded asphalt mixture. XRD results indicated an intercalated structure of organo Mts in the bituminous matrix. A phase separated structure of natural Mt was found in the base bitumen. Micro-CT images further proved that natural Mt acted like a conventional filler at micrometer level. The interaction between the Mts layers and bitumen changed its viscosity and dynamic response as characterized by means of the DSR. Reinforced shear thinning was observed on the modified bitumens at a liquid state, which implies a better drainage resistance of asphalt mixture during transportation. The results indicated that organo Mts improve the short term ageing resistance of base bitumen. The main reason for this improvement is that the barrier properties of Mt particles hinder the penetration of oxygen. Meanwhile, the reduction of volatilization of the oil components of bitumen due to these barrier properties can be another reason. However, a less effective improvement was observed for the long term ageing using the PAV. That is because organo Mt platelets automatically accumulated to reduce their surface area under tough testing conditions in the PAV. This accumulation weakened the barrier properties of the Mts. It is believed however that organo Mts will improve the long term ageing behaviour of bitumen in the field because the state of the Mt will be very stable and no accumulation as occurred in the PAV will happen. The addition of organo Mts can change the fatigue properties of bitumen and even mortar. This change was influenced by the type of the surfactant on the Mt which determined the interfacial interaction between the bitumen and the Mt. Because of the heterogeneous character of asphalt mixtures and their complicated failure mechanism, the fatigue test on the asphalt mixture with the modified bitumen only gave a limited improvement of this property. Finally, some important aspects are given for further research. Based on the present research results, the organo Mt can be an alternative to modifiers used in the bitumen to sustain the durability of asphalt pavements.Design and ConstructionCivil Engineering and Geoscience
Self Healing of Asphalt Mixtures: Towards a Better Understanding of the Mechanism
No full textTraffic is increasing rapidly in terms of number of vehicles and also in axle loads. In order to maximize the availability of the pavement and to minimize hindrances to traffic because of maintenance works, long life pavements are needed. An asphalt pavement with self repairing capabilities is believed to be very useful to this respect. The self healing phenomenon of asphalt mixtures is known for many years by road engineers. Bituminous materials are expected to repair themselves during hot summers and (long) rest periods. However, the underlying mechanism is not well understood, and a proper way to measure it is not available. Research questions are: what is the self healing phenomenon, how to measure it effectively and efficiently and how to upgrade it if possible. In order to answer these questions, investigations were carried out in this thesis. This research focuses on understanding the self healing mechanism of bituminous materials and the effects of material modifications, by means of testing and modelling. The research started with a critical literature review. Preliminary research was conducted to explore possible self healing modifiers. Novel self healing modifiers like ionomers, supermolecular rubbers and nanoparticles were chosen and investigated. Upon analyzing the change of the material properties and the self healing capability due to modifications, it was observed however, that all the novel modifications used in this research are not quite beneficial for the self healing improvement of bituminous materials. A normal soft bitumen was observed to be the best healer among all the modified bitumens tested. Further research was conducted to assess the self healing capability of bituminous materials in further detail. Three test methods were developed to mimic the self healing phenomenon at different levels being from bitumen level to mixture level. The self healing phenomenon was directly related to a measurable crack. In each of the test methods used, cracks were produced first in a controlled way, and after that the healing process of these cracks was investigated. The test methods covered the following aspects: \u95 A two-piece healing (TPH) test was developed to investigate the self healing behaviour of pure bitumen using the Dynamic Shear Rheometer (DSR). During the TPH test, the healing process was mimicked by pressing two pieces of bitumen together in a parallel-plate system. The development of the complex shear modulus during the closure of the gap width and during healing rest periods was monitored and used as a healing indicator. \u95 A modified direct tension test was developed to assess the self healing capability of bituminous mastics. The cracks were first introduced via mechanical loading, and then healing rest periods were applied. After healing, the specimens were reloaded to determine the recovery of the material strength; this recovery was used as a healing indicator. This test can be used to investigate the self healing capability of an open crack with two total fractured surfaces and to determine the self healing capability of meso cracks. \u95 A beam on elastic foundation test (BOEF) was developed to investigate the self healing phenomenon of asphalt mixtures with a notched asphalt concrete beam fully glued on a low modulus rubber foundation. After a crack is produced by imposing monotonic loading, the BOEF setup allows fully closure of the crack due to the confinement of the rubber foundation. After a healing period, the beams were reloaded and the stiffness recovery and strength recovery were used as indicators of healing. \u95 The results of the various tests showed that the self healing capability of bituminous materials can be ranked successfully at different healing times, temperatures and damage levels. The self healing process of damage in bituminous materials consists of two main phases, namely the crack closure and the strength gain phase. The driving force can be either thermal (temperature) or mechanical (by confinement, pressure). The self healing capability is related to the viscosity of the bitumen, which increases with increasing healing time, temperature and when the crack size is very small. Finite element modelling was done to further investigate the self healing phenomenon in the tests. A smeared type cohesive zone model was used to model healing by defining the stiffness and strength recovery process. In this way, the self healing phenomenon was directly linked to a crack repairing process. Based on the research results, a better understanding of the self healing phenomenon was achieved. This thesis ends by discussing some important aspects of building a durable asphalt pavement with self healing capabilities. The self healing capability of an asphalt mixture should be optimized to obtain pavements with an enhanced durability.Structural EngineeringCivil Engineering and Geoscience
Towards a Performance Evaluation Method for Durable and Sustainable Thin Surfacings
No full textThin surfacings are widely used as surface layers to provide additional functions and to extend the service life of existing pavements. They can protect the treated road surfaces from external aggressive substances, the degeneration process of weather and the ageing caused by Ultraviolet light and oxygen. Antiskid surfacing is one type of thin surfacings. It refers to road surface treatment which includes high-friction aggregates and an adhesive binder to bond the aggregates to the road surface. Antiskid surfacing is designed to provide skid resistance, which means excellent adhesion property is then necessary for binding the aggregates together on the surface. So binders with high adhesion strength with aggregates are strongly required. In the Netherlands, most of the airfield runways used tar-containing binders for the antiskid surfacings. Unlike bitumen based materials, tar-containing surface layers, because of the unique chemical and molecular structure of refined tar, are inherently resistant to chemicals and can provide better adhesive property. However, tar-containing binder is toxic and carcinogenic because of its high Polycyclic Aromatic Hydrocarbons (PAHs) content. It cannot meet the Dutch environmental standards and hence will not be allowed for antiskid surfacing on the runways. Therefore, alternatives to tar-containing binders are urgently required. Research on this topic has been being under investigation for a number of years. This research mainly focuses on the definition of requirements for the alternatives, together with a design approach on thin surfacings. Firstly, specimens with tar-containing antiskid layers on the surface were collected from six airfields’ runways. Fourier Transform Infrared, surface characteristics, tensile adhesion and shear adhesion at the interface were investigated. The tar-containing antiskid layers have a minimum 1.26 mm of texture depth and can keep this texture depth for a long service life. The improved pull test and shear test methods are suitable for evaluating the adhesive properties between thin antiskid surface layer and underlying asphalt mixture layer. The shear strength at the interface between tar-containing antiskid layer and underlying asphalt mixture layer is higher than the value at the interface between asphalt mixture layers. The conclusions from these test results are used as benchmarks for alternative antiskid surfacings. Secondly, newly designed binders, which are considered as potential binders for antiskid surfacings, were researched. Copolymer modified bitumen emulsion (MBE), 2-component Modified Epoxy Resin (MER) and 2-component Epoxy Modified Bitumen (EMB) were included. The curing behavior, direct tensile strength, high temperature resistance, weather resistance and low temperature relaxation properties were studied by means of Direct Tensile Test, oven ageing and weatherometer ageing, Dynamic Shear Rheometer test, Dynamic Mechanic Thermal Analysis and Relaxation test. Test results indicate that the investigated 2-component epoxy modified bitumen can be designed as a suitable binder for antiskid surfacing, with good high temperature resistance, qualified relaxation behavior, sufficient tensile strength and enough failure strain. Thirdly, one of the researched 2-component epoxy modified bitumen was then used to design antiskid surfacing in the lab. The surface characteristics, resistance to tensile stress and shear stress were then investigated. Noise-reducing thin surface layers were also included in this research. The results show that EMB based antiskid layer can provide better adhesion at the interface than tar-containing antiskid layer and polymer modified bitumen based antiskid layers. Fourthly, the Finite Element Models of antiskid surfacing were developed to simulate the loading condition in the antiskid surface layers. The viscoelastic properties of EMB and MBE were used as input. The calculation shows that the antiskid structure has huge influence on the resulting binder behaviors. The stresses generated in the EMB binder are slightly higher than in the MBE binder, while the MBE is subjected to much higher maximum principal strain and shear strain levels. Furthermore, the EMB binder has better ability to recover after loading. The aggregate skeleton has a higher influence on the stresses and strains in the soft MBE binder than on the stresses and strains in the EMB binder. At the end, some recommendations are given for further research. Trial sections in the field and fuel resistance are suggested. Fatigue property and failure mechanics are also recommended to investigate the damage mechanisms with FEM model.Structural EngineeringCivil Engineering and Geoscience
Comparison of Three Strategies for Buzz-Saw Noise Propagation in an Aeroengine Intake with Flow Distortion using CFD
No full textThe expense of computational methods that can accurately predict the tonal acoustic field in an aeroengine intake is a current limitation for understanding current and future challenges in aeroengine noise, such as the impact of increased flow distortion with UHBR (Ultra-High Bypass Ratio) turbofan designs. In this study, the intake propagation of shock-associated fan tone noise through a distorted inflow is considered. Three numerical methodologies are applied to explore novel methods for reducing the computational demand of representative and accurate calculations. The datum case considers the full intake domain with a fully structured computational mesh. A part-span approximation neglects low-span regions of the duct according to the observation that most of the interested acoustic content has energy focused towards the outer walls of the duct. Finally, a hybrid technique combines the earlier approaches by filling the previously neglected space with unstructured mesh. Both the part-span and hybrid methodologies unlock considerable computational savings. Both cases could sufficiently resolve the distorted flow field. The acoustic field at the first two Blade Passing Frequencies (BPFs) was considered for all cases. At the first BPF, both methodologies successfully represent the highest amplitude components. At the second BPF, more deviations were observed for the case that applied the part-span approximation, while the hybrid case results matched well with the datum case
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