Structural Design Of Asphalt Pavements Research Articles

Research on the Fatigue Life Prediction for a New Modified Asphalt Mixture of a Support Vector Machine Based on Particle Swarm Optimization

SMC (Styreneic Methyl Copolymers) is a novel normal temperature asphalt modifier with superior performance. It has the advantages of a low construction temperature, good road performance, good energy savings and an emission reduction effect, and can improve the performance of an asphalt mixture. The fatigue performance of an asphalt mixture is one of the important technical parameters in the structural design of asphalt pavements. The fatigue performance of an asphalt mixture under specific traffic and environmental conditions has an important guiding significance and normative function for the design, construction, and maintenance of asphalt pavement. In this paper, the mixture of an SMC normal-temperature-modified asphalt and styrene–butadiene styrene block copolymer (SBS)-modified asphalt (SMCSBS) compound-modified asphalt was investigated, and an SMCSBS composite modified asphalt mixture with a different SMC content was prepared. A semi-circular bending fatigue test (SCB) was conducted to analyze and compare the fatigue properties of the modified asphalt mixture. On this basis, this paper proposes a fatigue life prediction model of an SMCSBS composite modified asphalt mixture based on a particle swarm optimization support vector machine (PSO-SVM). SMC content (SMC accounts for the mass percentage of SMCSBS composite modified asphalt)/%, asphalt aggregate ratio, stress ratio and loading frequency/Hz were used as training data to establish the prediction model, and RMSE and R2 were used to evaluate the performance of the model. Experimental results show that the prediction results of the PSO-SVM method are more accurate than the experimental observation data and can effectively improve the prediction accuracy of the model. Compared with the M5′ model tree (M5′), artificial neural network (ANN), and support vector machine (SVM) method, the PSO-SVM method can achieve better prediction performance and a better prediction effect.

Structural Design of Asphalt Pavements in Germany

The motivation for this research comes from the inadequacy of the methods currently used for sizing and optimization of building materials used in pavement construction based on increasing traffic loading and changing climatic conditions. Using examples, the paper highlights how deficits can be identified by a detailed investigation of the relationships in order to form a foundation for solving these deficits.

Characteristics and analysis of the mechanical response inside the structure of asphalt pavement

Determining whether structural analysis method can objectively describe the real service status of pavements is the main issue in the design of asphalt pavements. Given the complexity and variety of pavement materials, the responses of pavement structures under vehicle load and environmental conditions exhibit clear nonlinear characteristics. Obtaining the structural mechanical response characteristics in the course of pavement service is not only the solution to one of the basic issues in the structural design of asphalt pavements, but also the key to ensure the scientific and reasonable analysis of pavement structures. To reveal the structural mechanical response characteristics and change the law of asphalt pavements and provide reliable data for the development of structural design methods that are suitable for the national conditions and highway construction characteristics in China, continuous follow-up observations of the mechanical responses of asphalt pavement structures, such as stress and strain, are conducted using RIOHTrack. The actual service environment and mechanical response law of asphalt pavement structures are obtained using sensor testing technology. The influence law of external factors, such as temperature and load, on the mechanical response behavior is analyzed and the temperature and load dependences of the true mechanical response are revealed. Results show that the structural mechanical response of asphalt pavements exhibits significant temperature and load dependence and that a nonlinear relationship exists between temperature and load. To ensure the rationality of pavement analysis, nonlinear mechanics theory requires consideration in the structural calculations. The stress and strain of asphalt pavements display alternating fluctuations in the annual cycle; the smallest and largest values of the stress and strain at the bottom of the asphalt layer are observed during winter and summer, respectively. For semi-rigid base asphalt pavements, the temperature monotonically affects the value of the mechanical response of the asphalt surface layer and does not change the direction of force. An exponential function can describe the relationship of strain and temperature, whereas the Boltzmann function can describe that of stress and temperature; the decision coefficient R 2 for both functions exceeds 0.94 and therefore indicates good correlation. For full-thick asphalt pavements, the temperature change causes an increase or decrease in the mechanical response values, and a change in direction, that is, compression state and tensile state can switch to each other. And the relationship curve between strain and temperature shows a pull conversion point and a zero strain line. In the depth direction, the compression-tensile conversion occurs between 24–36 cm, and as the temperature increases, the position of the compression-tensile conversion gradually moves down from the surface. The strain response significantly increases with the increase in load level and shows a clear trend of nonlinear change, especially at high temperature and overload. The actual structural mechanical response of the pavement needed to establish the asphalt pavement calculation system and analysis theory is obtained, which addresses the lack of systematic surface structural mechanical response observation test data due to the inability to perform full-scale tests before and provides the basic data for pavement design and analysis. Results can offer theoretical support for polishing the design and analysis methods for asphalt pavements.

Effect of temperature field on damage initiation in asphalt pavement: A microstructure-based multiscale finite element method

The present study developed a microstructure-based multiscale finite element (FE) method to investigate the effect of temperature fields on the damage initiation within the asphalt pavement under traffic loading. Three heat transfer mechanisms that dominate the temperature distribution in the pavement structure, i.e., thermal radiation, convection, and conduction, were considered in the multiscale modeling. Both mechanical and thermal properties of asphalt concrete (AC) on two physical length scales, namely, global (pavement level) and the local (mixture level) scales, were included in the computation and connected via a homogenization process. A digital image processing (DIP) technology was adopted to establish the local-scale representative volume element (RVE) model that interpreted the realistic heterogeneity of the AC microstructure, and a bilinear cohesive zone model was employed to model the damage initiation in the RVEs. The results showed that the developed multiscale FE model provided an insight into the damage behavior of asphalt pavement subjected to temperature fields varying with time on both the global and local scales, indicating the importance of considering temperature fields in pavement structural analysis. By means of the presented method, the influence of temperature fields, pavement structures, mixture microstructures and component properties, and interface behavior between mortar matrix phase and coarse aggregates on the pavement damage initiation could be rationally taken into account in the analysis. In light of these benefits, the presented approach can be expected to be utilized as a mechanistic tool for improving the performance prediction and evaluation as well as mixture and structural design of asphalt pavements.

Test and Analysis on Asphalt Content for Fatigue Performance of Polyester Fiber Asphalt Concrete<sup></sup>

The change law for fatigue properties of polyester fiber asphalt concrete was acquired under different asphalt content by three point bending tests. The results indicate that fatigue life of polyester fiber asphalt concrete increases firstly and then declines with asphalt content increasing, which shows an optimum asphalt content,4.8%. The optimal asphalt content of polyester fiber asphalt concrete is bigger than that of common asphalt concrete. The way to improve fatigue performance of asphalt pavement is found through studying on polyester fiber asphalt concrete. All will provide a theoretical basis for structural design of asphalt pavement.

Mixed-mode fracture characterization of fine aggregate mixtures using semicircular bend fracture test and extended finite element modeling

This paper presents integrated experimental-computational efforts to characterize the mixed-mode fracture of a fine aggregate matrix mixture which is the primary phase of cracks around stiffer coarse aggregates when typical asphalt concrete mixtures are subjected to intermediate service temperatures. Experimentally, semicircular bend fracture tests were conducted by varying the geometric-loading configurations with different initial notch inclination angles and supporting spans to achieve different fracture modes (opening mode-I, in-plane shear mode-II, and mixed). The semicircular bend fracture test results were then integrated with the extended finite element model which is also incorporated with mode-dependent cohesive zone fracture to properly identify the mode-dependent fracture properties. The test and model simulation results indicated that the cohesive zone fracture toughness of in-plane shear mode-II is quite different (approximately three times greater) from opening mode-I fracture toughness. The critical fracture energy was related to the mixed-mode ratio, which presented a power relationship between the total fracture toughness and involvement of in-plane shear mode-II fracture in the total. Findings and observations from this study, although they are limited at this stage, imply that the mixed-mode fracture characteristics are significant and need to be considered in the structural design of asphalt pavements with which multi-axial cracking is usually associated.

Structural Design of Asphalt Pavements: Principles and Practices in Various Design Guidelines

Procedures to perform structural design of pavements are detailed in various design guidelines. Even though the recommendations may be different across the different guidelines, some of the underlying principles are similar. The present paper briefly reviews various pavement design guidelines on structural design of asphalt pavements with reference to the design principles employed. The focus is primarily kept on the mechanistic–empirical pavement design approach. The discussion covers few specific aspects of asphalt pavement design, and does not intend to present an exhaustive treatise on the subject.

Mode-Dependent Fracture Behavior of Asphalt Mixtures with Semicircular Bend Test

Cracking in asphalt concrete pavements causes primary failure in the pavement structure. This cracking is considered one of the key issues to be addressed when paving materials are selected and sustainable pavement structures are designed. Given the diverse nature of traffic loads and pavement geometry, the asphalt mixture in the pavement is subjected to complex cracking behavior, such as mixed-mode fracture (i.e., the combination of an opening mode and a shearing mode of fracture). To date, most studies considered Mode 1 (opening) fractures only, because of technical challenges in testing and analysis. For a better understanding of asphalt fracture and more accurate design of pavement structure, mode-dependent fracture behavior needs to be characterized. This paper presents experimental efforts to characterize the mode-dependent fracture behavior of an asphalt mixture. Toward this end, semicircular bending (SCB) fracture tests were incorporated into the results of digital image correlation analysis for a fine aggregate matrix mixture subjected to a 10 mm/min loading rate and an intermediate temperature condition of 218C. To achieve different fracture modes (i.e., opening, sliding, and mixed), the geometric loading configurations of the SCB test were varied through the use of different initial notch inclination angles and different supporting spans. Test results were further analyzed to calculate fracture resistance. Observations from this study, though limited, imply that mixed-mode fracture characteristics exist and need to be considered in the structural design of asphalt pavements with which multiaxial cracking usually is associated.

Analysis on Mechanical Response for Asphalt Pavement Based on Thickness Variation for Transition Layer of Graded Crushed Rock

The graded crushed rock layers is set between asphalt surface course and semi-rigidity base course to effectively prevent or reduce the reflection crack of semi-rigidity base course and improve the draining condition of asphalt pavement, however, the graded crushed rock is low in modulus and is provided with nonlinearity stress-strain characteristic, and the addition of this transition layer may cause the stress variation of pavement structure. Through applying KENPAVE pavement design program, analyze the mechanical response discipline on pavement structure layer by thickness variation of graded crushed rock layer and put forward the reasonable suggestions for structural design of asphalt pavement for transition layer of graded crushed rock.

Characterization of mode-I and mode-II fracture properties of fine aggregate matrix using a semicircular specimen geometry

Cracking in asphalt pavements causes primary failure in structure, with long-term durability issues often related to moisture damage. Fracture resistance and characteristics of asphalt materials significantly affect asphalt pavement service life. Studies have typically considered only mode-I (opening) fracture, but many observations demonstrate the significance of mode-II (sliding) fracture for better design of pavement structures and damage characterization of asphaltic materials. This study presents experimental and numerical efforts to characterize mode-I and mode-II fracture properties of a fine aggregate matrix mixture. To this end, semicircular bending tests were integrated with a digital image correlation system and extended finite element method. With limited scope and test results, this approach shows that mode-II fracture toughness is quite different from mode-I fracture toughness (approximately three times greater than mode-I), clearly indicating that mode-dependent fracture characteristics are necessary in structural design of asphalt pavements with which multiaxial fracture is usually associated.

Analysis of Influence Factors of Temperature Stress for Open-Graded Large Stone Asphalt Mixes of Asphalt Pavement

The reflective cracking is one of the main damages of semi-rigid base asphalt pavement and rigid base asphalt pavement, how to control its emergence and development is still a major problem for road engineering. At present, researches on mechanical behavior of Open-graded Large Stone asphalt Mixes (OLSM) in China almost remain in the test road observations, very few study it from the point of the finite element theory. Aiming at this problem, a method of using OLSM as the cracking alleviation layer is proposed. The calculation principles of temperature stress of lean concrete base asphalt pavement with OLSM has been introduced, on the basis of the finite element software of ABAQUS, 3-D Finite Element Method (FEM) is used to analyze temperature stress for OLSM of asphalt pavement, the influence rule of pavement design parameters for its temperature stress has been discussed, and the theoretical basis for structural design of asphalt pavement with OLSM has been found.

Modeling mechanistic responses in asphalt pavements under three-dimensional tire-pavement contact pressure

A three dimensional finite element program incorporating actually measured vertical tire-pavement contact pressure (TPCP) was utilized for modeling the mechanistic responses in asphalt concrete (AC) layers by simulating various vehicle motions: stationary and non-stationary (i.e. in acceleration or deceleration mode). Analysis of the results indicated the following items. 1) It is critical to use the vertical TPCP as the design control criteria for the tensile strains at the bottom of the AC layer when the base layer modulus is lower in magnitude (e.g. ≤400 MPa); however, when the base layer modulus is higher in magnitude (e.g. ≥7 000 MPa), the horizontal TPCP and the tensile strains in the X-direction at the surface of the AC layer should also be considered as part of the design response criteria. 2) The definition of “overload” needs to be revised to include tire pressure over-inflation, i.e., a vehicle should be considered to be overloaded if the wheel load exceeds the specification and/or the tire inflation pressure is higher than the specification. 3) Light trucks have more structural impact on the strain responses and pavement design when the thickness of the surfacing AC layer is thinner (e.g. ≤50 mm). 4) The acceleration of a vehicle does not significantly impact the AC surface distresses such as rutting at the top of the upgrade slopes or intersections; however, vehicle deceleration can dramatically induce horizontal shear strains and consequently, aggravate shoving and rutting problems at the highway intersections. Evidently, these factors should be taken into account during mechanistic stress-strain modeling and structural design of asphalt pavements.

Crack Propagation Behavior of Asphalt Concrete; Part II: A Study into Influence of Loading Rates

Cracking has long been accepted as a major mode of premature failure in flexible pavements. Expected life of pavements, pavement condition and maintenance cost are directly related to pavement cracking. It is crucial to have a sufficient understanding of cracking mechanism in order to produce a sound and safe material and structural design of asphalt pavements. Simulation, surveying, observation, and measurement of cracking in pavement structures have been reported in literature in last three decades. However, cracking process in asphalt mixtures in a three dimensional scale is still a great challenge to road engineers. Using SIEMENS SOMATOM plus X-ray CT (computerized tomography) and multi-functional testing rig, a dynamic observation of cracking propagation of hot mix asphalt was conducted in this research. Marshall samples of AC20 were used under uniaxial compressive stress state. Stress and strain behavior was observed during the compressive failure process of asphalt mixtures. Cracking propagation in the samples can be clearly observed and failure mode and stress-strain behavior can then be simulated. Research results show that loading rate is a critical factor influencing cracking velocity and cracking density.

Structural design of asphalt pavement on concrete bridges

Traditional methods for the structural design of pavement cannot be applied to the design of pavement on bridge decks. In this paper, a new method for the structural design of asphalt pavement on concrete bridge decks is presented. The method can be applied to pavement on girder, slab, and box-girder bridges and can be used whatever the considered degree of bonding between pavement and deck. The method consists of modelling the deck as a two-layer system and then calculating stresses and strains in the pavement–deck system by means of a multilayer system. The proposed methodology has been applied to study the behaviour of asphalt concretes, porous asphalts, and stone matrix asphalts on girder, slab, and box-girder bridges. There is a conclusion of this application that stands out for its practical character. The stone matrix asphalts have the best performance if fatigue is the main concern.Key words: bridge decks, asphalt pavement, design.

Structural design of asphalt pavements by computer : Brown, S F; Stock A F; Pell, P S Highway Engr, V27, N3, March 1980, P2–10, 22

The capabilities of a computer program called ADEM for the analytical design of flexible pavements are presented in simple, practical terms. The basis of the computations is explained, together with the distinction between linear and non-linear elasticity. The latter is shown to require more computing time but this may be necessary for pavements with unbound granular bases. The results of several investigations carried out with the aid of ADEM are presented. These include studies of the influence of bituminous mix variables, thickness and quality of sub-base and sub-grade stiffness. The program is shown to produce designs comparable with current practice for standard conditions, but, being fundamentally based, it is applicable to new situations of loading, materials and environment which cannot be solved using empirical methods.(a) (TRRL)