Asphalt Concrete Layer Research Articles

Investigation of the Dynamic Stiffness of Poroelastic and Asphalt Concrete Layers under In Situ and Laboratory Conditions.

Compounds with lower dynamic stiffness are a better solution from the tyre/road noise point of view. The article presents the constructed test stand for the evaluation of dynamic stiffness both in in situ and in laboratory conditions. As a result of the tests, it was found that poroelastic pavements have a much lower dynamic stiffness (from 138.3 to 143.0 dB re. 1 N/m) compared to the asphalt concrete pavement (150.3 dB re. 1 N/m). In the group of poroelastic pavements, lower dynamic stiffness is characteristic for pavements with a binder course of porous asphalt. The results of the research are a contribution to further work on the influence of the dynamic stiffness of the pavements on the tyre/road noise level. The conducted measurements and analysis of the results prove the usefulness of the proposed test stand for determining the dynamic stiffness of bituminous mixtures in laboratory and field conditions. This is confirmed by the coherence between the force and acceleration signals at the level of at least 0.96—which indicates a very good validation of the test results with a random error lower than ±5% with 90% confidence level.

Study of the permanent deformation of asphalt mixtures in the field: A multiscale approach

Rutting in asphalt concrete layers is a longitudinal depression in wheel paths caused by traffic load repetitions. Different tests and analysis have been proposed to investigate the phenomenon, although few studies of resistance to rutting can be found regarding a multiscale approach from binder to field in literature. Thus, the main objective of this study is to evaluate the behavior of the different scales against the phenomenon of permanent deformation for different binders, mixtures and in-service pavements, verifying the performance relationship between them and how the properties can be correlated. For this, eight monitored asphalt pavements were chosen during road rehabilitation. They consisted of conventional, SBS modified and rubber binders, evaluated in the laboratory for linear viscoelastic characterization and permanent deformation tests. Track rutting was also observed in the field during the first year for comparison with laboratory results. The experimental segments monitored in this research showed that mixtures with SBS and rubber-modified binders returned lower Rutting/N ratios. It was possible to conclude that binders modified using SBS polymer and rubber have greater stiffness and lower phase angles at high temperatures. Asphalt mixtures showed greater stiffness and lower phase angles at high temperatures for mixtures consisting of binders modified by SBS polymer. Flow Number (FN) results were also higher for these mixtures, suggesting better performance in the field. In the mixture scale, the |E*|/sinφ (54 °C; 1 Hz) show the best correlated-with-field rutting in this research, to binder scale, the Jnr parameter was the one that best represented the behavior observed in the field.

A mass specific volume-based viscoelastic damage model to characterize fatigue damage in asphalt mixtures

Fatigue cracking is one of the most common distresses in flexible pavements, and many damage models have been proposed to predict fatigue cracking, but in these models, the evaluation of damage is related to the choice of the reference configuration, whose subjectivity may lead to subjective evaluation of damage. To describe micro-cracking in asphalt concrete under loading, this paper proposes a new viscoelastic damage model, where damage evolution is connected with the mass specific volume, which is independent of the reference configuration, and the resistance to damage is also represented as an exponential function of mass specific volume to show its decrease under destructive loading. To determine material parameters in the model, nondestructive creep test data are used to obtain the relaxation modulus, and by determining the initial resistance to damage of asphalt concrete with different air voids, the evolution of resistance to damage can be obtained. The rest material parameters can be determined by fitting the destructive test data. To verify the validity of the proposed model, the material behavior under controlled-strain repeated direct tension (RDT) is predicted and the model predictions are compared with test data. It shows and the damage increment in the first loading cycle is largest and the rate of damage increases first and then decreases in each cyclic loading period. In addition, the behavior of the pavement structure under traffic loading is simulated, and fatigue cracking in the asphalt concrete layer of the pavement can be captured by the proposed model. It shows that in thick flexible pavements, both top-down cracking and bottom-up cracking occurs, but top-down cracking is dominant.

Evolution evaluation of high-speed railway asphalt concrete waterproofing layer during laboratory freeze–thaw cycles

An in-depth understanding of internal freeze–thaw damage mechanisms in high-speed railway asphalt concrete waterproofing layer is of great importance to achieve its long-term waterproofing and mechanical performance during the prolonged service life. In this work, four types of composite polymerized railway asphalt mixtures with air voids of 2% were custom-designed and treated with a total of 20 modified freeze–thaw cycles. Meanwhile, the volume and mass measurement, X-ray CT, indirect tensile strength test, and Marshall stability test were used to characterize the internal freeze–thaw damage and evaluate the performance deterioration. The results indicated that the internal deterioration resulted from the generation, expansion, and aggregation of voids and micro-cracks. Meanwhile, a “lag effect” of the freeze–thaw damage, that is, a gradual inward erosion process, was verified by dividing the cylindrical specimens into the core layers, intermediate shell layers, and outer shell layers. The efficiency of the “lag effect” was influenced by the air void content in the outer shell layer, which meant the lower the air void content in the outer shell layer, the slower the freeze–thaw damage. In addition, all four types of asphalt mixtures exhibited promising waterproofing performance and freeze–thaw damage resistance. Binder A and AC-10 mixtures exhibited the superiority in terms of high-temperature performance and freeze–thaw damage resistance based on Marshall stability and flow value that were proved to have adequate efficiency on characterizing the freeze–thaw damage in railway asphalt mixtures.

Mesoscopic asphalt pavement response analysis using a random aggregate generation-based concurrent multiscale method

Asphalt concrete (AC) layers in asphalt pavements are heterogeneous, but they are generally deemed as homogeneous in engineering practice, which cannot realistically reflect the complex mechanical behavior of asphalt pavement, particularly at finer scales. To resolve this problem, the present study developed a random aggregate generation-based concurrent multiscale method to simulate the mechanical response of asphalt pavement using ABAQUS software. In this method, the mesoscopic structure of AC with a 60 cm length was simulated in the vicinity of tire loading by a random aggregate generation method and embedded into a macroscale pavement model. To account for the effects of pavement structure and environmental factors, three thicknesses of AC layer (10 cm, 15 cm and 20 cm), two types of pavement structures respectively with a cement-treated base (CTB) and a granular base (GB), and two pavement temperatures (5 and 35℃) were adopted in the simulation. The maximum principal stress (MPS) values of fine aggregate matrix (FAM) within the region of interest were sorted and the values at the percentiles of 10%, 20%, …, 90%, 100% were extracted. Besides, the number of the elements with top 1% MPS values were evaluated. Specific statistical analysis was performed on these values to investigate potential damage behavior of the AC layer. The results showed that the MPS at the percentile of 100% is at least three times that at the percentile of 90%, which indicates considerable stress concentrations at the narrow gaps between coarse aggregates. Top-down cracking could be the main cracking pattern for the CTB and GB pavement at low temperatures, and bottom-up cracking may be the main damage mode for the GB pavement at high temperatures. Increasing the thickness of the AC layer may effectively reduce the stress level at top of the AC layer for the CTB pavement at low temperatures.

АНАЛІЗ ІСНУЮЧИХ МЕТОДІВ ОЦІНКИ ЯКОСТІ ЗЧЕПЛЕННЯ МІЖ ШАРАМИ ДОРОЖНЬОГО ОДЯГУ

This article is devoted to the study of the quality of adhesion between the asphalt concrete layers of pavement. It is established that the lack of effective methods and appropriate modern equipment or devices does not allow to control the quality of the road structure and affect the composition of the asphalt mixture in the design of pavement in order to improve its technical characteristics. The purpose of the work is to analyze the existing methods, devices and equipment for assessing the quality of adhesion between asphalt concrete layers during shear in the construction of pavement. Research methods - theoretical and experimental. The analysis of the factors influencing interlayer tangential stresses and deformations and leading to loss of stability at shift on highways of Ukraine is carried out. A literature review of data on existing analytical and experimental methods for estimating adhesion during shear between asphalt concrete layers has been carried out. Based on the results of research, taking into account climatic conditions and load parameters from modern vehicles, it is possible to further substantiate the parameters of the optimal method of determining the quality of adhesion between asphalt concrete layers of pavement and develop an automated device to determine it. The results of the work are recommended to be used for quality control during the construction and operation of asphalt concrete layers of pavement. Scope - construction and operation of public roads. Socio-economic efficiency of work is to increase the durability of roads, which will reduce operating costs, increase track stability and road safety. KEY WORDS: ROAD CLOTHES, STRENGTH, ADHESION BETWEEN LAYERS, STRESSSTRAIN STATE, CLIMATE CONDITIONS, TRANSPORT LOADS

ТЕРМОПРУЖНІ ДЕФОРМАЦІЇ АСФАЛЬТОБЕТОННОГО ШАРУ НА МЕТАЛЕВІЙ ПЛИТІ МОСТА ПРИ ЗМІНІ ТОВЩИНИ АСФАЛЬТОБЕТОНУ

Based on the theory of thermoelasticity, the problem of the thermally stressed state of a two-layer fragment of a bridge structure, consisting of a metal base and an asphalt concrete upper layer, is considered under conditions of changing ambient temperature at different values of the asphalt concrete thickness. It is believed that the materials of the layers are characterized by different thermomechanical parameters, which determine the inhomogeneity of the stress and strain fields. It has been established by computer modeling that these factors lead to the concentration of stresses and strains and a change in the stress-strain state of the bridge structure of the driving deck, which is not taken into account in modern practice of designing and operating bridges, and is one of the causes of premature destruction of the asphalt concrete pavement of the road bridge. To eliminate these shortcomings, on the basis of finite element algorithms, a theoretical analysis of the thermally stressed state of a metal orthotropic slab with an asphalt concrete pavement was performed at different ratios of their thicknesses. It is shown that a decrease in the thickness of the upper layer can lead to an increase in the contact and normal tensile stresses initiated in it. Therefore, when designing bridge structures, these features should be taken into account additionally. KEYWORDS: BRIDGE STRUCTURE, ASPHALT-CONCRETE COATING, ORTHOTROPIC PLATE, TRACKED TRACKS, TRANSPORT LOADS, STRESS FIELD, THERMO ELASTIC STATE.

Experimental characterization and two-dimensional hydraulic-hydrologic modelling of the infiltration process through permeable pavements

Permeable pavements are a common solution for wearing course layers in roads and urban areas. They are composed by highly porous materials with permeability several orders of magnitude above of the natural terrain. This work presents, on one hand, the experimental characterisation of the hydraulic behaviour of a permeable asphalt concrete wearing course layer and, on the other hand, the development and validation of a two-dimensional coupled hydraulic-hydrological distributed numerical model to reproduce the effect of the infiltration in the rainfall-runoff transformation and in the overland flow propagation processes. Experiments show linear and potential trends for permeability-hydraulic head relations when considering constant and variable hydraulic heads, respectively, reaching permeability up to 0.04 m/s for 1 m of hydraulic head. Experiments are reproduced numerically by incorporating new infiltration formulas, which consider the infiltration rate as a function of the hydraulic head, and a specific numerical scheme for properly dealing the mass conservation when negative values of the water depth may occur numerically due to high infiltration rates. This two-dimensional coupled hydraulic-hydrological distributed numerical model is a validated tool for simulating the effect of permeable pavements not only in the rainfall-runoff process, but also for the overland flow propagation.

Determination of Minimum Dynamic Modulus (E*) of High Modulus Asphalt Concrete Applied to Semirigid Base Asphalt Pavement

AbstractIn order to mitigate the serious rutting disease of the semirigid base asphalt pavement (SBAP), measuring the settings of a high modulus asphalt concrete (HMAC) layer in the SBAP structure ...

Mechanical Analysis of Preventing Reflection Cracks Based on Stress Absorbing Layer

After asphalt concrete overlay, the reflection crack in the old pavement remains a great challenge. In order to overcome this problem, here, we report the effect of stress absorbing layer on the reflection crack. First, the concrete measures to prevent and reduce reflection cracks at home and abroad are analyzed. Then, the mechanism of the generation and development of reflection cracks is studied, the functional characteristics of stress absorbing layer are analyzed, and the principle of antireflection crack is clarified. Further, the effects of modulus thickness and porosity of stress absorbing layer on the stress of pavement structure layer are discussed. Finally, the effect of the stress absorbing layer on preventing reflective cracks is analyzed by numerical simulation. The analyses show that the stress absorbing layer is a thin asphalt concrete layer with good fatigue resistance and low modulus between the old pavement and asphalt pavement, which delays the expansion of pavement reflection cracks. The stress absorbing layer should have high elasticity and low temperature flexibility, water damage resistance, and interlayer bonding. The simulation results suggest that the modulus of the stress absorbing layer should be 400 MPa∼600 MPa, and the thickness should be 1 cm∼2.5 cm. When the thickness of the stress absorption layer is 2.5 cm, the values of tensile stress σX, equivalent stress σMises and maximum shear stress τMax are 31.7%, 29.2%, and 25.7% lower than those of the layer without addition, respectively. The results demonstrate that the effect of stress reduction is obvious, which plays an important role in preventing or reducing the occurrence of reflective cracks. The designed void ratio of the mixture is between 1% and 2.5% for the indoor permeability resistance test. We believe that these findings have certain guiding significance for theoretical analysis and engineering application of stress absorbing layer.

Numerical investigation of pavement responses under TSD and FWD loading

The Traffic Speed Deflectometer (TSD) overcomes the limitations of the Falling Weight Deflectometer (FWD) in terms of traffic interruption and testing inefficiency, thus has been used for network-level pavement structural evaluation. However, compared to FWD, which has accumulated plenty of data and comprehensive evaluation methods over decades, the applicability of TSD is yet to verify. It is imperative to compare pavement responses under TSD and FWD to validate the applicability and substitutability of TSD. Based on the difference between TSD and FWD in loading characteristics and asphalt concrete (AC) properties, six 3D-Move models were established successively to explore the influence of different testing factors on pavement responses. The simulation results show that under the same load magnitude, peak deflections and peak strains caused by TSD were always greater than that of FWD due to the lower equivalent load frequency of TSD. Compared to the peak deflection, the deflection basin shape of TSD was more sensitive to the dynamic effects and the viscoelasticity of the AC layer. Besides, AC viscoelasticity and damping caused the lag in TSD deflections and strains. In the layer modulus back-calculation from TSD deflections, the dual circular load and dynamic effect of TSD were crucial, but the AC viscoelasticity could be neglected. The use of FWD-based programs to back-calculate the layer modulus from the TSD deflection would result in a stiffer AC layer and a stiffer subgrade.

Mechanical behavior of the asphalt wearing surface on an orthotropic steel bridge deck under cyclic loading

Orthotropic steel decks are prone to fatigue problems and to delamination of the wearing surface. In addition, the mechanical behavior of the asphalt wearing surface on an orthotropic steel bridge deck is viscous and affected by the amplitude and frequency of moving loads. This paper presents an experimental investigation on the strain distribution and evolution in an orthotropic deck under cyclic loading. A five-point bending (5PB) test was used in this study. The tested orthotropic deck was composed of a 14-mm-thick steel plate, an epoxy bonding layer, and a 7-cm-thick epoxy asphalt mixture layer. Two types of tests performed at a fixed temperature were: i) cyclic loading with a small number of cycles at different frequencies and loading amplitudes, and ii) fatigue test. The strain was measured at different positions in the steel plate and in the asphalt wearing course. The results obtained from the first type of tests show the strain distribution in the orthotropic deck and the effect of frequency and loading amplitude on this distribution. When the loading amplitude varied from 20 kN to 40 kN, the behavior of the deck structure was observed to be quasi-linear except for several points in the asphalt wearing course where the strain amplitude was higher than 1000 µm/m. The viscoelastic property of the epoxy asphalt concrete was shown to have a significant influence on the deformation of the deck structure. During the fatigue test, the effect of the cyclic loading on the strain evolution in the orthotropic deck was analyzed. The results show that the accumulated strain in the steel plate was small and reversible while that in the asphalt wearing course was important and irreversible, which caused the cracks and damage in the specimen. Fatigue cracking at the top of the asphalt concrete layer and the debonding of the asphalt concrete layer from the steel plate at the support positions were also observed during the fatigue test.

Effectiveness of the shear strength ratio as an indicator of moisture susceptibility of asphalt mixtures

In this study, the use of shear strength ratio (SSR) in analysing asphalt mixture’s susceptibility to moisture was investigated and verified. Three surface and two base mixtures were considered for the asphalt mixture to be tested. Indirect tensile and uniaxial compressive strength tests were conducted in the laboratory to obtain the mixtures’ shear properties. The SSR in the asphalt concrete (AC) layer was determined for six types of pavement structure with varying asphalt thicknesses. Even though the results of SSR agree with the result of tensile strength ratio (TSR) for the two base mixtures, the SSR values of the three surface mixtures are significantly different while the TSR values are similar, thus, SSR is more sensitive to moisture effect than TSR. Furthermore, the Model Mobile Load Simulator (MMLS3) was conducted on different types of compacted slabs. It was found that the results of MMLS3 and SSR show a good correlation for both surface and base mixtures. This proves the effectiveness of SSR as an indicator for evaluating the moisture susceptibility of asphalt mixtures for the entire AC layer.

Three-dimensional contact stresses of a slick solid rubber tyre on a rigid surface

The main aim of this paper is to quantify the three-dimensional contact stresses imposed by a single slow-moving (or rolling) slick solid rubber tyre on a relatively rough contact surface, such as stiff asphalt concrete or airport concrete surfacing layers. The results indicated the tyre-contact patch of a slick solid rubber tyre to be of rectangular shape for a vertical tyre loading range between 20 kN and 100 kN. The rectangular tyre contact shape was confirmed with static paper prints, as well as an electronically measured contact patch with the stress-in-motion pad device. The study included load calibration using a mass load scale, and a stress-in-motion device. These were used with an existing full-scale accelerated pavement test device, referred to as the heavy vehicle simulator. In addition, simplistic multi-layer linear elastic modelling was used to quantify differences between stress and strain responses of two types of two relatively 'stiff' based pavements, such as an asphalt concrete base and Portland cement concrete base, on similar subbase and subgrade layers. Notable differences were obtained, which could potentially influence further detailed studies on the performance of full-scale slick solid rubber tyres on typical multi-layered pavements.

Influence of incompatibility of thermomechanical parameters of bearing layers of a bridge structure on its thermo-stressed state

On the basis of the theory of thermoelasticity, the problem of the thermally stressed state of a two-layer fragment of a bridge structure, consisting of a metal base and an asphalt-concrete upper layer, under conditions of a change in the ambient temperature at different values of the coefficients of thermal linear expansion of the layers is considered. Using the finite element method, the fields of thermal stresses, deformations and displacements are constructed for various values of the thermomechanical characteristics of the layers. The analysis of the influence of the values of thermomechanical parameters on the stress-strain state of the system is carried out. It is shown that with an increase in the incompatibility of these characteristics, the intensities of stresses and strains increase. The zones of concentration of these functions are found. It is recommended to use materials with close values of their thermomechanical parameters when designing bridges to avoid their premature destruction.

Three-dimensional characterization of bonding features for asphalt pavement interface using a novel interlayer isolation film

Pavement interface bonding largely depends on the interface topography characteristics. This study presents a procedure to characterize the interface bonding features between different types of asphalt concrete layers and reveals the difference of the “interaction effect” between layers. The top and bottom layers of asphalt mixtures were non-destructively separated by a novel interlayer isolation film. An ultra-high-resolution three-dimensional (3D) laser scanner was used to acquire 3D interface data of interlayer. Analysis of variance (ANOVA) was performed to examine the relationship between the damage rate of the interlayer isolation film and its corresponding bonding characteristics. The binary analysis results showed that the damage rate of the isolation film was different due to the asphalt mixture with different gradations in the top and bottom layers. The arithmetic mean curvature (Spc), height distribution skewness (Ssk), and root mean square deviation (Sq) have the most significant effects on the isolation film damage rate at the 99.9 % confidence interval. These characteristics can be used to describe pavement interlayer bonding states. This study provides theoretical support for optimizing the bonding characterization of pavement interfaces.

Numerical Analysis of Reflective Cracking of Continuous Reinforced Composite Pavement under Multifactor Coupling

The occurrence and expansion of reflective cracking is a typical problem associated with the composite pavement that has a proven impact on the life of the continuous reinforced composite pavement. The current research studies a 3D finite element model to preset cracks at the top of the continuously reinforced concrete (CRC) layer’s transverse crack and at the bottom of the asphalt concrete (AC) layer based on the theory of linear elastic fracture mechanics in order to explore the factors responsible for the reflective cracking formation mechanism and expansion law. Considering the main stress parameters that affect the formation of reflective cracking (layer bottom tensile stress and vertical shear stress), the most unfavorable load position and the most unfavorable point of the corresponding stress parameter are determined that are then used to calculate the stress intensity factor of the crack tip under the coupling effect of multiple factors based upon the position and point above the crack, by using the confinement integral. The variance analysis of the stress intensity factor of the crack tip under the multifactor coupling effect is conducted via an orthogonal test in order to determine the main factors affecting the formation and development of reflective cracking. Meanwhile, the analysis of single-factor sensitivity is carried out on all these factors, which reveal the real contribution in the formation and expansion of reflective cracking in the continuous reinforced composite pavement. The results show that the most unfavorable load position for reflective cracking is when the load is on the side of the CRC layer’s lateral crack, while the most unfavorable point of the stress parameter is concentrated within the range of the wheel track. At the same time, analysis of multifactor variance and that of single-factor sensitivity show that the cracking mode of reflective cracking in the continuous reinforced composite pavement is a mixed one, dominated by K2 (slip type), supplemented by K1 (open type), and participated by K3 (tear type), whereas the AC layer’s preset-crack depth ratio, instantaneous temperature drop, and CRC-transverse-crack load transfer capacity are the main factors that affect the formation and development of the reflective cracking. Moreover, a better bonding state between the AC layer and the CRC layer improves the stress intensity factor of the preset crack tip on the bottom of the AC layer.

Temperature features of the asphalt concrete waterproofing layer on high-speed railway in cold regions

The asphalt concrete waterproofing layer (ACWL) has been used as a potential waterproofing structure for the subgrade in Chinese high-speed railway in cold regions. The waterproofing behavior and dynamic response of ACWL have been evaluated in the previously published studies. However, the research on the temperature and thermal stress distribution in ACWL track structure has not yet been studied. This research aims at investigating the strain distribution of ACWL under the temperature influence in winter. The field test was conducted to monitor the strain changes on the ACWL surface under ambient temperature. A 3D numerical model of track structure with ACWL was also developed based on the thermo-mechanical coupled method. The field test results indicated that the longitudinal strain on the ACWL surface changed periodically with the air temperature while the tensile strain increased with the decrease in temperature. The temperature analysis showed that the temperature change inside the track structure caused by the daily temperature change was mainly focused on the depth range from the track slab to the base plate. The maximum negative temperature gradient inside the track slab was reported to occur at 4:00 a.m in winter. The geotextile was further introduced to weaken the bond between the base plate and the ACWL. The calculations proved that the geotextile could effectively reduce the peak tensile strain on the ACWL surface at the joints of the base plates. 1 m − 2 m geotextile was recommended to be placed at both sides of the joint of the base plates.

Automatic Control System of Asphalt Concrete Milling Process Based on Road Milling Machines

Mechanical impact on the upper layers of the road surface with the removal of damaged sections of asphalt concrete surfaces is carried out by specialized Road-Building Machines (RBM) - (cold planer). The capabilities (technical resources) of such RBM have not been fully used. Under these circumstances, a promising area of scientific research is the development and implementation of automatic cold milling process control systems with further improvement of their main functional units and mechanisms. In the article, for the first time, Road Milling Machines (RMM) are represented by a set of interconnected controlled systems, united by the ultimate goal - the removal of asphalt concrete pavement layers corresponding to the thickness of the damaged areas with the further formation of a new pavement, which made it possible to apply the principles of automatic control to the process of milling asphalt concrete pavement by road milling machines.

A Comparison between Static and Repeated Load Test to Predict Asphalt Concrete Rut Depth

Rutting has a significant impact on the pavements' performance. Rutting depth is often used as a parameter to assess the quality of pavements. The Asphalt Institute (AI) design method prescribes a maximum allowable rutting depth of 13mm, whereas the AASHTO design method stipulates a critical serviceability index of 2.5 which is equivalent to an average rutting depth of 15mm. In this research, static and repeated compression tests were performed to evaluate the permanent strain based on (1) the relationship between mix properties (asphalt content and type), and (2) testing temperature. The results indicated that the accumulated plastic strain was higher during the repeated load test than that during the static load tests. Notably, temperature played a major role. The power-law model was used to describe the relationship between the accumulated permanent strain and the number of load repetitions. Furthermore, graphical analysis was performed using VESYS 5W to predict the rut depth for the asphalt concrete layer. The α and µ parameters affected the predicted rut depth significantly. The results show a substantial difference between the two tests, indicating that the repeated load test is more adequate, useful, and accurate when compared with the static load test for the evaluation of the rut depth.