Asphalt Concrete Structure Research Articles

A coupled thermo-hydro-mechanical framework for simulating the failure response of asphalt concrete under freezing conditions

Freezing-induced damage occurs in extremely cold regions in the form of sudden and simultaneous formation of cracks in dry and wet asphalt concrete. This work investigates the mechanical response, up to and including final failure, of dry and partially saturated asphalt concrete at freezing temperatures as low as −30° (−22 °F). A coupled thermo-hydro-mechanical constitutive framework is proposed within the context of finite element simulation. The framework contains nonlinear viscoelastic-viscodamage constitutive equations, the swelling strain effect associated with the freezing of water content, and the moisture damage constitutive equation. The stress induced in dry and partially saturated asphalt concrete samples due to reducing temperatures is simulated and compared with those of a studied experiment, and an excellent agreement is achieved in terms of the critical features, including the final brittle failure and the swelling effect. A parametric study is then performed to discover the effects of the microstructural constituents of asphalt concrete on its mechanical response under freezing conditions. This work provides a reliable computational framework that can predict deterioration and damage in asphalt concrete structures in extremely cold weather and further leads to the development of novel construction materials that can resist the negative effects of cold temperatures, e.g., in the Arctic.

Theoretical Background of Self-Healing in Asphalt Concrete

The article presents theoretical premises that can be used to describe the mechanism of self-healing of the state of the structure of asphalt concrete containing an encapsulated reducing agent. The article presents the main provisions of the Flory-Huggins theory, according to which the restorative effect can be realized due to the ability of organic binder molecules to spontaneously entangle with each other. The intensity of this process depends on the proximity of the molecules to each other and the rate of spontaneous motion, which increases with increasing temperature. And in accordance with the theory of adhesion, the restoration of the state of the structure of asphalt concrete can be due to the mechanisms of formation of adhesive bonds with the help of an encapsulated modifier. To describe the features of the formation of adhesive bonds during restoration, the approaches described in the mechanical, molecular, chemical, diffuse, relaxation theory of adhesion or the theory of weak boundary layers can be used.

Theoretical modelling of the effect of thermal delamination of an asphalt concrete pavement from a rigid foundation of a road or bridge

In the practice of road construction, one of the most common phenomena accompanied by delamination, subsequent cracking and destruction of the asphalt concrete pavement on a rigid (cement concrete or metal) base of a road or bridge is the effect of concentration of shear thermal stresses between the pavement and the base in the edge zones of the structure. They are caused by the fact that, as a rule, the coefficients of linear thermal expansion of the phases of the system have different values, which contributes to the occurrence of incompatible shrinkages and expansions in them. Under conditions of frequent temperature changes in heterogeneous asphalt concrete structures with thermomechanical incompatibility of their components, these effects can contribute to their accelerated aging. At the same time, with the thermomechanical compatibility of materials, a more favorable distribution of internal stresses of thermal and mechanical origin is achieved, which excludes premature degradation of the strength of the contacting phases and the entire system as a whole. Using the methods of strengthof materials and the finite element method, it has been established that under the conditions of a change in the temperature of the system during its seasonal and daily fluctuations, shear stresses are subjected to the highest concentration. They are localized in the edge zone of the plane of contact between the layers and increase with an increase in the thickness and modulus of elasticity of the upper layer. These stresses are the main reason for the occurrence of plastic deformations in these zones and subsequent delamination of the structure in them. It is proposed to reduce the concentration and level of generated high-gradient shear stresses by reducing the thickness of the asphalt concrete layer in these areas.

Numerical Investigation of Asphalt Concrete Fracture Based on Heterogeneous Structure and Cohesive Zone Model

The fracture behavior of asphalt concrete is closely related to its internal structure. A deep understanding of the relationship between the internal structure and fracture behavior of asphalt concrete is very important for sustainable and durable pavement design. In this paper, a CZM-based FE model was developed to investigate the fracture behavior of asphalt concrete. An image-aided approach was used to generate the 3-D internal heterogeneous structure of asphalt concrete. A series of 2-D cross sections were extracted from the 3-D structure for finite element modeling. Then numerical simulations of SCB tests were conducted and validated with experimental results. With the validated CZM-based FE model, the effects of some critical factors, including temperature, loading rate, aggregate geometry, fracture strength, and fracture energy, on the fracture behavior of asphalt concrete were investigated. The analysis results showed that the average damage of the adhesive elements was higher than that of the cohesive elements at the peak load. At lower temperatures, asphalt concrete tends to crack earlier, and the cracking path tends to be marginally closer to the aggregates. A higher loading rate may induce more, but minor, element damage since the CZM elements in asphalt mortar cannot bear much more stress through deformation. Angular aggregates may induce a higher percentage of damaged elements, especially adhesive-damaged elements. On average, each 10% increase in fracture energy allows the specimen to bear 2.31% more load and 2.82% more displacement. Sufficient fracture energy could improve the ability of asphalt concrete to resist fracture.

A cohesive viscoelastic-elastoplastic-damage model for DEM and its applications to predict the rate- and time-dependent behaviour of asphalt concretes

Asphalt concrete is a composite heterogeneous material comprised of aggregates bonded together by bitumen binder. The mechanical behaviour of this material shows great dependence on loading rates and time (e.g., creep, relaxation). Such heterogeneity in the internal structure and complex behaviour of asphalt concrete present a challenge for numerical methods to fully capture its responses under different loading rates and durations, especially when large deformation and crack development are present in the material. This study proposes a modelling approach capable of capturing the behaviour of asphalt concrete under different loading rates and durations. In this approach, the heterogeneous internal structure of asphalt concrete is naturally reproduced by the discrete element method (DEM). In parallel, a new inter-particle contact model is developed for the DEM to describe the grain-level behaviour of asphalt concrete. This contact model couples a viscoelastic-damage law with a cohesive-elastoplastic-damage law, enabling the contact model to characterise the rate and time dependency, viscoelastic damage, and plastic-damage behaviour of asphalt concrete. Moreover, thanks to the use of DEM, the proposed approach can naturally capture crack initiation and development. Through comparisons and verifications with a wide range of experiments on asphalt concrete, including the relaxation test, creep test, and dynamic semi-circular bending test, the proposed approach shows its capability of overcoming the limitations of previous DEM models in reproducing the complex behaviours of asphalt material under various loading conditions. Insights into the failure mechanisms of asphalt material under complex loading conditions and its transitional behaviours from diffuse to localised failure can be thus naturally derived from the proposed DEM approach. This study demonstrates the effectiveness of the proposed approach for investigating the behaviour of asphalt concrete.

Mechanical properties of track-asphalt concrete-subgrade bed structure system under both temperature and train loading

Asphalt concrete has good viscoelasticity, impermeability and durability, which is very suitable for the requirements of high-speed railway substructure. The stress and deformation characteristics of track-asphalt concrete-subgrade system under periodic temperature and train loading were studied. The results indicate that the fatigue life of asphalt concrete structure is much longer than the actual number of train actions. The temperature effect is the main reason for forced tension of asphalt concrete layer at the base plate joints. Laying 1.2 m composite geomembrane on both sides of structural joint can reduce the tensile strain by 60% and effectively improve the stress state.

The use of waste in the composition of organic-mineral mixtures used in road construction

The construction of highways requires a large amount of building materials. Organo-mineral mixtures, which include asphalt concrete, are the main building material for the construction of the upper layers of the road structure. In order to reduce the cost of asphalt concrete, part of the natural mineral raw materials may be replaced by industrial waste. Previous studies show that waste from various industries in terms of their physical and mechanical properties are not inferior to natural raw materials used in road construction. When using the material resource of waste, environmental issues are additionally resolved by reducing the volume of waste disposal at landfills. The studies carried out have shown that the composition of the asphalt concrete mixture, in which drill cuttings are used, as a mineral powder, meet the requirements for asphalt concrete. Studies have shown that waste plastics HDPE and LDPE can be considered as reinforcing and modifying elements in the structure of asphalt concrete. Asphalt concrete, which includes plastic waste, meets the requirements for asphalt concrete used for road construction.

Optimum Study of Electric Electrode of Conductive Asphalt Snowmelt Pavement Based on the Melting Effect

The design and optimization of electrode is the key work in the design of conductive asphalt concrete structure. On the basis of preliminary experimental research, two most representative electrode forms were selected for influencing factor analysis and optimization scheme design. Then the distance, length and material of electrodes were changed respectively to compare the snowmelt effect of conductive asphalt specimens. The optimization results demonstrate that copper is selected as the electrode material, considering the cost and the influence of the later stage on the pavement performance, single beam copper electrode is recommended as the best electrode form, with spacing of 4cm and the heating effect of asphalt pavement is the best. The relevant research results provide data reference for the engineering application of conductive asphalt concrete.

ИССЛЕДОВАНИЕ БИТУМНО-ВЕРМИКУЛИТОВЫХ МАСТИК И АСФАЛЬТОБЕИОНОВ ДЛЯ ДОРОЖНОГО СТРОИТЕЛЬСТВА

В работе исследованы битумно-вермикулитовые композиции, мастики и асфальтобетонные смеси, предназначенные для дорожного строительства. Проведены исследования по получению и испытаниям битумно-вермикулитовых композиций с использованием битумов нефтяных дорожных марок БНД 90/130 и БНД 60/90 и вспученного вермикулитового песка фр. 0,6 – 1,0 мм. Разработаны и испытаны в дорожных условиях битумно-вермикулитовые мастики, асфальтобетонные смеси (по ГОСТ 9128) и показана их эффективность при ремонте асфальтобетонных покрытий в условиях эксплуатации автомобильных дорог на севере Тюменской области.

ИЗМЕНЕНИЕ СВОЙСТВ АСФАЛЬТОБЕТОНА ПРИ ИСПОЛЬЗОВАНИИ ГИДРОФОБИЗИРОВАННОГО МИНЕРАЛЬНОГО ПОРОШКА

One of the main factors is the structure of asphalt concrete. The most important structural component in asphalt concrete is mineral powder, the quality of which depends on the technical and operational characteristics of the road surface. Different methods of processing mineral materials are used to improve the performance of asphalt concrete in Russia and abroad. In most cases, mechanical activation with organic substances is used during the grinding process.
 The article presents the results of research on the effect of treatment of mineral powder with the preparation GF-1 on its characteristics and on changes in the physical and mechanical properties of asphalt concrete, as well as on indicators for long-term water saturation. 
 It is shown that as a result of modification, the mineral powder becomes hydrophobic, which has a positive effect on the physical and mechanical characteristics of asphalt concrete with its use. It is found that hydrophobization of mineral powder significantly reduces water saturation and swelling; increases water resistance during long-term water saturation (up to 90 days) of asphalt concrete samples. As a result of hydrophobization, the temperature sensitivity of asphalt concrete increases significantly. Therefore, the composite will work reliably in a wider temperature range.

Using Steel-Smelting Slag as a Raw Material Component in the Production of Asphalt Concrete

The possibility of using polydisperse steel-smelting slag for the production of type B asphalt concrete is investigated, the possibility of its use as a mineral powder, crushing screening and crushed stone is considered. As a result of the study, it was found that a promising area for the use of slag raw materials in the technology for the preparation of asphalt mixes is: as a mineral powder - without additional processing steps; crushing screening - with the development of additional technological operations. The use of raw materials as crushed stone is impractical because of the high average density of the final asphalt mixture. Based on the test results, the characteristics of the fatigue properties of asphalt concrete from fine-grained dense mixtures of type B made on mineral powders from slag and limestone were obtained. It was established that at the initial moment, a large number of cycles to failure are characterized by compositions on slag powder, however, samples from this series tested after 45 days showed a significant rigidity increase and were destroyed earlier than similar samples on limestone. Obviously, this phenomenon is associated with an increase in the brittle properties of the material due to the formation of crystallization-condensation bonds in the structure of asphalt concrete containing slag.

Reduced order modeling of viscoelastic properties of asphalt concrete

AbstractBiphasic asphalt concrete consists of mineral aggregates and a surrounding bituminous binding agent, of those material properties are known. To obtain the overall material behavior, we generate Statistical Volume Elements (SVE) of the asphalt concrete structure artificially. Afterwards, the Nonuniform Transformation Field Analysis (NTFA) is applied to homogenize them. This paper focuses on the stochastical differences of the microstructures of the SVEs and their influences on the macroscopic material behavior. Therefore, an indirect tensile test is simulated.

Effect of tack coat dosage and temperature on the interface shear properties of asphalt layers bonded with emulsified asphalt binders

The shear strength of the interface of asphalt concrete structure has a great influence on the mechanical properties and durability of asphalt pavement. This paper describes the experimental design and analysis of the shear properties of the interface between asphalt layers. A self-designed device was employed to measure the direct shear strength of the interface with the aid of the Universal Test Machine (UTM-100). The effect of temperature, dosage of tack coat and type of tack coat on the shear properties of the interface were studied through laboratory testing. Two types of emulsified asphalt binders, namely PC-3 and HV, were selected as the tack coats. The property was evaluated in three tack coat dosages (0.25Kg/m2, 0.5Kg/m2 and 0.75Kg/m2 based on residual binder) and at four test temperatures (−10°C, 0°C, 25°C and 50°C). Hence, a total number of 72 composite specimens made of AC-13 and AC-20 were subjected to the shear test to evaluate the interface shear characteristics in terms of interface shear strength, the shear failure displacement and the coefficient of interface bonding at the initial stage of shear. The results showed that the shear strength at the interface decreases gradually with increasing temperature. The least failure shear displacement of all specimens was observed at the highest temperature of 50°C. Moreover, the results indicated that the brittleness at low temperatures, the flowability at intermediate temperatures, and the viscosity at high temperatures of tack binder have the most significant effects on the shear property of the interface of asphalt pavement.

Numerical Study on the Asphalt Concrete Structure for Blast and Impact Load Using the Karagozian and Case Concrete Model

The behaviour of an asphalt concrete structure subjected to severe loading, such as blast and impact loadings, is becoming critical for safety and anti-terrorist reasons. With the development of high-speed computational capabilities, it is possible to carry out the numerical simulation of an asphalt concrete structure subjected to blast or impact loading. In the simulation, the constitutive model plays a key role as the model defines the essential physical mechanisms of the material under different stress and loading conditions. In this paper, the key features of the Karagozian and Case concrete model (KCC) adopted in LSDYNA are evaluated and discussed. The formulations of the strength surfaces and the damage factor in the KCC model are verified. Both static and dynamic tests are used to determine the parameters of asphalt concrete in the KCC model. The modified damage factor is proposed to represent the higher failure strain that can improve the simulation of the behaviour of AC material. Furthermore, a series test of the asphalt concrete structure subjected to blast and impact loadings is conducted and simulated by using the KCC model. The simulation results are then compared with those from both field and laboratory tests. The results show that the use of the KCC model to simulate asphalt concrete structures can reproduce similar results as the field and laboratory test.

Evaluation of in situ RAP binder interaction in asphalt mastics using micromechanical models

In this article the mastic level structure of asphalt concrete containing reclaimed asphalt pavement (RAP) materials is investigated using the principles of micromechanics. Locally sourced RAP material was screened and sieved to separate the coated fines (smaller than 0.075 mm) from the remaining sizes. These binder coated fines were mixed with virgin filler at proportions commensurate with 0, 10, 30, 50 and 100% RAP dosage levels. Asphalt mastics were prepared with these blended fillers and a PG 64-22 binder at a filler content of 27% by volume. Temperature–frequency sweeps were conducted on the resulting composites as well as the constituents, virgin binder, solvent extracted RAP binder. The results from the experiments showed an expected increase in stiffness with increase in dosage levels. These results were also used to model the hypothesised structure of the composite. The study presented discusses the applicability of Herve and Zaoui model to predict the blended mastic composite and to quantify the amount of blending between RAP binder and newly added asphalt binder. It is found that as the RAP dosage level increases the amount of blending that occurs, as a proportion of the total RAP binder decreases.

하모니 검색 알고리즘을 이용한 피로균열의 포장설계 및 유지보수 시기 결정

PURPOSES : This research describes how to predict the life cycles of fatigue cracking based on NCHRP Report 704 as well as modified harmony search (MHS) algorithm. METHODS : The fatigue cracking regression model of NCHRP Report 704 was used in order to calculate the ESAL (Equivalent Single Axle Load) numbers up to pavement failure, based on using material parameters, composite modulus, and surface pavement thickness. Furthermore, the MHS algorithm was implemented to find appropriate material parameters and other structural conditions given the number of ESALs, which is related to pavement service life. RESULTS : The case studies show that the material and structural parameters can be obtained, resulting in satisfying the failure endurance of asphalt concrete structure, given the number of ESALs. For example, the required ESALs such as one or two millions are targeted to satisfy the service performance of asphalt concrete pavements in this study. CONCLUSIONS : According to the case studies, It can be concluded that the MHS algorithm provides a good tool of optimization problems in terms of minimizing the difference between the required service cycles, which is a given value, and the calculated service cycles, which is obtained from the fatigue cracking regression model.

Soft Asphalt Pavement – Solution for Low-Volume Roads in Changing Climate and Economy

In Lithuania, it has always has been an important issue to find durable and cost-effective solutions for paving low-volume roads. The conventional asphalt concrete structures were built using paving grade bitumen with the penetration of 70/100 or 100/150 over the recent 20 years. The performance of those pavements was satisfactory. As an alternative solution, the use of soft asphalt pavements was proposed. This technology is widely used in Nordic countries. But in Lithuania it has never been applied. Research on the designed soft asphalt mixtures was carried out and the trial on-site sections were constructed. The results of laboratory tests and on-site research were positive and promising. Based on that, the technology could be considered as successfully implemented and good quality was achieved.

실험계획법 및 하모니 검색 알고리즘을 이용한 아스팔트 포장체의 피로균열 공용성 관련 인장변형률 추정모델 연구

This research describes how to predict a model of the tensile strain related to the fatigue cracking performance of several asphalt concrete structures through design of experiments(e.g., Response Surface Methodology) and harmony search(HS) algorithm. The axisymmetric analysis program of finite element method, which is the KICTPAVE, was used to determine the strain level at the interface layer between asphalt layer and lean concrete layer. Once the training database set of various strain levels was constructed under the several condition of layer stiffnesses and thicknesses in the asphalt concrete structures, the data set was trained through the HS algorithm in order to determine the regression coefficients defined based on a response surface methodology. Furthermore, the testing set, which was not used for the training procedure of HS algorithm, was also constructed in order to evaluate whether the regression coefficients of a prediction model can be appropriately applied for other cases in asphalt concrete structures.

Characterising the aggregate structure variations in asphalt concrete during compaction using computer automated imaging techniques

The internal structure of Asphalt Concrete (AC) mixes, which refers to the content and the spatial and directional distribution of air-voids, aggregates and asphalt, evolves during the process of compaction which is an important step in the construction of AC pavements. During the process of compaction, aggregates coated with asphalt are brought together by pressure and kneading action while reducing the volume of air trapped within it. This study focused on applying computer automated imaging techniques and near-neighbour distance methods to quantify the variation in inter-particle distances and areas during the process of laboratory compaction of AC.

INFLUENCE OF HOMOGENEITY OF MINERAL MATERIALS' GRADING AND DOSING ERRORS ON THE STABILITY OF ASPHALT CONCRETE MIXTURE COMPOSITION

Errors of optimal composition asphalt concrete mixture designed in the laboratory and their importance for road construction are investigated. After the analysis of asphalt concrete production according to the traditional technology, factors influencing its structure, characteristics and quality are systematised. Mathematical models of dependence of medium quadratic deviations of siftings of finite dosed mineral materials through control sieves on the means of siftings are estimated by a regressive analysis. Variations of grading of hot fractions 0–5 mm and 5–15 mm as well as cold mineral powder sieved through technological sieves of mixing equipment and influence of errors of dosing these mineral materials in the produced mixture on the stability of quantity of containing mineral components (crushed stone, sand and mineral filler) are identified. The main trends of asphalt concrete structure and handling of its equipment methods improvement are presented.