Mechanical Properties Of Asphalt Concrete Research Articles

Static and Dynamic Properties and Temperature Sensitivity of Emulsified Asphalt Concrete

Asphalt concrete is a typical rheological material, which is hard brittle at low temperature and reflects soft plastic facture at high temperature; the temperature has a great influence on the mechanical properties of asphalt concrete. In order to eliminate the environmental pollution caused by hot asphalt construction, cationic emulsified asphalt can be used. This paper transforms the temperature control system for static and dynamic triaxial test equipment, which has achieved static and dynamic properties of emulsified asphalt concrete under different temperatures, and researched the temperature sensitivity of emulsified asphalt concrete materials including static stress‐strain relationship, static strength, dynamic modulus of elasticity, damping ratio, and so on. The results suggest that (1) temperature has a great influence on the triaxial stress‐strain relationship curve of the asphalt concrete. The lower the temperature, the greater the initial tangent modulus of asphalt concrete and the higher the intensity; the more obvious the softening trend, the smaller the failure strain of the specimen and the more obvious the extent of shear dilatancy. When the temperature is below 15.4°C, the temperature sensitivity of the modulus and strength is stronger significantly. (2) With the temperature rising, the asphalt concrete gradually shifts from an elastic state to a viscoelastic state, the dynamic modulus gradually reduces, and the damping ratio increases. When the temperature is above 15.4°C, the temperature sensitivity is obviously stronger for the dynamic elastic modulus and damping ratio. (3) The static and dynamic properties of asphalt concrete are very sensitive to the temperature. The test temperature should be made clear for the static and dynamic tests of asphalt concrete. The specimen temperature and the test ambient temperature must be strictly controlled.

Investigating the mechanical properties of asphalt concrete containing waste polyethylene terephthalate

Reviewing the literature shows that limited work has been conducted on polyethylene terephthalate (PET)-modified asphaltic materials with inconsistent results, missing the investigation of some aspects such as the effect of PET particle size. This paper investigated the effects of waste PET content and particle-size distribution on some engineering properties of asphalt concrete. To this end, Marshall specimens of the mixtures containing different ground waste PET contents of 0%, 2%, 4%, 6%, 8%, and 10% (by the weight of asphalt binder) were subjected to Marshall, indirect tensile strength (ITS), moisture damage, and dynamic creep tests. Two different sizes of PET particles were used: one with particles in the range of 1.18–2.36 mm as coarse-graded PET, and the other with particles in the range of 0.297–0.595 mm, as fine-graded PET. ITS test was conducted on dry and conditioned specimens to evaluate moisture damage susceptibility. Dynamic creep tests were performed under the stress level of 300 kPa at 40°C. Results show that, for both coarse- and fine-graded PET particles, the highest Marshall quotient is achieved at 4% of PET content, after which it decreases with increasing the PET content. Furthermore, results indicate that, for both fine and coarse PET particles, the mixture containing 2% of PET content has the highest ITS and resistance against moisture damage. Based on dynamic creep test results, the resistance against permanent deformation decreases with increasing the PET content. Comparing the results for the mixtures containing coarse and fine PET particles shows that a better performance can be achieved using finer PET particles.

Investigating the Effects of Nanoclay and Nylon Fibers on the Mechanical Properties of Asphalt Concrete

This paper describes the effects of reinforcement by randomly distributed nylon fibers and addition of nanoclay on some engineering properties of a typical asphalt concrete. The properties of asphalt concrete reinforced by different percentages of 25 mm nylon fibers have been compared with those of the mixtures containing different percentages of nanoclay and those in which both the fibers and nanoclay have been included. Engineering properties, including Marshall stability, resilient modulus, dynamic creep and fatigue life have been studied. Nylon fibers have been used in different percentages of 0.1, 0.2, 0.3 and 0.4% (by the weight of total mixture), and nanoclay has been used in 2, 4 and 7% (by the weight of bitumen). It is found that the addition of fibers is more effective than the nanoclay for increasing the resistance against fatigue cracking. However, nanoclay improves the resistance of the mixture against permanent deformation better than the nylon fibers. The results also show that the mixture reinforced by 0.4% of nylon fibers and containing 7% of nanoclay has the highest resilient modulus, Marshall stability and fatigue life. However, the mixture containing only 7% of nanoclay has the highest resistance against permanent deformation.

Correlation Between Aggregate to Aggregate Contact and Mechanical Properties of HMA Mixture

The mechanical properties of hot mix asphalt (HMA) mixture are directly related to the internal structure. Earlier studies have suggested that aggregate-to-aggregate contact maybe a significant contributor to the mechanical properties of HMA mixes. In this study, the mechanical properties of HMA mixture, quantified by Marshall Stability, Flow and Marshall Quotient, were related to the internal structure in terms of aggregate-to-aggregate contact. For development of a model, field core samples were taken from Binder and Topeka layers at different sites. A total of 21 different HMA mixes were obtained. An advanced 2-dimensional Image Processing and Analysis System (i.e., iPas) was used to characterize the internal structure of the cores. The test results indicated that there is a strong correlation between aggregate-to-aggregate contact and mechanical properties of HMA mixture. This is an indication that aggregate-to-aggregate contactis a significant contributor to the mechanical properties of asphalt concrete .

Electrical and mechanical properties of asphalt concrete containing conductive fibers and fillers

Electrically conductive asphalt concrete has the potential to satisfy multifunctional applications. Designing such asphalt concrete needs to balance the electrical and mechanical performance of asphalt concrete. The objective of this study is to design electrically conductive asphalt concrete without compromising on the mechanical properties of asphalt concrete. In order to achieve this goal, various tests have been conducted to investigate the effects of electrically conductive additives (steel fiber and graphite) on the laboratory-measured electrical and mechanical properties of asphalt concrete. The results from this study indicate that the critical embedded steel fiber length is 9.6mm to maximize the fiber’s potential to bridge across the crack from single fiber tensile test. Both steel fiber and graphite can produce conductive asphalt concrete with sufficiently low resistivity, but steel fiber is much more effective than graphite to improve the conductivity of asphalt concrete. A combination of steel fiber and graphite can precisely control the resistivity of asphalt concrete over a wider range. Besides, asphalt concrete containing an optimized amount of steel fibers has a significant improvement in Marshall Stability, rutting resistance, indirect tensile strength, and low temperature cracking resistance compared to the plain concrete. The addition of graphite could increase the permanent deformation resistance with compromised stability and low temperature performance. Asphalt concrete containing steel fibers and graphite weakens the steel fiber reinforcing and toughening effect, but still has a significant improvement in mechanical performance compared to the plain concrete.

Quantification of Aggregate Morphologic Characteristics as Related to Mechanical Properties of Asphalt Concrete with Improved FTI System

AbstractThis paper introduces the improved Fourier transform interferometry (FTI) system, which captures three-dimensional (3D) high-resolution images of aggregates. The improved FTI system uses the two-dimensional (2D) fast Fourier transform (FFT2) to rapidly measure aggregate morphologic characteristics from these images, including sphericity, flatness ratio, elongation ratio, angularity, and surface texture. Eight aggregate fractions, used in two different stone matrix asphalt (SMA) mixtures, were imaged and the calculated aggregate morphologic characteristics were found to be in good agreement with manual measurement results. The influence of aggregate morphologic characteristics on the mechanical performance of asphalt concrete is further examined on mixtures from Culpeper and Staunton in terms of dynamic modulus, flow number, and fatigue performance in laboratory experiments. Experimental results show that the mechanical performance of Staunton asphalt concrete samples was better than that of those ...

Nonlinear modeling and computational homogenization of asphalt concrete on the basis of XRCT scans

This paper provides a methodological framework to investigate the effective mechanical properties of asphalt concrete. We, therefore, use numerical tools based on morphological X-ray Computed Tomography (XRCT) data from asphalt concrete specimens. Asphalt concrete is a multi-component material with spatially varying constituents, but in contrast to many other microstructures used in materials science, the partial microscopic material bulk properties of the constituents of asphalt concrete are accessible by physical testing and, therefore, can be considered as well investigated and known. The information gained by the XRCT is used to create artificial Statistical Volume Elements (SVEs) for our numerical investigations. We apply a discrete particle simulation to generate a densely packed sphere model with a pre-defined particle size distribution (PSD) as a first representation of the mineral filler particles. This model serves as the starting point for a weighted Voronoi diagram. Finally, the volume fractions are adjusted by a stochastic shrinkage process of the Voronoi cells. The artificial microstructures are, a priori, generated in a periodic manner and, therefore, possible boundary layer effects during computational homogenization are minimized. The SVEs are considered to be statistically similar to the real structure and serve as its best possible representation. Besides the SVE generation, this paper focuses on the constitutive description of the bituminous binding agent, which we interpret as a viscoelastic fluid. In our analysis of the results we concentrate on the upscaling properties of morphological and material nonlinearities.

Nano-Mechanical Characterization of Mastic, Aggregate, and Interfacial Zone in Asphalt Composites

Abstract This study used a nanoindentation technique to explore the local nanoscale mechanical properties of material phases and interfaces in an asphalt concrete composite. Regions of aggregate and mastic and their interfaces were nanoindented, and the load-displacement curves were analyzed to calculate the elastic modulus and hardness of the three phases. The interface region was found to have hardness and modulus values between those of the aggregate and the mastic. This study contributes significantly to the nanoscale characterization of asphalt concrete composites, as it provides unique measurements of mechanical properties of phases and especially the interface at a very small scale.

Implementation of a Triaxial Dynamic Modulus Master Curve in Finite-Element Modeling of Asphalt Pavements

The newly developed Mechanistic-Empirical Pavement Design Guide (MEPDG) uses the dynamic modulus master curve to account for the temperature and frequency dependent behavior of asphalt concrete. However, the master curve used in the MEPDG is constructed using dynamic moduli measured in uniaxial testing and the effect of confinement on the mechanical properties of asphalt concrete is disregarded. This study implemented a model of triaxial dynamic modulus master curve in finite-element (FE) modeling of asphalt pavements. The dynamic modulus distribution in asphalt layers due to the contribution of confinement was evaluated for various scenarios. The results show that when the effect of confinement is considered the dynamic modulus can be more than two times the uniaxial value at the same temperature and frequency. The effect of confinement on dynamic modulus is more evident at high temperatures and low frequencies. Various pavement responses were computed using the developed FE model and compared to those obtained using the corresponding uniaxial dynamic modulus. For the pavements analyzed in this study, the confinement has the most pronounced effect on the permanent deformation of asphalt layers. The compressive strain in asphalt layers can be reduced to about half of the value obtained using the uniaxial dynamic modulus.

Correlation between Shape of Aggregate and Mechanical Properties of Asphalt Concrete

Correlation between Shape of Aggregate and Mechanical Properties of Asphalt Concrete

Modulus prediction of asphalt concrete with imperfect bonding between aggregate–asphalt mastic

Asphalt concrete (AC) is a kind of complex multi-phase engineering material. To date, the evaluation and determination of mechanical behavior of AC remain resorting to experiments. However, this approach is not able to directly reveal the influence of the microstructure of AC quantitatively. In this paper, a micromechanics-based model is described to simulate the elastic behavior of AC, with the emphasis on the influence of the interfacial zone on the overall mechanical properties of AC. Tests on asphalt mixture with varying microstructures are conducted to verify the proposed model. The effect of key factors on the behavior of AC is investigated, including the modulus of asphalt mastic and coarse aggregate, air void fraction, aggregate gradations, the largest aggregate and interface between asphalt mastic and coarse aggregates. The outcome resulting from this paper can be applied to guiding the design efficiently to obtain different functional AC.

Correlation between Shape of Aggregate and Mechanical Properties of Asphalt Concrete

ABSTRACT The importance of the shape of aggregate particles on their mechanical behavior of bituminous materials is well recognized. In asphalt concrete, the shape of aggregate particles affects the durability, workability, shear resistance, tensile strength, stiffness, fatigue response, and optimum binder content of the mixture. In recent years, DIP techniques are widely used to analyze the shape indexes of aggregate. In this study, the shape characteristics such as aspect ratio, elongation, flatness, form factor, roundness, shape factor, and sphericity were determined by DIP technique. The coarse aggregate was proportioned into three size fractions, namely, 19 to 12.5 mm, 12.5 to 9.5 mm, and 9.5 to 4.75 mm. Coarse Aggregate sizes of 19 to 12.5 mm and 12.5 to 9.5 mm were selected by hand as three categories of flat, elongated, and spherical. In addition, a control mixture containing all of aggregate shapes was prepared. ImageJ Java program was used as the image analysis program. This program measures a lot of geometrical values such as area, perimeter, length and angle. Asphalt concrete specimens were fabricated in accordance with ASTM D 1559. Marshall stability and flow values were determined and volumetric properties of all Marshall specimens were calculated. The test results indicated that there is a good correlation between some shape indexes of aggregate and asphalt concrete properties. The DIP was shown to be a useful tool for quantifying the morphological characteristics of coarse aggregates. Therefore, DIP technique proposed in this study may be used instead of some mechanical asphalt concrete tests which are cumbersome and time consuming. However, further studies may lead to use the DIP technique in aggregate quality assurance and quality control procedures and stability and flow values for HMA concrete can be predicted using DIP. It should also be pointed out that further studies on the image analysis system are needed to make more useful and practical method for DIP.

Effects of Conductive Fillers on the Dynamic Response and Fatigue life of Conductive Asphalt Concrete

It is currently interesting to use thermal or electrical conductive asphalt concrete for snow-melting and maintenance of asphalt pavements in winter. The addition of conductive fillers may have negative effects on the mechanical properties of asphalt concrete. The performance of conductive asphalt concrete is greatly affected by the initial crack and its propagation. Laboratory tests for neat and conductive asphalt concrete include Dynamic Modulus Test (DMT) and Indirect Tensile Fatigue Test (ITFT). DMT tests indicates that the value of dynamic modulus of asphalt concrete decreases with the increasing graphite content. It means that the conductive asphalt concrete achieves lower stiffness. It can be concluded from ITFT tests that the fatigue life (load cycle times) of conductive asphalt concrete is more than neat ones when stress level is under 1.0 MPa. Meanwhile higher fatigue resistance of conductive asphalt concrete is observed when carbon fibers (2 weight % of total aggregate) were added together with 22% graphite, especially at low stress levels.

Application of Mixture Theory in the Evaluation of Mechanical Properties of Asphalt Concrete

Asphalt concrete is a heterogeneous mixture of three constituents of asphalt binder, aggregate, and air void. The local volume fractions of these constituents vary spatially and therefore result in the spatial gradients of the local volume fractions. The local volume fractions and their spatial gradients are important field variables in mixture theory that predicts the mixture behavior out of the structure of the mixture and the properties of the constituents. In this paper, the fundamentals of mixture theory and a general method for solving boundary value problems using mixture theories were presented. A simplified mixture theory for two-constituent mixtures of solids and air voids was proposed to model the initial stress distribution of asphalt concrete under static loading. The analytical solutions of simple two-dimensional (2D) and one-dimensional (1D) cases using the simplified theory were obtained to illustrate how this theory predicts the effective stress distribution of a heterogeneous mixture. Methods to quantify the two field variables of the mixture theory, namely the local void volume fraction and its gradient, are developed using x-ray tomography imaging. The quantified void local volume fraction and its gradient for the specimens of mixes with known performance indicated a promising perspective for using mixture theory to evaluate the mechanical properties of asphalt concrete.

Relationship between the Representative Volume Element and Mechanical Properties of Asphalt Concrete

The size of an asphalt concrete test specimen has been traditionally determined based on experience and practical purposes. This study discusses theoretical considerations for selecting the minimum dimensions so that the resulting size of the specimen represents global material properties. The ideal size of the specimen was determined using an image analysis approach and was verified with mechanical tests. The image analysis was accomplished by studying the internal structure of asphalt concrete. The internal structure was captured using a nondestructive X-ray computer tomography technique. Mechanical testing was accomplished by using the Superpave Shear Tester on laboratory-prepared samples. The laboratory samples had dimensions that were both smaller and larger than the theoretically determined representative size. Statistical analysis indicates that the variability of the results is a function of the loading mechanism used in the Superpave Shear Tester. In general, the required representative size increased considerably when the nominal aggregate size was larger than 25.0 mm.

Relation of HP‐GPC Profile with Mechanical Properties of AC Mixtures

This paper presents an experimental analysis of the relationship between the relative quantity of a particular‐size molecule in asphalt cement and the mechanical properties of asphalt concrete. Three AC‐20 grade asphalt cements (AC) and recovered asphalt cements from four sources were used for high pressure‐gel permeation chromatography (HP‐GPC) testing and for preparing asphalt‐concrete mixtures. Specimens of laboratory‐prepared asphalt concrete and field cores were tested for tensile strength and resilient modulus in dry and wet conditions. Multiple‐regression analyses indicate that tensile strength and resilient modulus had significant correlations with certain areas of chromatograms that are divided into 10 slices. Tensile strength appears to be sensitive to variation of the relative areas of the second and third slices (T2+T3) and resilient modulus vary with the area of the first, second, and third slices (T1+T2+T3). In general, higher relative quantity of larger size molecules cause lower tensile st...