Papers by Keyword: Complex Shear Modulus

Abstract: In this study, Dynamic Shear Rheometer (DSR) and Fourier Transform Infrared (FTIR) spectroscopy tests were performed on 35-50 and 70-100 penetration-graded asphalts. Both tests were performed on specimens at three different ageing states: unaged, short-term aged using the standard rolling thin film oven (RTFO) device, and long term aged by placing RTFO residue in the pressure aging vessel (PAV) apparatus. The tests were accomplished to quantify how ageing affects the results of both tests, namely the complex shear modulus for the DSR test and the carbonyl, sulfoxide, and ageing indices for the FTIR spectroscopy test. Both sets of measurements confirm that the harder asphalt stays harder than the softer asphalt after undergoing ageing, but the rate of hardness is higher for the softer asphalt. For instance, on average, PAV ageing was found to increase the amplitude of the shear complex modulus, from the unaged state, by 4.3 times and by 6.2 times for the 35-50 and 70-100 asphalts, respectively. It was also found that ageing decreases the phase angle for asphalt and the decrease is more pronounced for the softer asphalt (70-100) than the harder one (35-50). This was attributed to more maltenes content in the softer asphalt that transform into asphaltenes during ageing. Correlation coefficient between FTIR signals from the same samples revealed that FTIR spectroscopy as used in this research has an excellent repeatability. The repeatability was also confirmed using measures of dispersion such as the coefficient of variation, which was found not to exceed the 1.2%. The 35-50 asphalt was found to have more C=O and S=O links than the 70-100 asphalt since it showed more absorbance in the carbonyl and sulfoxide bands. These links are thought to make the asphalt physically harder. An analysis of variance study revealed that ageing is a statistically significant factor as measured using ageing indices calculated from FTIR spectroscopy data with the index AI_FTIR being the most sensitive to ageing among all considered indices. Empirical power equations with high coefficient of determination values were established to predict DSR results from FTIR index values, which was possible since both types of measurements show the same trend with ageing.

Abstract: The work deals with the detection of presence of RAP (reclaimed asphalt pavement) in asphalt mixtures. Information about the presence of RAP in an asphalt layer can be technically advantageous, for example, when planning further recycling of the layer. The method described in the paper can also be used to verify the success of a treatment of an aged binder in RAP, which is dosed in the production of new asphalt mixtures. The asphalt binder was obtained by a method of successive extraction from asphalt mixtures with different RAP content. Basic empirical tests of the asphalt binder (needle penetration and softening point) were chosen to detect the presence of RAP. The complex shear modulus G* was further determined on the extracted binders using a dynamic shear rheometer (DSR).

Abstract: In sustainable asphalt pavement construction, the proper selection of materials can be a challenging task. This paper focuses on a newly developed asphalt modifier named calcium carbonate (CaCO₃) combined with Treated Palm Oil Fly Ash (TPOFA) to improve the properties of asphalt mastic. The rheological properties of mastic in terms of penetration, softening point, rotational viscosity and Superpave rutting factor using 60/70 asphalt binder blended with 5, 10, 15, 20 % of CaCO₃+TPOFA were calculated to evaluate asphalt binder properties subjected to different aging conditions. The rotational viscometer (RV) was used to evaluate the properties of mastic at test temperatures from 120°C to 170°C. The dynamic shear rheometer (DSR) was used in temperature sweep test from 46°C to 82°C at 6°C increments at 10 rad/sec frequency to measure the G*, δ and Superpave rutting factor G*/sinδ. A one-way ANOVA statistical analysis was used to analyze the results .The test results showed that all asphalt mastic exhibited higher viscosity compared to the base binder. The addition of CaCO₃ +TPOFA increased the G* but reduced the phase angle which indicated improved stiffness of asphalt mastic. Hence, incorporating CaCO₃+TPOFA can potentially improve the rutting resistance of asphalt mastic.

Abstract: The paper presents the procedure of identification of a complex shear modulus which describes properties of MR fluid in the pre-yield regime as a function of magnetic field. Data necessary for identification were collected basing on measurements of free vibrations of a three-layered cantilever beam at a special laboratory stand. Magnetic field exerting on MR fluid placed in the beam was generated by electromagnet. In the next step, complex modes of beam vibrations for various places of applying the magnetic field and its strength were calculated.

Abstract: Viscosity test, dynamic shear test, dynamic modulus test and creep test were conducted to investigate the rheological properties of high modulus asphalt and its mixture. Test results indicated that the viscosity of hard grade asphalt could be increased when compared with the ordinary asphalt, especially at high temperatures. The complex shear modulus and dynamic modulus of hard-grade asphalt binder and its mixture were increased, which implied that the stiffness of them was enhanced. Furthermore, the elastically portions for viscoelastic property of asphalt binders were increased, which resulted in the reduction of phase angle for hard grade asphalt binders and mixtures. The rutting parameter for hard-grade asphalt mixture was increased remarkably, which revealed that the resistance to permanent deformation could be significantly improved for hard grade asphalt mixture.

Abstract: The aim of this paper is to investigate the rheological properties of Multi-Walled Carbon NanoTube (MWCNT) enhanced bitumen. The rheological properties of bitumen samples with a range of MWCNT applications are evaluated. The shear complex modulus of the samples increased after ageing, and also increased as the percentage of MWCNTs increased. The viscous component of the complex shear modulus was found to be dominant at higher temperatures, but as the concentration of MWCNTs increased, it was found that the elastic portion started to dominate at higher temperatures. At higher temperatures a change in the phase angle was found, with increased concentrations of MWCNTs causing a decrease in δ, representing a more plastic sample. It is shown that addition of MWCNTs as a modifier did not increase the cracking resistance of the bitumen. Thus, if fatigue cracking is of concern in a certain area it is not recommended to use MWCNTs as a modifier. As the quantity of MWCNTs increased, the temperature at which rutting would start to occur, increased.

Abstract: This study is aimed at evaluating the rate of long-term aging of WMA compared to conventional hot-mix-asphalt (HMA). A test section with recorded traffic and weather information was designated in this study. Field cores of two WMAs and one conventional HMA were taken from the field periodically. Both mix and binder properties of retrieved were measured in the laboratory. The resilient modulus and indirect tensile test were performed to characterize mixture properties. The rheological properties of extracted binder were measured by the dynamic shear rheometer (DSR) in order to obtain the complex shear modulus (G*) as well as the phase angle (δ) of binder with and without the WMA additives.

Abstract: This paper presents a method to simulate the mechanical behavior of magnetorheological fluid (MRF) subjected to magnetic field in the pre-yield region in ANSYS. The main idea is to devide an MRF element into two coincident elements, one of them has density and viscosity without shear modulus while another has shear modulus without density and viscosity. Taking a simply supported MRF sandwich beam as an example, good results and reasonable conclusion are obtained by comparing the results with the theoretical analysis and experimental study of Ref.[1]. The validity of finite element analysis is also investigated in this paper. At present, there is no exactly appropriate element type in ANSYS to model MRF, this kind of method called coincident elements method (CEM) will provide a new way to model the structures with MRF or MR dampers in ANSYS, and it also has reference roles for the future development of related elements in ANSYS.

Abstract: In this study, the stiffening effect of fillers on asphalt binders was characterized through micromechanics and rheology methods. The dynamic shear rheometer (DSR) was used to measure viscoelastic properties of asphalt mastic. Mechanical volume filling effects and additional interacting mechanisms within mastic systems are discussed on the basis of micromechanics-rheology model to predict the complex shear modulus of asphalt mastic from the measured mastic data. It is observed that the phase angle ranges from 88.8o to 89.0o, does not significantly change due to limestone fillers addition. The analytical model prediction of complex shear modulus based on the dynamic shear modulus can be used. Using the nonlinear regression, the Einstein coefficient KE is 4.22, 5.09 and 7.44 for asphalt mixed with limestone, cement and hydrated lime, respectively. Beside, the SEM results explain why the mastic system with hydrated lime shows the highest KE. The behavior of hydrated lime fillers filled mastics is probably due to physico–chemical interaction, which can be validated by further research.

Abstract: The dynamic shear rheometer (DSR) was used to measure viscoelastic properties of asphalt mastic. Mechanical volume filling effects and additional interacting mechanisms within mastic systems are discussed on the basis of micromechanical-rheology model to predict the complex shear modulus of asphalt mastic from the measured mastic data. The Einstein coefficient is 3.761, and the maximum volumetric packing fraction is 0.562 for the measured asphalt mastic. The predicted G* of asphalt mastics is very close to the actual value, and the relative error is not exceeding 10%. The micromechanical-rheology model can predict the complex shear modulus of the asphalt mastic from the viscoelastic property of neat asphalt, the volumetric filler effect and an interactive effect between the filler and the asphalt.