Repeated Creep Recovery Research Articles

A Creep Model of Steel Slag–Asphalt Mixture Based on Neural Networks

To characterize the complex creep behavior of steel slag–asphalt mixture influenced by both stress and temperature, predictive models employing Back Propagation (BP) and Long Short-Term Memory (LSTM) neural networks are described and compared in this paper. Multiple stress repeated creep recovery tests on AC-13 grade steel slag–asphalt mix samples were conducted at different temperatures. The experimental results were processed into a group of independent creep recovery test results, then divided into training and testing datasets. The K-fold cross-validation was applied to the training datasets to fine-tune the hyperparameters of the neural networks effectively. Compared with the experimental curves, both the effects of BP and LSTM models were investigated, and the broad applicability of the models was proven. The performance of the trained LSTM model was observed by a 95% confidence interval around the fit errors, thereby the creep strain intervals for the testing dataset were obtained. The results suggest that the LSTM model had enhanced prediction compared the BP model for creep deformation trends of steel slag–asphalt mixture at various temperatures. Due to the potent generalization strength of artificial intelligence technology, the LSTM model can be further expanded for forecasting road rutting deformations.

Effect of Fiber Reinforcement on Creep and Recovery Behavior of Cement-Emulsified Asphalt Binder.

In order to evaluate and improve the deformation behavior of cement-emulsified asphalt binder (CA) in cement-emulsified asphalt mixture, this study investigated the reinforcement of small additions of fibers (2%, 4%, and 6% addition by mass of cement) on the deformation resistance of CA. A repeated creep recovery test was implemented that measures the recovery rate of creep deformation and accumulated strain. Further, an improved piecewise curve-fitting method was used to determine the parameters of Burgers model, then the creep compliances were fitted and calculated. The results show the repeated creep recovery test to be a suitable method for obtaining useful information about creep and recovery deformation of fiber-reinforced CA. The influence of fiber types and dosages on the deformation recovery ability is determined based on the creep recovery ratio and accumulated strain. The improved piecewise curve-fitting method has high accuracy. Thereafter, the reinforcement effect was analyzed through the evolution of creep compliance under loading. Therefore, this paper can provide a reference for enhancing the properties of cement-emulsified asphalt mixture by maximizing the fiber reinforcement.

Research on Evaluation Index of High Temperature Performance of Rubberized Asphalt Binder

The high-temperature rheological properties of rubberized asphalt and mixture were evaluated by frequency scanning, repeated creep recovery (RCR) test, temperature sweep test, Hamburg wheel tracking test (HWTT). Based on the Pearson correlation coefficient, the correlation of the mixture gradation and asphalt characteristics with the high-temperature stability of the mixture was analyzed. Finally, the gray correlation theory was applied to analyze the evaluation indexes of the high-temperature rheological properties of rubberized asphalt and mixture. The results show that the asphalt-stone ratio and the fractal dimension (Dc) of coarse aggregate have a significant correlation with the high-temperature performance of the mixture, and the mixture with a smaller asphalt-stone ratio and a higher percentage of coarse aggregate has a better high-temperature performance. The correlation degree of softening point, viscous stiffness modulus and permanent deformation with rubber-asphalt mixture is higher than 0.7, and are significantly higher than those of rotational viscosity at 180°C. Therefore, we recommend the use of permanent deformation, softening point, and viscous stiffness modulus to evaluate the high-temperature performance of rubberized asphalt mixture.

Evaluation of high temperature rheological performance of polyphosphoric acid-SBS and polyphosphoric acid-crumb rubber modified asphalt

This study explores the effects of polyphosphoric acid (PPA) on the rheological performance of styrene butadiene styrene (SBS) and crumb rubber (CR) modified asphalt binders at high temperatures. Four PPA concentrations were selected: 0.4%, 0.8%, 1.2%, and 1.6% by weight of virgin asphalt, and one SBS modified binder with 5% SBS by weight was used as a reference binder. Laboratory tests were performed to simulate short-term and long-term aging. Temperature sweep, frequency sweep, multiple stress creep recovery (MSCR) and repeated creep recovery (RCR) tests were also conducted to investigate the rheological properties of asphalt binders (i.e., PPA-SBS, PPA-CR and SBS modified). Fourier transform infrared spectroscopy (FTIR) test was used to study the chemical reaction of modifiers in the asphalt. Results showed that PPA improved the asphalt’s resistance to permanent deformation and enhanced their elastic recovery behavior. Moreover, results of the rutting factor (G*/sinδ), complex modulus (G*), zero shear viscosity (ZSV), recovery percentage (R), non-recoverable compliance (Jnr) and viscous stiffness modulus (Gv) suggested that PPA-SBS had the best modification effects, followed by PPA-CR. Besides, results of the viscosity-temperature susceptibility (VTS) indicated that the additives decreased the temperature susceptibility of composite modified asphalt binders. PPA modified asphalt binder had good anti-aging behavior when the PPA content was no <0.8% of the virgin asphalt.Additionally, CR-modified asphalt binder with PPA additives exhibited the most improved aging and loading resistance.

APPLICABILITY INDICATORS AND IDENTIFICATION TECHNIQUE FOR A NONLINEAR MAXWELL-TYPE ELASTO-VISCOPLASTIC MODEL USING REPEATED CREEP RECOVERY TESTS

A physically non-linear Maxwell-type constitutive relation for non-aging elasto-viscoplastic materials is considered. General properties of repeated creep recovery curves generated by the relation under four-step uni-axial loadings consisting of two rectangular pulses of stress and two rest periods at zero stress are studied analytically assuming two material functions of the relation are arbitrary. The analysis reveals several characteristic features of the theoretic creep recovery curves and repeated creep recovery curves that can be employed as the relation applicability (or non- applicability) indicators which are convenient for check using test data of a material. Two effective general identification techniques are developed. The first one is based on a set of creep recovery tests at various stress levels and implies measurement of two strain magnitudes in each test. The second one is based on a set of repeated creep and recovery tests and implies measurement of four strain magnitudes in each test. More complex loading program enables to reduce the number of tests and samples twice and to obtain more information on a material behavior and to check a number of additional applicability indicators. The explicit expressions are derived in each case to determine the material functions values at arbitrarily chosen points in stress domain. The identification techniques enable separate and direct evaluation of the material functions values via test data without error accumulation. A number of the identification technique versions are considered and their advantages and shortcomings are discussed. In the case of materials exhibiting creep rate power dependence on stress, a specific rapid procedure is developed for the model identification in the class of power material functions and additional applicability indicators are found. In this case only one repeated creep recovery test and four measured magnitudes of strain are sufficient to determine four material parameters through the explicit expressions obtained.

Application of Infrared Spectroscopy in Prediction of Asphalt Aging Time History and Fatigue Life

Based on attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy and principal component analysis (PCA), four kinds of asphalt (two kinds of matrix asphalts, TPC70# and JL70# and two kinds of modified asphalts, SBS-1 and SBS-2) were aged using the rolling thin-film oven test (RTFOT). The multiple stress repeated creep recovery test (MSCR) was carried out on an AR1500ex dynamic shear rheometer (DSR). The PCA was carried out on the attenuated total reflection infrared spectrum of a pretreated aged asphalt, the principal component factors (oxidation factor and component change factor) were determined, the comprehensive index F was calculated, and a prediction model of aging time history was established and verified. A prediction model for the aging asphalt recovery rate R was established based on the functional group index. The relationship between the recovery rate R and aging time history of each aging asphalt was analyzed and the fatigue life of each aging asphalt based on the rate of dissipated energy change (RDEC) was compared. The correlation between the comprehensive index F and fatigue life of asphalt was also analyzed. The results show that the order of resistance to the high-temperature deformation of each aging asphalt is as follows: SBS-2 &gt; SBS-1 &gt; TPC70# &gt; JL70#; the prediction model of aging asphalt recovery rate R based on functional group index has good reliability. Taking the loading cycle corresponding to the sudden increase of the inflection point of the curve, i.e., the fatigue life NRDEC, as the evaluation index, the fatigue life order of each aging asphalt is SBS-1 &gt; SBS-2 &gt; JL70# &gt; TPC70#. There is a positive correlation between the fatigue life of aged asphalt and the comprehensive index F of asphalt. The correlation degree R2 is 0.85; i.e., with the increase of the comprehensive index F of asphalt, its fatigue life also increases. It was found that it is feasible to analyze the aging time history and fatigue life of asphalt by infrared spectroscopy, and it can provide a rapid and non-destructive prediction method for the practical engineering application of asphalt.

Correlation analysis between aging behavior and rheological indices of asphalt binder

The aging of the asphalt binder seriously affects the performance of the asphalt pavement, so it is expected to obtain indices that can not only evaluate the aging resistance of the asphalt binder but also indicate the performance of the asphalt mixture. In this study, the changing of the rheological indices before and after asphalt aging were observed. The sensitivities to aging characterized by different rheological indices were also compared with each other. Moreover, the relationships among rheological indices were discussed. The results show that the aging has a significant impact on the rheological properties of asphalt. The addition of modifier obviously reduced the low-temperature relaxation modulus of asphalt and increased the absolute value of relaxation rate, thereby improving the low-temperature performance of asphalt road. The sensitivity analysis results of rheological indices to aging behavior show that rheological indice [R3.2kPa] obtained by multiple stress creep recovery test was most sensitive to short-term aging, while rheological indice [R]3.2kPa obtained by repeated creep recovery test was most sensitive to long-term aging, which helps to provide technical support for the quantitative characterization of the aging behavior of asphalt binder. Correlation analysis of rheological indices show that the indice mr(60 s) in frequency sweep test at low temperatures show a linear correlation with the indices Jnr3.2kPa in MSCR test and Nf in linear amplitude sweep test, indicating that the low-temperature relaxation rate of asphalt is closely related to its high temperature performance and fatigue performance.

Investigation on high-temperature performance of waste-based high-viscosity asphalt binders (WHABs) by repeated creep recovery (RCR) test

This study reviewed and compared the test methods for the high-temperature performance of asphalt binder, and selected repeated creep recovery (RCR) test to evaluate the high-temperature performance of three waste-based high-viscosity asphalt binders (WHABs, including D-I, D-II, and F) and a control sample (Tafpack-Super modified asphalt, TMA). Meanwhile, shear stress, test temperature, and aging degree of binders, which could influence high-temperature behavior of binders, were also investigated, and related evaluation indexes including recovery compliance (R), non-recoverable creep compliance (Jnr), and viscous stiffness modulus (Gv) were compared. Results show that WHABs has much better high-temperature performance than TMA; shear stress has the most prominent effect on binders’ high-temperature performance, followed by aging degree, and lastly the selected test temperature in γ–time curve results; R, Jnr, and Gv values results indicate aging degree has a significant effect on binders, and improving binders’ aging performance can greatly improve the high-temperature performance.

Strain accumulation in bituminous binders under repeated creep-recovery loading predicted from small-amplitude oscillatory shear (SAOS) experiments

The creep-recovery (CR) test starts out with a period of shearing at constant stress (creep) and is followed by a period of zero-shear stress where some of the accumulated shear strain gets reversed. Linear viscoelasticity (LVE) allows one to predict the strain response to repeated creep-recovery (RCR) loading from measured small-amplitude oscillatory shear (SAOS) data. Only the relaxation and retardation time spectra of a material need to be known and these can be determined from SAOS data. In an application of the Boltzmann superposition principle (BSP), the strain response to RCR loading can be obtained as a linear superposition of the strain response to many single creep-recovery tests. SAOS and RCR data were collected for several unmodified and modified bituminous binders, and the measured and predicted RCR responses were compared. Generally good agreement was found between the measured and predicted strain accumulation under RCR loading. However, in the case of modified binders, the strain accumulation was slightly overestimated (≤20% relative error) due to the insufficient SAOS information at long relaxation times. Our analysis also demonstrates that the evolution in the strain response under RCR loading, caused by incomplete recovery, can be reasonably well predicted by the presented methodology. It was also shown that the outlined modeling framework can be used, as a first approximation, to estimate the rutting resistance of bituminous binders by predicting the values of the Multiple Stress Creep Recovery (MSCR) test parameters.

Rheology of modified binders under varying doses of WMA additive–Sasobit

ABSTRACTUse of warm mix asphalt (WMA) technology to reduce construction temperatures of asphalt mix has gained strong interest worldwide. However, the technology is still in its inception stage in India. Present study evaluated the rheological properties of polymer- and crumb rubber-modified bitumen with various doses of WMA additive Sasobit (1%, 2%, and 3% by binder weight). Frequency sweep and temperature sweep results showed that increase in Sasobit content improved elastic properties of binders. Creep, repeated creep recovery, and multiple stress creep recovery results showed better resistance toward permanent deformation for Sasobit-modified binders in comparison to control binders.

Investigation on physical and high temperature rheology properties of asphalt binder adding waste oil and polymers

The asphalt binders containing polymer modifier are more and more widespread, which can effectively degrade the disable of asphalt pavement and improve the service life of the road. The waste oil is recycling resource required from natural oil, and it is harmful to the people healthy. The paper researched a new method of the polymer modified asphalt binder containing the waste oil and the relative properties were researched. Experimental results illustrated that the improvement of anti-aging property is noticeable when waste oil and polymer were added into asphalt. The results of dynamic shear rheometer (DSR) showed that the asphalt containing waste oil and polymers has the better high temperature property. Meanwhile, the repeated creep recovery test (RCRT) is employed to simulate the stress and deformation of asphalt binders in pavement. The results also showed that the asphalt binder containing the polymers and waste oil has lower deformation and better recovery. Finally, the storage stability of the asphalt binders is presented. The results proved that the effects of waste oil on storage stability of asphalt/waste oil/polymers blends are little and can be used in pavement after long time storage at high temperature.

Effect of nanoclay on performance of neat and SBS-modified bitumen and HMA

ABSTRACTThe aim of this research was to investigate impact of nanoclay on rutting and moisture damages resistance of neat and SBS-modified asphalt binder and mixture. 4% SBS was blended with 2% nanoclay and 6% nanoclay was used and compared with neat and 4% SBS-modified asphalt binder and mixes. Results of performing rotational viscosity, dynamic shear rheometer, repeated creep recovery, indirect tensile strength, and dynamic creep tests indicated nanoclay has positive impact on rutting and moisture damages resistance of neat and modified asphalt binder.

Creep and recovery behavior characterization of asphalt mixture in compression

A simplified Schapery’s nonlinear viscoelastic model and a modified Schwartz’s viscoplastic model with a proposed stress function are combined to characterize viscoelastic and viscoplastic behaviors of compressed asphalt mixture. In this combined model, the simplified Schapery’s model is used for describing the recoverable strain, and the modified Schwartz’s model is for the irrecoverable strain. The model parameters are determined with the multiple-stress repeated creep–recovery test and the one-hour creep test, and then the combined model is validated with some other tests, including the one-hour creep test at a different stress, the fixed-stress repeated creep–recovery test and the random loading test. Compared with the Perzyna’s viscoplastic model, the modified Schwartz’s model can fit the experimental viscoplastic strain response better in a wide stress range, so that the combined model can predict the creep and recovery behaviors of asphalt mixture under uniaxial compression well.

Three-dimensional microstructural modeling of asphalt concrete using a unified viscoelastic–viscoplastic–viscodamage model

This paper presents a three-dimensional (3D) microstructure-based computational model to predict the thermo-mechanical response of the asphalt concrete using a coupled thermo-viscoelastic, thermo-viscoplastic, and thermo-viscodamage constitutive model. The 3D microstructure of the asphalt concrete is reconstructed from slices of two-dimensional X-ray computed tomography images that consist of the matrix and the aggregate phases and ignoring voids. The matrix is considered as a thermo-viscoelastic, thermo-viscoplastic, and thermo-viscodamage material; while, the aggregates are considered to be linear elastic. The 3D model is subjected to uniaxial compression, tension, and repeated creep recovery tests at different temperatures to investigate the stress–strain behavior, damage propagation, and the patterns of the recoverable and irrecoverable strains. The presented results show that the generated 3D microstructure model along with the presented constitutive model can be used effectively to predict the overall thermo-mechanical response of asphalt concrete. Therefore, the presented framework can be used to provide insight on the influence of the asphalt concrete microstructure on its macroscopic response. In addition, it is a tool to select the mixture components and its proportions to achieve the desired macroscopic properties and performance.

Proposed Refinement of Superpave High-Temperature Specification Parameter for Performance-Graded Binders

A semiempirical approach developed to predict the viscoelastic response of a binder in repeated creep recovery tests is described. This model provides an avenue to predict the rut resistance ( R) as a function of loading (time and load) and temperature from data at a single frequency or frequency sweeps when needed. Thus, it can be used to develop a grading procedure for asphalt binders that not only accurately captures the delayed elasticity of modified binders but also accounts for the effect of traffic speed and traffic loading. The current Superpave binder specification attempts to capture the relative high-temperature performance (i.e., resistance to rut) of a binder via the inverse shear loss compliance, 1/ J” or G*/sin δ, at 10 rad/s. This parameter represents an improvement over the absolute viscosity because it is measured at a defined rate of deformation and accounts to some degree for the viscoelasticity of the binder via the phase angle. The parameter would correctly predict the relative R for an ideally viscous ( R ∞ η) material or an ideally elastic material ( R = ∞). However, there is mounting evidence that at phase angles between 40° and 75°, the parameter may not fully capture the viscoelastic nature of many modified binders. Various authors have shown that the R of mixtures can be well described by models using data from dynamic creep experiments, in which the mix is subjected to a load followed by a relaxation period. More recently, Bahia proposed to capture their high-temperature performance by using a similar technique on neat binders.