Fatigue Performance Evaluation of Bitumen with Controlled Stress DSR Test Hong-zhou ZHU 1,*, Er-hu YAN 1 and Zhang-tian LU 2

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1 217 2nd International Conference on Electrical and Electronics: Techniques and Applications (EETA 217 ISBN: Fatigue Performance Evaluation of Bitumen with Controlled Stress DSR Hong-zhou ZHU 1,, Er-hu YAN 1 and Zhang-tian LU 2 1 The Key Laboratory of Road Structure & Material Ministry of Transport, Beijing, PRC 2 Chongqing Jiaotong University, Chongqing, PRC Corresponding author Keywords: Bitumen, Fatigue performance, DSR, Evaluation. Abstract. The forming of pavement structure relies mainly on the bonding aggregate by bitumen cement in bitumen mixture. The bitumen and Bitumen mortar under load are the main body subjected to tensile stress and strain of bitumen pavement, so the fatigue performance of bitumen mixture are directly influenced by the anti- fatigue performance of bitumen. In this paper, based on the time sweep mode of DSR, the fatigue test with controlled stress are carried out on the7#ordinary bitumen and SBS modified bitumen, and the fatigue performance of the two kinds of bitumen is evaluated based on 5% G. Introduction Fatigue cracking is one of the main failure modes of bitumen pavement, and it is also the main consideration factor in the design of bitumen pavement structure. The fatigue resistance of bitumen mixture is an important influence factor to service life of bitumen pavement. In recent years, through the phenomenology methods, extensive research on influence factors to fatigue performance of bitumen mixture are carried out by researchers at home and abroad, exploration on the fatigue mechanism of bitumen mixture from the view of damage has been done, different fatigue models of bitumen mixture has been put forward. The fatigue performance of bitumen has been experimental studied at home and abroad in recent years. With the aid of dynamic shear rheometer, fatigue property of ordinary bitumen is studied by Tan through continuous loading fatigue test under stress mode [1]. Through continuous loading fatigue test under strain mode, the mechanical response law of bitumen mortar under repeated loading is analyzed by Li xiaomin [2]. The effect of temperature on fatigue performance of bitumen is studied by Shenoy A [3].Through the continuous loading fatigue test under the stress and strain mode, the fatigue property of the modified bitumen is studied by Yuan Yan [4]. Two kinds of ordinary bitumen and five kinds of modified bitumen are selected as the research object to discuss the effect of loading mode, loading frequency, test temperature and initial dissipation energy on the fatigue performance of bitumen by K.S. Bonnetti [5]. In this paper, based on the time sweep mode of DSR, the fatigue test with controlled stress are carried out on the7#ordinary bitumen and SBS modified bitumen, and the fatigue equations of different bitumen are obtained. The fatigue performance of the two kinds of bitumen is evaluated based on 5%, and reference can be provided for the design of bitumen mixture. Materials and Methods Materials 7# ordinary bitumen and SBS modified bitumen are the most used in bitumen pavement in our country, so the two kinds of bitumen are used as the research object. According to the rule of "Standard Methods of Bitumen and Bituminous Mixtures for Highway Engineering" (JTG E2-211, the relevant technical indexes have been tested and the test results of technical index of 129

2 7#ordinary bitumen are shown in Table 1, met the quality requirements of petroleum bitumen in heavy traffic; the test results of technical index of SBS modified bitumen are shown in Table 2, in line with the quality of modified bitumen request. Table 1. Technical index of 7#ordinary bitumen. Item Technical requirement result method Penetration (1g 5s 25 C (.1mm 4~6 68 T64 Softening point (ring and ball method ( C T64 Ductility (5cm/min, 5 C (cm 2 28 T65 Flash point ( C 23 T611 Solubility (% 99 T67 Elastic recovery 25 C(% T662 Segregation T661 Kinematic viscosity (135 C (Pa s T625 Table 2. Technical index of sbs modified bitumen. Item Technical requirement result method Penetration(1g 5s 25 C(.1mm 4~6 57 T64 Softening point (ring and ball method ( C 6 67 T64 Ductility (5cm/min, 5 C (cm 2 28 T65 Flash point ( C 23 T611 Solubility (% 99 T67 Elastic recovery 25 C (% T662 Segregation T661 Kinematic viscosity (135 C (Pa s Experimental Principle and Method T625 Figure 1. Schematic diagram of load action of DSR. DSR Principle. Last century, at the end of 8s, Dynamic Shear Rheometer (DSR was introduced from the field of materials to the field of road research to solve the problem that bitumen fatigue test cant be formed by American SHRP program, then research on the fatigue performance of bitumen can be rapidly developed. So far, the research work on the fatigue performance of bitumen is mainly carried out by using the parallel-plate of DSR. In this paper, the bitumen samples is also test with the time sweep of the DSR, and the dynamic shear stress or dynamic shear strain is applied according to the change of the sine law, the load action diagram is shown in Figure 1.Prior to the start of the test, the bitumen sample is placed on the lower parallel plate and the lower parallel 13

3 plate is kept fixed, and the upper parallel-plate is slid up and down to control the distance between the parallel-plates. When the load is applied, the upper parallel plate begins to move from the A point to the B point, and then reverse direction moves to the C point, and finally returns to the A point, so a load cycle ends, and then the next load cycle starts. Under the action of a certain stress or strain, the mechanical behavior of the material is closely related to the temperature of the environment, the time of the load acting on it, and the history of the load action. Under the usual temperature of pavement and traffic load, the bitumen material is realized as a viscoelastic material. When the bitumen is applied on strain of a sinusoidal change, the stress is also a function of the sine wave. Frequency of the two is the same, but the phase of strain lags behind the stress with (< <, as shown in Figure 2, the function of stress can be expressed as: ( sin( t t (1 in the formula, Stress amplification (Pa; Angular frequency, rad/s Phase angle, (t t 2 t Figure 2. Stress-strain relational graph of bitumen. In general, the alternating physical quantities can be simplified calculated by using the plural form to describe, so the alternating stress and strain expressed in the above can be expressed as: i t e (2 i( t e (3 Defined plural shear modulus as: G ( e i (cos sin " G ( ig ( In the formula, G ( the storage modulus, indicates the elasticity of the viscoelastic body, explaining the amount of the stored energy of the linear viscoelastic body (Pa; G " ( the loss modulus, indicates the viscosity of the viscoelastic body, explaining the amount of the loss energy of the linear viscoelastic body (Pa. According to the formula 4, G (. G " ( can be expressed as: G ( cos (5 " G ( sin (6 131 (4

4 The plural modulus of shear modulus G ( is dynamic modulus: 1 2 " 2 G ( G ( 2 G ( G( (7 Similar to the definition of general viscosity, the definition of plural shear viscosity is: ( ( 2 e i " ( i ( i (sin i cos (8 When the bitumen sample is applied with the stress of a sinusoidal variation: t sin( (9 t The strain is also a function of sine wave, but its phase angle lags behind the stress with,that is: sin( t - t (1 In the plural: i t e (11 e (12 i( t- Plural compliance J ( : 1 J ( G i e " J ( ij ( J ( (cos sin ( " 2 J ( J ( 2 J ( J ( (14 Scheme. The times weep mode of DSR is applied, and the parallel plate fixture with the diameter of 8mm is selected, and he test temperature is controlled in 3 C, and the loading frequency is 1Hz(respectively in stress conditions of 5MPa,.1MPa and.15mpa, two kinds of bitumen fatigue test are carried out with controlled stress under repeated loading. Results and Analysis The Criterion of Fatigue Failure The plural shear modulus attenuating to the initial value 5% is one of the most widely used to define the fatigue damage of bitumen [6]. Research shows that under the same stress level and test temperature, good correlation exists between the fatigue life of bitumen determined by 5% and the fatigue life of bitumen mixture determined by 5%, the correlation coefficient reaches.7~.9[7]. So 5% is defined as the criterion of bitumen fatigue failure in this paper. The Failure Process of Different Bitumen In the time sweep test of DSR, under different stress conditions, the change law of plural shear modulus of 7# bitumen and SBS modified bitumen change with loading times show in Figure 3 and Figure 4. From the figure. a Under the action of controlled stress, curve of different aging degree of 7# matrix bitumen and SBS modified bitumen is roughly "S" curve. With the increase of the loading times, a decline occurs in the plural shear modulus of the bitumen, and a turning point exists in the process of decline. Before the turning point, the decline of the complex shear modulus is slow, and 132

5 the decline is rapid after the turning point, until the bitumen test piece was completely destroyed. Therefore, under the stress mode, the curve of bitumen can be roughly divided into the following three stages: initial adaptation stage, semi stable stage and accelerated failure stage. Figure 3. Curve G N OF 7# Ordinary bitumen. Figure 4. CurveG N OF SBS modified bitumen. b With the increasing of stress level, a reduction exists in the initial plural shear modulus of various bitumen and a accelerated attenuation speed occurs in the plural shear modulus, and a obvious reduction exists both in loading times before the test piece destroyed and the loading times corresponding to the plural shear modulus attenuating to 5%. Fatigue Equations of Different Bitumen Related research shows [4, 5], the exponential relationship is obeyed by the fatigue life of bitumen or bitumen mortar obtained in DSR fatigue test and loading strain, and it usually can be expressed by formula 15. N f K In the formula, N f Fatigue life of bitumen; σ Strain applied in the test; K b Regression coefficient, K is related to the shear strength of the material, b indicates the strain sensitivity of bitumen fatigue life. According to the test data, two kinds of the fatigue equation of bitumen with controlled stress can be regressed as follows: 7#ordinary bitumen: b (15 133

6 N (16 SBS modified bitumen: N (17 It can be seen that, in bitumen fatigue test with controlled stress, the sensitivity of fatigue life to stress level of SBS modified bitumen is higher than ordinary bitumen. Main Conclusions In this paper, based on the time sweep mode of DSR, the fatigue tests under constant stress of different types of bitumen are carried out, and the fatigue process stress and fatigue life of the bitumen under constant are analyzed. The main results obtained are as follows: 1 Under the action of controlled stress, the curves of the 7# matrix bitumen and SBS modified bitumen are approximately "S" curve. The fatigue damage of bitumen can be divided into three stages: initial adaptation stage, semi stable stage and accelerated failure stage. 2 With the increasing of stress level, a reduction exists in the initial plural shear modulus of various bitumen and a accelerated attenuation speed occurs in the plural shear modulus, and a obvious reduction exists both in loading times before the test piece destroyed and the loading times corresponding to the plural shear modulus attenuating to 5% 3 In bitumen fatigue test with controlled stress, the sensitivity of fatigue life to stress level of SBS modified bitumen is higher than ordinary bitumen. Acknowledgment Opening Funding Supported by the Key Laboratory of Road Structure & Material Ministry of Transport, Beijing, PRC References [1] Tan Y., Shan L., Li X. Fatigue Characteristic of Bitumen [J]. Geotechnical Special Publication, 28(182: [2] Li Xiaomin. Study on Evaluation Methods and Performance of Bitumen Mortar Based on Rheological Properties [D]. Harbin Institute of Technology, 26. [3] Link R.E., Shenoy A., Link R.E. Fatigue ing and Evaluation of Bitumen Binders Using the Dynamic Shear Rheometer [J]. Journal of ing & Evaluation, 22, 3(4: [4] Yuan Yan. Evaluation of the Fatigue Properties of Modified Bitumen Mortar [D]. South China University of Technology, 25. [5] Bonnetti K., Nam K., Bahia H. Measuring and Defining Fatigue Behavior of Bitumen Binders [J]. Transportation Research Record: Journal of the Transportation Research Board, 22 (181: [6] Liu Quantao. Research on the Fatigue Properties of Bitumen Mortar[D]. Wuhan University of Technology, 28. [7] Wu Shaopeng, Jiang Chenjian, Lin Juntao, etc. Research on Fatigue Characteristic of Aged Bitumen Binder [J]. Journal of Wuhan University of Technology: Transportation Science & Engineering, 213, 37(3: