J. Cent. South Univ. (2019) 26: 759-767

DOI: https://doi.org/10.1007/s11771-019-4045-3

Mixing ratio design of emulsified asphalt cold recycled mixture based on gyratory compaction molding

WEI Hui(韦慧)^{1, 2}, BAI Xian-ping(白献萍)^{1, 2}, WANG Fei-yue(王飞跃)³, LI Wei(栗威)⁴, JIN Jiao(金娇)^{1, 2}

1. State Engineering Laboratory of Highway Maintenance Technology, Changsha University ofScience & Technology, Changsha 410114, China;

2. School of Traffic and Transportation Engineering, Changsha University of Science & Technology, Changsha 410114, China;

3. School of Civil Engineering, Central South University, Changsha 410083, China;

4. Henan Transportation Research Institute CO., Ltd, Zhengzhou 450006, China

Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2019

Abstract: In order to study the application of gyratory compaction molding method in emulsified asphalt cold recycled mixture and optimize the relevant technical parameters, the study was carried out according to splitting strength, stability and water stability test; the design of the experiment involved changing gyration number, emulsified asphalt and water content, molded specimen temperature and other factors to analyze the volume parameters, mechanical properties and water stability. The results show that both the maximum dry density and dry and wet splitting strength ratio(DWSSR) of emulsified asphalt cold reclaimed mixture are improved by the rotary compacting method, while the porosity and the optimal dosage of water are reduced. Furthermore, with the increase of compaction times, the porosity and splitting strength index both change exponentially. DWSSR and porosity are consistent with quadratic functions. The use of gyratory compaction for 70 times at 25 °C and the optimum dosage of emulsified asphalt can be determined based on the splitting strength ratio. The high-temperature stability and water damage resistance of the pavement can be improved by the use of rotary compacting method effectively, and the early strength and road performance are higher than the regulatory requirements.

Key words: highway engineering; emulsified asphalt mixture; gyratory compaction; proportion design; splitting strength

Cite this article as: WEI Hui, BAI Xian-ping, WANG Fei-yue, LI Wei, JIN Jiao. Mixing ratio design of emulsified asphalt cold recycled mixture based on gyratory compaction molding [J]. Journal of Central South University, 2019, 26(3): 759–767. DOI: https://doi.org/10.1007/s11771-019-4045-3.

1 Introduction

At present, highway development has gradually entered the key conservation stage, a large number of waste asphalt mixtures are produced by large and medium repair project. Cold in-place recycling technology, which is considered as one of the effective technologies for the disposal of waste materials by the developed countries, allows reduction of waste materials and preservation of natural resources.Because of the particularity of the composition of cold reclaimed mixture, the mix ratio design and the conventional hot mix asphalt mixture are quite different [1]. Most of the current methods are empirical or regional, and the international standard is not formed. Amendments to the Marshall Act, the amendment of the Verme method, the Oregon estimation design method, the Swedish Akzo Nobel design method were proposed by the American Asphalt Regeneration Association (ARRA), and the South African Asphalt Association proposed the “three levels”(level-traffic) design methods [2, 3]. ZHANG et al [4] showed that the second compaction can effectively avoid the volume expansion during the formation of the mixture, but the methods could destroy the cement hydrate crystal structure and affect the strength of the mixture. Marshall crushing method does not precisely simulate the actual stress state of the pavement materials [5, 6], and there is a big difference in the compaction process with the construction site. The theory of mineralization gradation design method with vibration compaction molding also has been proposed [7, 8].

There are few researches on the method of gyratory compaction for emulsified asphalt cold reclaimed mixture. The differences of the mix ratio design for emulsified asphalt cold reclaimed mixture by using the method of gyratory compaction and conventional Marshall are compared. The study is conducted to determine the relevant technical parameters of the gyratory compaction molding method to provide technical guidance for solving the defect problems in the design of the mix ratio of the emulsified asphalt cold recycled mixture.

2 Materials and methods

2.1 Materials

Cationic slow crack emulsified asphalt was used in this study, and the properties are shown in Table 1. The selected reclaimed asphalt pavement (RAP) materials for this study were from the upper layer of a highway milling material, meeting the technical requirements. P.O32.5 Portland cement was selected (Table 2), mixing by drinking water.

2.2 Experimental design

In this Super-pave mix design, the Super-pave gyratory compactor was employed to compact the specimens. The specific design is as follows:

1) Gradation design. Referring to the requirements for medium grain grading, the nominal maximum particle size was 26.5 mm. With the principle of the maximum utilization of old materials, the proportion of new aggregate added is 10%, and cement content is 1%. The gradation design is carried out by external blending method (Table 3).

2) Determination of specimen forming method. Marshall test method was selected for comparison reference. All specimens were compacted to a diameter of 150 mm at a gyratory angle of 1.25° and gyration speed of 30 r/s as specified by strategic highway research program (SHRP) [9].

3) Determination of health preservation method for rotary compaction molding specimen. There is no standard when designing emulsified asphalt mixture for cold regeneration at present. There are different opinions on the temperature, time and sealing state of health preservation.

Table 1 Properties of emulsified asphalt

Table 2 Properties of cement

Table 3 Emulsified asphalt cold regenerated mixture engineering design gradation with different particle sizes

Combined with some representative research results in foreign countries, preservation method for the specimens is proposed. Keep the specimens in the indoor environment for 24 h (25 °C) after being demoded and then heat at 40 °C for at least 72 h. The core samples are taken according to the corresponding test procedure.

4) The effects of factors such as the gyration number, the amount of emulsified asphalt, the temperature of molding specimen and the amount of water are used for mixing on the splitting strength. In order to reduce the variability of test results, 6 specimens were used for each factor index. Key factor parameters are set as follows.

(1) Marshall compaction method cannot reflect the actual stress state of road materials, and its compaction work cannot fully simulate the field crushing work. The super-pave gyratory compactor can simulate the rolling effect of field milling on the mixture, and it is more consistent with the field stress state of the mixture, or closer to the actual engineering situation. The mechanical properties of specimens were analyzed by changing different compaction times. The compaction times are 30, 50, 70 and 100.

(2) The dosages of the emulsified asphalt are 3.0%, 3.5%, 4.0% and 4.5%, respectively. The porosity, splitting strength and other indicators at different dosage are analyzed, and then the optimal amount of asphalt was determined.

(3) Combined with the characteristics of emulsified asphalt mixture, reasonable water content can improve the construction and ease road performance. When the water content of the recycled mixture is small, it is not conducive to the flow and the construction is difficult to compaction. So it is not conducive to cement hydration and affects early strength. If the water content is too large, the effective amount of emulsified asphalt will be reduced. Health maintenance is extended, which does not meet the strength requirement.

(4) In practical engineering, the environmental temperature has a significant influence on the performance of emulsified asphalt mixture. For example, in summer construction, the mixing and compaction effect of the mixture is better; the core taking time is shorter than that of the low temperature environment; and the early strength formation is faster. This paper discusses the effects of the construction temperature on the performance of cold reclaimed asphalt mixture.

3 Results and analysis

3.1 Determination of gyration number

The dosages of the emulsified asphalt are 3.0%, 3.5%, 4.0% and 4.5%, respectively. In addition, the experiment was extended to cover compaction at 30, 50, 70 and 100 times. The study was carried out to discuss the influence on the porosity and fragmentation. The differences of compaction by gyratory compaction and Marshall test comparison are compared.

3.2 Effect of porosity

Figure 1 shows the variation of porosity with the compaction number under different emulsified asphalt dosage. Table 1 summarizes the formula of porosity and compaction number. The analysis shows that: The content of emulsified asphalt and the number of gyratory compaction have a great influence on the porosity. With the increase of the content of emulsified asphalt or the number of gyratory compaction, the porosity will decrease. The relationship between the porosity and compaction number is in accordance with the exponential function (Table 4). The porosity decreases with the increase of compaction number. When compaction number reaches to 70, the change of porosity tends to be gentle. When the content of emulsified asphalt is between 3% and 4%, the porosity is greatly affected by the change of the content of emulsified asphalt, while at 4%–4.5%, the emulsified asphalt content has less influence on the porosity, which indicates that the effect of emulsified asphalt content on porosity has a certain range sensitivity. It is impractical to adjust the emulsified asphalt content for reducing the porosity. This is similar to the effect of compaction number on the porosity.

Figure 1 Influence of asphalt content and compaction number on porosity

Table 4 Relationships between compaction number, porosity, splitting strength under different asphalt content

In summary, both compaction number and emulsified asphalt content have a certain effect on porosity, and the effect will attenuate with the increase of compaction number or emulsified asphalt content.

3.3 Effect of splitting strength

The splitting strength increases with the increase of asphalt dosage and compaction number. At 4.5% asphalt content (100 times of compaction number), the splitting strength reaches a maximum of 0.98 MPa. The splitting strength of the Marshall molded specimen is close to the gyratory compaction one with the compaction number (times) of 30–50. The variation of the splitting strength value of 70 and 100 compaction numbers is shown in Figure 2.

Figure 2 Splitting strength change under different compaction number

For the gyratory compaction number of 70 and 100, the effect of splitting strength decreases first and then increases with the increase of emulsified asphalt content. The improvement effect of specimens at 100 gyratory compaction number is better than that at 70, and with the increase amount of asphalt, the deviations between the two cases improve. When the asphalt content is 4%, the improvement of the two cases is similar with the increase of 14%–16%.

With the increase number of gyratory compaction, the trend of splitting strength is closely related to the amount of emulsified asphalt (Figure 3), and the splitting strength value and gyratory compaction number are in agreement with the quadratic function (Table 4). For the emulsified asphalt content between 4.0%–4.5%, the splitting strengthes of the two are uniformly increased; while between 3.0% and 4.0%, the variability between the splitting strength is large. The results show that the porosity has a good change with the increase of the gyratory compaction number, and splitting strength is the direct reflection of the above results.

Figure 3 Relationship between compaction number and splitting strength

In summary, it is reasonable to be compacted for specimens by 70 times, and the porosity can be controlled at about 10%.

3.4 Determination of mixing water dosage

In the field of mixing process of emulsified asphalt cold recycled mixture, reasonable water content can significantly improve the compaction performance, construction workability and road performance of mixture. The amount of water added in the mixture is usually determined by heavy compaction test. However, due to the large amount of waste materials and the difficulty of controlling the optimal water consumption, the loss of emulsified asphalt or the prolongation of the health time is often caused. Although some related researches also pointed out that there is a big deviation between heavy compaction and field compaction, there is not a good solution yet [10–12]. In this work, the effect of mixing water content on volume parameters is analyzed by means of gyratory compaction and heavy compaction. The results are shown in Figures 4 and 5.

Under gyratory compaction conditions,Figure 4 presents that different molding methods have a significant effect on the dry density and the optimal water content of the specimen. Under gyratory compaction conditions, the maximum dry density value of the specimen is higher than that of heavy compaction, and the corresponding optimum water content is less than that of heavy compaction. For heavy compaction, the maximum dry density and optimum moisture content of the specimen are 2.035 g/cm³ and 3.5%, respectively, while for the rotational compactions those are 2.108 g/cm³ and 2.8%. It can be seen that the gyratory compaction can further improve the compaction density of the specimen and reduce the water consumption by 0.7%.

According to the observation of the field construction process, it is difficult to control the optimal amount of water, and the mixture of water content is too large to blend during the compaction. The use of gyratory compaction method can reduce or avoid this phenomenon. In order to further analyze the effect of water content on other properties, Figure 5 describes DWSSR changes along with the various content of water based on gyratory compaction.

Figure 4 Relationship between water consumption and dry density:

Figure 5 Relationship between water consumption and dry and wet splitting strength ratio

The amount of water has a significant effect, which is in accordance with the quadratic function curve. The DWSSR increases first and then decreases with the increase of water, and the maximum is 0.92 with the best water consumption of 2.8%. It is due to the fact that the durability of the interface determines the performance of the mixture, while the properties of the aggregate and asphalt determine the property of the interface [13]. In the dry state, the failure of the mixture depends on the cohesion of the asphalt, while in the damp state, the performance of the mixture depends on the adhesion between the aggregate and the asphalt [14, 15]. Proper water consumption can improve the binding ability of emulsified asphalt and aggregate, and enhance the interaction between aggregate and emulsified asphalt interface. When the water content of emulsified asphalt is too high, the cohesion of emulsified asphalt will be reduced, and the overall performance of the mixture will be decreased. That is consistent with the maximum dry density analysis, indicating that the ratio of DWSSR is positively related to the dry density of the specimen, and it can be effectively guaranteed only under the optimum water content. Therefore, the method of gyratory compaction is proposed to determine the optimum water content, which can significantly improve the compaction density and reduce the water consumption, and further ensure DWSSR index reliability in this paper.

This paper proposes the use of gyratory compaction method to form emulsified asphalt cold recycled mixture and determine the best water consumption, which can significantly improve the compaction density, reduce water consumption, and further ensure DWSSR.

3.5 Determination of molding temperature

At present, there is a few research on the construction temperature of cold reclaimed mixture with emulsified asphalt. Most of the researches focus on the effect of conservation temperature or temperature on the performance of cold recycled specimen [16]. For example, in the construction under high temperature, the time of coring is shortened, the porosity of pavement is lower and the strength is greater. But this empirical understanding is not conducive to guide the construction and application of emulsified asphalt cold recycled mixture reasonably. The volume parameters and mechanical properties are analyzed under different temperatures, and the results are shown in Figures 6 and 7.

Figure 6 Porosity and bulk density test results under different temperature

Figure 7 Stability and freeze-thaw splitting test results under different temperature

Figure 6 shows that the change of temperature has a direct influence on the volume parameter of emulsified asphalt cold recycled mixture. Along with the increase of temperature, the porosity decreases and the bulk density increases. At 25 and 45 °C (compared with 5 °C), the porosity reduces by 6.1% and 18.3%, while the bulk density increases by about 0.9% and 2.8%. In addition, the porosity and bulk density increase with the molding temperature. On one hand, under the condition of high temperature, the increase of the fluidity of emulsified asphalt binder will enhance the effect of wrapping on the aggregate, and improve the lubricating effect of the emulsified asphalt in the aggregate, which is more favorable for the mixture to compaction and extrusion to improve related properties under the same compaction work [11]. On the other hand, the increase in temperature enhances the interfacial reaction between the emulsified asphalt and the aggregate, thereby enhancing both stiffness and strength of the asphalt binder in the vicinity of the interface [14].

The change of temperature has a great influence on the high temperature stability and water stability. With the increase of temperature, the stability value and DWSSR are also increased. It shows that the performance of emulsified asphalt cold recycled mixture is greatly affected by the construction temperature, and the high temperature performance and water stability can be improved under high construction temperature. For instance, compared to 5 °C, the stability and indirect tensile strength ratio (ITSR) are increased by about 61.8% and 21.3% respectively at 45 °C.

The improvement of high temperature stability in the construction temperature at 5–25 °C is better than those at 25–45 °C, while the ITSR is oppositely. It can be seen that low temperature is unfavorable to the high temperature stability and water damage resistance of the emulsified asphalt cold regenerated mixture, and the fluidity is poor, and poor adhesion to aggregates, the regeneration of the old material is not easy to soften at a lower temperature, that will lead the porosity larger and difficult in control during compaction [17–19]. Therefore, this paper recommends emulsified asphalt cold recycled mixture should be constructed at 25–45 °C, either the demulsification of emulsified asphalt or the construction performance of the mixture can be controlled greatly.

3.6 Determination of emulsified asphalt dosage

According to the above results, the experiment designed that all specimens are compacted for 70 times at 25 °C with 2.8% optimal mixing water content, combined with DWSSR index and porosity index to determine the best amount of emulsified asphalt. The results are presented in Figure 8.

Figure 8 describes the change regulation of the DWSSR and porosity along with different emulsified asphalt dosage. With the increase of emulsified asphalt content, the porosity decreases linearly and the DWSSR changes in a convex curve, which indicates that the emulsified asphalt content can guarantee its excellent performance within a reasonable range. The maximum DWSSR is 92.1%, and the corresponding content of emulsified asphalt is 4.2% and 9.6%, respectively.

In order to further analyze the relationship between DWSSR and porosity under different emulsified asphalt dosage, Figure 9 shows the fitting curve of the two.

Figure 8 Influence of asphalt content of porosity and dry and wet splitting strength ratio:

Figure 9 Relationship between porosity and dry and wet splitting strength ratio

There is a good correlation between DWSSR and porosity, and the two obey the quadratic function with 0.9124 correlation coefficient. The maximum value of DWSSR is 92.3% and the porosity is 9.85%, indicating it can meet the demands under the condition of maximum DWSSR. So it is feasible to determine the optimum amount of emulsified asphalt based on DWSSR [20–23].

Combined with the above research results, the experiment designs that all specimens are compacted for 70 times at 25 °C, with the optimal dosage of water consumption and emulsified asphalt of 2.8% and 4.2%, respectively. The early strength and road performance meet the regulatory requirements after maintenance standard. The results are shown in Table 5. The gyratory compaction molding method can better simulate field construction and control porosity and compaction, and improve road performance of emulsified asphalt mixture.

Table 5 Emulsified asphalt cold recycled mixture performance test results

4 Conclusions

1) The method of gyratory compaction can be effectively applied in the design of mixing ratio for emulsified asphalt cold mix mixture. The parameters and methods for the design of the mixing ratio are proposed, including the gyratory compaction number, the optimal dosage of water consumption and emulsified asphalt, and the molding temperature

2) Porosity or splitting strength and compaction number have a relationship of composite exponential function, while DWSSR and the porosity are consistent with quadratic functions.

3) The gyratory compaction method can effectively increase the maximum dry density and reduce the optimal mixing water consumption. 70 times of gyratory compaction and 25 °C are recommended to determine the optimal mixing water consumption. The DWSSR is used to determine the optimum amount of emulsified asphalt.

4) The early strength and road performance of the emulsified asphalt cold recycled mixture are evaluated by the method of gyratory compaction, and the technical indexes are much higher than the specification, which indicates that the use of gyratory compaction method can improve the stability of high temperature and the ability of water damage resistance significantly.

References

[1] REZVAN B, HASSAN Z. Evaluation of rutting performance of stone matrix asphalt mixtures containing warm mix additives [J]. Journal of Central South University, 2017, 24(2): 360–373.

[2] LI Z G, HAO P W, XU J Z. Study on impacts of freeze-thaw cycles on the shear performances of emulsified asphalt cold recycle mixture [J]. Materials Review, 2016, 30(10): 121–125.

[3] ZHANG J P, ZHU H B, PEI J Z. Evaluation of asphalt emulsification and viscosity of modified asphalt emulsion mortar based on Gompertz model [J]. Journal of Traffic and Transportation Engineering, 2015, 15(5): 1–7.

[4] ZHANG Z Q, YUAN Y J, WANG B G. Information of gyratory compaction densification curve of asphalt mixture and its application [J]. China Journal of Highway and Transport, 2005, 18(3): 182–186. (in Chinese)

[5] SU Z X, LI S M, WU X H. Improvement and performance of cold-recycled mixtures with emulsified asphalt [J]. Journal of East China Jiaotong University, 2014, 31(2): 37–43. (in Chinese)

[6] WANG H, LIU F, ZHANG B Y. Void distribution of emulsified asphalt cold mix with different curing temperature [J]. Journal of Wuhan University of Technology (Transportation Science & Engineering), 2015, 39(2): 388–392. (in Chinese)

[7] WATERS J C, BOSMA G M, HERRINGTON P R. Residual binder extraction from emulsions for quality assurance testing [R]. Wellington: New Zealand Transport Agency, 2008.

[8] WANG De-cai, HAO Pei-wen, LIU Na, ZHANG Hai-wei, LI Zhi-gang. Workability indicator for emulsified asphalt recycled mixture and influence factors [J]. Journal of Beijing University of Technology, 2016, 42(6): 919–925. (in Chinese)

[9] JIA Y, CAO R J, LI B J. Super pave fundamentals reference manual [M]. China Communications Publishing & Media Management Co., Ltd. 2005. (in Chinese)

[10] YAN J H, NI F J, YANG M K. Indirect tensile fatigue properties of asphalt emulsion cold recycled mixes [J]. Journal of Building Materials, 2011, 14(1): 58–61. (in Chinese)

[11] XIONG R, CHEN S F, GUAN B W, TU S, YANG F. Grey correlation entropy analysis of influence factors on the strength of emulsified asphalt mixture [J]. Journal of Zhengzhou University, 2010, 31(6): 60–64. (in Chinese)

[12] DONG M S, GAO Y M, LI L L, WANG L N, SUN Z B. Viscoelastic micromechanical model for dynamic modulus prediction of asphalt concrete with interface effects [J]. Journal of Central South University, 2016, 23(4):926–933.

[13] LI J, ZHANG J H, QIAN G P, ZHENG J L, ZHANG Y Q. Three-dimensional simulation of aggregate and asphalt mixture using parameterized shape and size gradation [J]. Journal of Materials in Civil Engineering, 2019, 31(3): ID 04019004.

[14] GUO M, MOTAMED A, TAN Y Y, BHASIN A. Investigating the interaction between asphalt binder and fresh and simulated RAP aggregate [J]. Materials & Design, 2016, 105: 25–33.

[15] GUO M, TAN Y, ZHOU S W. Multiscale test research on interfacial adhesion property of cold mix asphalt [J]. Construction & Building Materials, 2014, 68(4): 769–776.

[16] ZHOU H S, CAO W D, SUN D Q, LV X X. Effect of water content on emulsion mixture [J]. Journal of Tongji University (Natural Science), 2006, 34(10): 1330–1334. (in Chinese)

[17] WEI T Z, HONG J X, LIN J T. Effect and action mechanism of cement and emulsified asphalt on the strength of cold regeneration [J]. Journal of Building Materials, 2017, 20(2): 310–315. (in Chinese)

[18] LV C B. Influences of Portland RAP on the performance of emulsified asphalt cold regeneration [J]. Journal of Building Materials, 2015, 39(2): 414–418. (in Chinese)

[19] LI Y Y, LI C M, LIU A. Study on molding methods and compressive strength of cement-emulsified asphalt mixture with coupling agent [J]. Journal of Wuhan University of Technology (Transportation Science & Engineering), 2015, 39(6): 126–132. (in Chinese)

[20] OUYANG J, TAN Y Q, LIN Y L, ZHAO J Y. Emulsification process of asphalt emulsion in fresh cement-asphalt emulsion paste [J]. Materials and Structures, 2015, 48(12): 3875–3883.

[21] ZHOU X L, XIE Y J, ZHENG K R, FU Q. Mass change and volume stability of cement emulsified asphalt mortar in wetting-drying cycles [J]. Journal of the Chinese Ceramic Society, 2018, 46(7): 895–904. (in Chinese)

[22] LI Y L, LIU Y Z, JI L, TAN Y Q. Effect of aging on the dynamic mechanical properties of cement emulsified asphalt mastic [J]. Acta Materiae Compositae Sinica, 2018, 35(7): 1975–1982.

[23] QU X, HAO P W. Research the type of mixing molding method on emulsified asphalt mixture [J]. Journal of China & Foreign Highway, 2014, 34(4): 314–317. (in Chinese)

(Edited by FANG Jing-hua)

中文导读

基于旋转压实成型方法的乳化沥青冷再生混合料配合比设计

摘要：为了研究旋转压实成型方法在乳化沥青冷再生混合料中的应用，优化相关技术参数，利用劈裂强度试验、稳定度试验及水稳定性试验，通过改变旋转压实次数、乳化沥青用量、成型试件温度及拌合用水量等因素分析对体积参数、力学性能及水稳定性能的影响。研究结果表明：旋转压实方法能够有效提高乳化沥青冷再生混合料的最大干密度和干湿劈裂强度比指标、降低空隙率及最佳拌合用水量，且随着压实次数的增加，空隙率和劈裂强度指标呈指数函数关系变化。而干湿劈裂强度比指标与空隙率指标则符合二次函数关系。研究推荐采用经旋转压实70次，温度25 °C制备的成型试件，依据干湿劈裂强度比指标确定最佳乳化沥青用量。汇总研究成果，旋转压实成型方法能够有效地在乳化沥青冷再生混合料配合比中应用。利用该方法能够显著提高路面高温稳定性能和抗水损害能力。通过对早期强度和路用性能评价，各项技术指标均高于规范。

关键词：道路工程；乳化沥青混合料；旋转压实；配合比设计；劈裂强度

Foundation item: Projects(51708048, 51704040) supported by the National Natural Science Foundation of China; Project(17C0050) supported by the Scientific Research Project of Hunan Provincial Department of Education for General Scholars, China; Project(kfj160103) supported by the Open Fund of State Engineering Laboratory of Highway Maintenance Technology (Changsha University of Science & Technology), China; Project supported by the Open Fund of Guangxi Key Lab of Road Structure and Materials, China

Received date: 2018-07-13; Accepted date: 2018-11-14

Corresponding author: WEI Hui, PhD, Lecturer; Tel: +86-13574859541; E-mail: wh@csust.edu.cn; ORCID: 0000-0002-2462-8180; WANG Fei-yue, PhD, Associate Professor; Tel: +86-13755104898; E-mail: wfyhn@163.com; ORCID: 0000- 0001-7576-4118