Road Performance Comprehensive Evaluation of Polymer Modified Emulsified Asphalt Fiber Microsurfacing

To further improve the road performance of microsurfacing, two kinds of polymer modified emulsified asphalt and three kinds of fibers were selected to prepare a variety of microsurfacing mixtures. ,e composition of the microsurfacing was optimized and verified. ,e effects of polymer modified emulsified asphalt and fiber types on the road performance of the microsurfacing were analyzed. Based on TOPSIS method of entropy weight, the road performance of the microsurfacing was comprehensively evaluated, and the microsurfacing with the best comprehensive road performance was optimized. ,e results show that the addition of waterborne polyurethane can further improve the water stability and low-temperature crack resistance of the waterborne epoxy resin modified emulsified asphalt fiber microsurfacing. Adding fiber can effectively improve the road performance of the microsurfacing. After adding polypropylene fiber, the bonding performance and water damage resistance of polymer modified emulsified asphalt microsurfacing were improved to the maximum. After adding basalt fiber, the deformation resistance, the 60°C dynamic stability, and the −10°C splitting strength of polymer modified emulsified asphalt microsurfacing reached the maximum. Among the three fibers, polypropylene fiber microsurfacing has the best comprehensive road performance, followed by basalt fiber microsurfacing.


Introduction
Microsurfacing is to use special mechanical equipment to mix polymer modified emulsified asphalt, coarse and fine aggregates, fillers, water, and additives into slurry mixture according to the design ratio and pave them on the old pavement to form a thin layer. Microsurfacing is a pavement maintenance overlay technology. It has the advantages of low cost, short construction period, and rapid opening of traffic. To meet the higher requirements of pavement maintenance technology under large traffic volume, heavy load, and complex climate conditions, researchers have carried out more research on how to further improve the road performance of microsurfacing, such as water damage resistance, crack resistance, and wear resistance.
At present, many researchers improve the road performance of microsurfacing by optimizing the performance of modified emulsified asphalt binder or adding fiber. Ji et al. [1] determined the optimum asphalt aggregate ratio, emulsifier content, and waterborne epoxy resin (waterborne epoxy resin is a thermosetting material formed by the reaction of epoxy resin emulsion with waterborne epoxy resin curing agent) content at the waterborne epoxy resin modified emulsified asphalt (WEREA, which refers to the thermosetting asphalt composite produced by adding epoxy resin emulsion and waterborne epoxy resin curing agent to emulsified asphalt) microsurfacing by orthogonal test. Li et al. [2] prepared different types of WEREA microsurfacing and studied the shear resistance between the microsurfacing and asphalt pavement under water immersion conditions. Zheng et al. [3,4] prepared waterborne epoxy resin and SBR composite modified emulsified asphalt microsurfacing and explored the durability of the microsurfacing. Liu et al. [5,6] pointed out that adding waterborne epoxy resin can improve the bonding performance, rutting resistance, and water damage resistance of microsurfacing. Chen et al. [7][8][9][10][11] optimized the construction method and open traffic time based on the change of performance of WEREA microsurfacing. Yao et al. [12] prepared discontinuous graded fiber microsurfacing and studied the effects of fiber type and grading type on rutting resistance and crack resistance of the microsurfacing. MS-3 polypropylene fiber microsurfacing has the best crack resistance effect. Sun et al. [13] studied the effects of aggregate gradation, filler type and content, and polypropylene fiber content on the antisliding and wear resistance of the microsurfacing through indoor accelerated loading test. Wang et al. [14] analyzed the effects of different gradation, different aggregate, and fiber type on the water stability and rutting resistance of microsurfacing mixture. Luo et al. [15] analyzed the effects of fiber type and fiber content on microsurfacing crack resistance and rutting resistance and recommended that the optimal fiber content is 0.10-0.20% of the weight of asphalt mixture.
In conclusion, the road performance of microsurfacing such as water damage resistance, crack resistance, and wear resistance can be effectively improved by optimizing the performance of modified emulsified asphalt binder and adding fiber [16,17]. However, there is a lack of systematic and in-depth research on the polymer modified emulsified asphalt fiber microsurfacing. e influence of polymer modifier and fiber type on the road performance of the microsurfacing needs to be further clarified.
e road performance of polymer modified emulsified asphalt fiber microsurfacing can be further improved. At the same time, there are many evaluation indexes for the road performance of microsurfacing, so it is necessary to carry out comprehensive evaluation on its road performance. e purpose of this study is to clarify the influence of polymer modifier and fiber type on the road performance of the microsurfacing and provide a comprehensive evaluation method of microsurfacing, and the polymer modified emulsified asphalt fiber microsurfacing with better comprehensive performance was optimized.

Experimental Plan
To further improve the road performance of microsurfacing, two kinds of polymer modified emulsified asphalt and three kinds of fibers were selected to prepare a variety of microsurfacing mixtures. e composition of the microsurfacing was optimized and verified. e effects of polymer modified emulsified asphalt and fiber type on the bonding performance and deformation resistance of the microsurfacing were analyzed. e water damage resistance, high temperature stability, and low temperature crack resistance of each microsurfacing were tested. e antisliding and wear resistance of polymer modified emulsified asphalt fiber microsurfacing were studied. Based on TOPSIS method of entropy weight, the road performance of the microsurfacing was comprehensively evaluated, and the microsurfacing with the best comprehensive performance was optimized.
is study is of great significance in improving the service quality of microsurfacing, ensuring road driving safety, and prolonging road service life. It provides a certain reference for the scientific evaluation of microsurfacing road performance.

Raw Materials.
Two kinds of polymer modified emulsified asphalt and three kinds of fibers were selected to prepare a variety of microsurfacing mixtures. e raw materials for preparing polymer modified emulsified asphalt include asphalt, emulsifier, and modifier. e 90# asphalt and mixed cationic slow-cracking medium-setting emulsifier were adopted. According to the previous research [9,10], waterborne epoxy resin (it includes epoxy resin emulsion and waterborne epoxy curing agent; their mass ratio is 1 : 1) and waterborne polyurethane were used to prepare polymer modified emulsified asphalt. Polyester fiber (PETF), polypropylene fiber (PPF), basalt fiber (BF), and portland cement (P.O. 32.5) were selected. e microsurfacing was prepared by using polymer modified emulsified asphalt, limestone mineral filler, basalt aggregate, fiber, cement, etc. Referring to the MS-3 grading in Technical Guide for Micro-Surfacing and Slurry Seal, China [18], and in combination with the grading of microsurfacing which was widely studied and applied in China [3][4][5][6][7], the grading of microsurfacing in this study was determined. e lower layer of the composite specimen for microsurfacing performance test adopted the AC-13 grading median specified in Technical Specifications for Construction of Highway Asphalt Pavements (JTG F40-2004), China [19], SBS modified asphalt was selected, and its asphalt aggregate ratio was 5%. e main technical indexes of each material are shown in Tables 1-3. e gradation of microsurfacing and AC-13 asphalt mixture is shown in Table 4.

Preparation of Polymer Modified Emulsified Asphalt.
According to the existing research results [3][4][5][6][7], WEREA with 8% (mass percentage of modifier in modified emulsified asphalt) by mass of waterborne epoxy resin was prepared. To further improve the low-temperature toughness of WEREA, composite modified emulsified asphalt (WERPUEA) with 4% by mass of waterborne epoxy resin and 4% by mass of waterborne polyurethane was prepared. e polymer modified emulsified asphalt was prepared by emulsifying first and then modifying. Emulsified asphalt was prepared by colloidal mill, and the processing fineness can reach 2-4 μm. e content of emulsifier is 0.9% of the mass of emulsified asphalt. During the preparation process, the temperature of asphalt was controlled at 130-135°C and the soap solution was controlled at 50-55°C. A certain mass of emulsified asphalt and modifier were weighed; the modifier was added to emulsified asphalt and mixed evenly. e mixture was mixed by high speed mixing shear apparatus at a low speed (100-300 r/min) for 3 min, and then it was mixed by high speed (500-800 r/min) shear for 2 min. Finally, it was manually stirred slowly for 1 min to defoaming.

Preparation of Microsurfacing
Mixture. Referring to Technical Guide for Micro-Surfacing and Slurry Seal, China [18], and combined with the existing research and application results [3][4][5][6][7], the composition of microsurfacing has been preliminarily determined. e asphalt aggregate ratio of the microsurfacing mixture is 7.0-8.0%. e water consumption is 6-10% of the mass of mineral materials. e cement content is 1.5% of the mass of mineral materials. e fiber content is 0.2% of the mass of the microsurfacing mixture. e microsurfacing preparation scheme is shown in Table 5.

Test Methods.
Based on the performance indexes such as mixing time, cohesion torque, wet track abrasion loss value, and sticky sand value, the composition of the microsurfacing was optimized and verified. e effects of polymer modified emulsified asphalt and fiber types on the bonding performance and deformation resistance of the microsurfacing were analyzed. e water damage resistance, high temperature stability, and low temperature crack resistance of the microsurfacing were tested. e antisliding and wear resistance of the microsurfacing were studied. e test process is shown in Figure 1.

Basic Performance Test Method
(1) Mixing Time. About 100 g of mineral aggregate, mineral filler, fiber, etc. was added to the mixing cup. ey were mixed. Water and modified emulsified asphalt were poured in turn. Mix and start to record the time. When the microsurfacing mixture begins to thicken and the hand feels strong, it indicates that the mixture begins to show signs of demulsification. Record the time at this moment, that is, the mixing time.
(2) Cohesion Torque Test. e cohesion torque tester was used to simulate the influence of the horizontal force generated by the vehicle on the microsurfacing mixture. e where WTAT is wet track abrasion loss value of the microsurfacing; m a is mass of test piece before abrasion, g; m b is mass of test piece after abrasion, g; A s is abrasion area, m 2 .
(4) Load Wheel Test. e test piece with length, width, and height of 380 mm × 50 mm × 12.7 mm was formed. e test piece was rolled 1000 times with the load wheel tester at 25 ± 2°C. After rolling, the specimen was taken out, washed, and dried at 60°C to constant weight. e weight G a of the test piece was weighed. e 300 g hot sand with a temperature of 82°C was poured into the sand frame and flattened. en the load wheel tester was started and rolled for 100 times. e weight G b of the test piece after adhering the sand was weighed. e sticky sand value LWT is calculated according to where LWT is sticky sand value, g/m 2 ; A f is the rolling area, m 2 .

e Bonding Performance and Deformation Resistance Test
(   Polyester fiber (PETF) 3 Polypropylene fiber (PPF) 4 Basalt fiber (BF) 5 WERPUEA Polyester fiber (PETF) 6 Polypropylene fiber (PPF) 7 Basalt fiber (BF) 4 Advances in Materials Science and Engineering 30 cm × 30 cm × 3 cm was selected for the lower layer of the microsurface bonding performance test specimen, and the microsurfacing mixture with the thickness of 1.0-1.2 cm was paved on the upper layer. e quick drying AB adhesive was used to bond the puller to the surface of the cured specimen. Under the condition of 25°C, the pull-off strength was tested with a pull-out tester, and the loading rate was 10 mm/min. e pull-off strength is calculated according to where σ is the pull-off strength, MPa; F is the failure load, N; A is the bonding area of the test specimen, mm 2 .
(2) Stability and Resistance to Compaction Test. e test piece was formed according to the load wheel test. e width L a of the specimen was measured. e test piece was put into the load wheel tester, and it was rolled 1000 times at 22 ± 2°C. After rolling, the specimen was taken out, and the width L b of the specimen after rolling was measured again. e width change rate PLD of the specimen were calculated according to

Antisliding and Wear Resistance Test
(1) Antisliding Performance Test. According to Field Test Methods of Highway Subgrade and Pavement (JTG 3450-2019), China [22], the antisliding performance of the microsurfacing was evaluated by British Pendulum Number.
e British Pendulum Number was tested at three different test points of the specimen. At the same time, considering the temperature correction, the test results were converted into the British Pendulum Number at the standard temperature of 20°C.
(2) Load Wear Test. rough the load wear test of the fourwheel wear tester, the wear mass loss rate was used to evaluate the wear resistance of the microsurfacing. e composite test piece was prepared according to the pull-off strength test method. After paving the microsurfacing, the composite test piece was put into the 60°C oven for curing to constant weight for standby. e load wear test was carried out with the four-wheel wear tester at room temperature. Polyurethane tire (20 cm in diameter and 5 cm in width) with good wear resistance and shore hardness of 70-75 A was selected as the test wheel. e test wheel pressure was 0.7 MPa. e load wear times were 20000 times.

Optimization and Verification of Microsurfacing Mixture
Composition. Taking the microsurfacing prepared by WEREA and PETF as an example, the microsurfacing mixture was prepared by setting three levels of asphalt aggregate ratio of 7%, 7.5%, and 8% and three external water contents of 6%, 8%, and 10%. Based on the performance indexes such as mixing time, cohesion torque, WTAT, and LWT, the composition of the microsurfacing was optimized. Furthermore, the rationality of the composition of other polymer modified emulsified asphalt fiber microsurfacing was verified.

Optimization of Microsurfacing Mixture Composition.
Based on the performance indexes such as mixing time, cohesion torque, WTAT, and LWT, the asphalt aggregate ratio and external water content of WEREA-PETF microsurfacing were optimized. e test results are shown in Figures 2-4.
It can be seen from Figures 2-4 that when the asphalt aggregate ratio is 7-7.5% and the external water content is 6%, the mixing time of the microsurfacing mixture is less than 120 s, which is difficult to meet the mixing requirements of the mixture. Under other conditions, the mixing time meets the relevant requirements in Technical Guide for Micro-Surfacing and Slurry Seal, China [18]. Under the condition of the same asphalt aggregate ratio, the mixing time of the microsurfacing mixture gradually increased with the increase of external water content. Considering that excessive water addition will affect the strength formation of the microsurfacing, the external water content of the microsurfacing was set as 8%, and this external water content was used for subsequent research.

Advances in Materials Science and Engineering
With the increase of asphalt aggregate ratio, the WTAT (immersion for 1 hour) of the microsurfacing gradually decreased, and the LWT and cohesion torque of the microsurfacing gradually increased. When the asphalt aggregate ratio increased from 7% to 7.5%, the WTAT decreased significantly by about 9%. When the asphalt aggregate ratio increased from 7.5% to 8.0%, the WTAT decreased by about 3%, but the LWT increased by 18%. When the asphalt aggregate ratio is 8.0%, slight oil flashing occurred during the rolling process of the load wheel test. erefore, considering the cohesion torque, WTAT, and LWT of the microsurfacing, it is suggested that the asphalt aggregate ratio of the polymer modified emulsified asphalt fiber microsurfacing is 7.5%.

Verification of Microsurfacing Mixture Composition.
Based on the performance indexes such as mixing time, cohesion torque, WTAT, and LWT, the composition of the polymer modified emulsified asphalt fiber microsurfacing was verified. e test results are shown in Figures 5-7.
It can be seen from Figures 5-7 that the mixing time of each polymer modified emulsified asphalt fiber microsurfacing is greater than 120 s and the 30 min cohesion torque and 60 min cohesion torque are greater than 1.2 N·m and 2.0 N·m, respectively, which meets the relevant requirements in Technical Guide for Micro-Surfacing and Slurry Seal, China [18]. At the same time, the WTAT (immersion for 1 hour) and LWTare significantly lower than 540 g/m 2 and 450 g/m 2 specified in Technical Guide for Micro-Surfacing and Slurry Seal, China [18]. e above properties verified the rationality of the external water content and asphalt aggregate ratio of the microsurfacing.
Compared with the microsurfacing without fiber, the mixing time of polymer modified emulsified asphalt fiber microsurfacing was slightly reduced, the cohesion torque was increased 7-16%, the WTAT was reduced by 11-15%, and the LWT was reduced by 10-12%. It shows improved bonding properties and wear resistance.

Road Performance of the Microsurfacing.
e road performance of polymer modified emulsified asphalt fiber microsurfacing, such as deformation resistance, water damage resistance, high temperature stability, low temperature crack resistance, antisliding, and wear resistance, was evaluated. e effects of polymer modifier and fiber type on the road performance of microsurfacing were clarified.

e Bonding Performance and Deformation Resistance.
e bonding performance and deformation resistance of polymer modified emulsified asphalt fiber microsurfacing     were evaluated by pull-off strength and PLD. e results are shown in Figure 8. Figure 8 shows that, compared with the WEREA microsurfacing without fiber, the pull-off strength of the fiber microsurfacing increased by 13-22% and the PLD decreased by 18-32%. e bonding performance and deformation resistance of the microsurfacing are effectively improved. Under the condition of adding the same type of fiber, the bonding performance and deformation resistance of the microsurfacing prepared by WEREA are better than those prepared by WERPUEA. Adding PPF has the greatest improvement on the bonding performance of polymer modified emulsified asphalt microsurfacing. e analysis shows that PPF has the largest oil absorption rate and can play an effective role in reinforcement and bonding in the microsurfacing. e addition of BF can greatly improve the deformation resistance of the microsurfacing. e oil absorption rate of BF is relatively large. At the same time, BF has higher tensile strength and elastic modulus, so that the microsurfacing prepared by BF has improved deformation resistance.

Water Damage Resistance, High Temperature Stability, and Low Temperature Crack Resistance.
e water damage resistance, high temperature stability, and low temperature crack resistance of polymer modified emulsified asphalt fiber microsurfacing were evaluated by the WTAT (immersion for 6 days), DS, the −10°C splitting strength, and tensile strain. e results are shown in Figures 9 and 10.
It can be seen from Figures 9 and 10 that, after adding PETF to the WEREA microsurfacing, the WTAT (immersion for 6 days) increased and the water damage resistance Advances in Materials Science and Engineering decreased slightly. In addition, compared with the WEREA microsurfacing without fiber, after adding other types of fiber, the WTAT (immersion for 6 days) of the microsurfacing reduced by 9-14%, the 60°C dynamic stability increased by 15-29%, the -10°C splitting strength increased by 12-24%, and the -10°C tensile strain increased by 6-13%. e water damage resistance, high temperature stability, and low temperature crack resistance of the microsurfacing have been effectively improved.
Under the condition of adding the same type of fiber, compared with the WEREA fiber microsurfacing, the WTAT (immersion for 6 days) of the WERPUEA fiber microsurfacing reduced by 6-8%, the −10°C splitting strength increased by 4-5%, and the −10°C tensile strain increased by 4-6%. e results show that the addition of waterborne polyurethane can improve the water stability and low-temperature crack resistance of the WEREA microsurfacing.
e addition of PPF has the greatest improvement on the water damage resistance of polymer modified emulsified asphalt microsurfacing, and the addition of BF has the greatest improvement on the 60°C dynamic stability and −10°C splitting strength of the microsurfacing. e −10°C tensile strain of the WERPUEA-PETF microsurfacing reached the maximum. e analysis shows that the high water absorption of PETF leads to the poor water damage resistance of its microsurfacing, but the high elongation at break of PETF increases the low-temperature tensile strain of its microsurfacing.

Antisliding and Wear Resistance.
e antisliding and wear resistance of polymer modified emulsified asphalt fiber microsurfacing were evaluated by British Pendulum Number and wear mass loss rate. e results are shown in Figure 11.
It can be seen from Figure 11 that, after adding fiber, the antisliding performance of polymer modified emulsified asphalt microsurfacing increased slightly, and the British Pendulum Number of each microsurfacing is greater than 70 BPN, which can effectively improve the antisliding performance of the old pavement. After adding fiber to the microsurfacing, the wear mass loss rate after 20000 times of load wear reduced by 8-20%. e wear resistance of the polymer modified emulsified asphalt microsurfacing is effectively improved. e addition of BF has the most obvious effect on the wear resistance of microsurfacing. Under the condition of adding the same type of fiber, the wear resistance of the WEREA microsurfacing is better than that of the WERPUEA microsurfacing.

Road Performance Comprehensive Evaluation of the Microsurfacing.
ere are many road performance evaluation indexes of polymer modified emulsified asphalt fiber microsurfacing, including bonding performance, deformation resistance, water damage resistance, high temperature stability, low temperature crack resistance, antisliding, and wear resistance. Each fiber has different effects on various road performance of the microsurfacing. erefore, it is necessary to carry out the road performance comprehensive evaluation of the microsurfacing and select the fiber microsurfacing with the best comprehensive road performance. e TOPSIS method of entropy weight introduces entropy weight method when determining the weight of evaluation indexes [23,24]. e advantage of this method is that its weight can be determined objectively according to the amount of information provided by each evaluation object index, excluding the influence of human subjective factors. erefore, this method is used to comprehensively evaluate the road performance of polymer modified emulsified asphalt fiber microsurfacing. e sample matrix A � [a ij ] m ×n shown in Table 6 was constructed, including 7 schemes and 8 evaluation indexes. e pull-off strength, dynamic stability, splitting strength, tensile strain, and British Pendulum Number are benefit indexes, and the PLD, WTAT (immersion for 6 days), and wear mass loss rate are cost indexes.
Firstly, Table 6 of the decision matrix was standardized and normalized. e decision matrix A was standardized by using (5) (calculation benefit index) and (6) (calculation cost Next, according to the calculation steps in [23], the entropy weight of each index was calculated as W � Finally, the relative closeness of each scheme (as shown in Table 7) was calculated: C 1 � 0.0312, C 2 � 0.4752, C 3 � 0.7177, C 4 � 0.7110, C 5 � 0.4597, C 6 � 0.6895, C 7 � 0.6610. e relative closeness of each polymer modified emulsified asphalt fiber microsurface treatment scheme is e larger the relative closeness value is, the closer the scheme is to the positive ideal solution; that is, under the comprehensive consideration of the road performance of the microsurfacing, such as bonding performance, deformation resistance, water damage resistance, high temperature stability, low temperature crack resistance, antisliding, and wear resistance, the comprehensive road performance of WEREA-PPF microsurfacing is the best. Among the three fibers, the PPF microsurfacing has the best comprehensive road performance, followed by the BF microsurfacing.
In the actual test process, in general, PPF has the largest comprehensive improvement on the road performance of polymer modified emulsified asphalt microsurfacing, followed by BF. e road performance of PPF microsurfacing is at a high level. e above research results are consistent  with the conclusion drawn by the evaluation system, which shows that the TOPSIS method of entropy weight is applicable to evaluate the comprehensive road performance of the microsurfacing. e addition of fiber can effectively improve the road performance of polymer modified emulsified asphalt microsurfacing. e comprehensive road performance of WEREA-PPF microsurfacing is the best.

Conclusion
(1) Waterborne polyurethane can improve the water stability and low-temperature crack resistance of the WEREA microsurfacing. Compared with the WEREA fiber microsurfacing, the WTAT (immersion for 6 days) of the WERPUEA fiber microsurfacing reduced by 6-8%, the −10°C splitting strength increased by 4-5%, and the −10°C tensile strain increased by 4-6%. (2) After adding fiber, the road performance of the microsurfacing increased by 10-30%. e addition of PPF has the greatest improvement on the bonding performance and water damage resistance of the microsurfacing, and the addition of BF has the greatest improvement on the deformation resistance, the 60°C dynamic stability, and −10°C splitting strength of the microsurfacing. (3) e TOPSIS method of entropy weight is applicable to evaluate the comprehensive road performance of the microsurfacing. e PPF microsurfacing has the best comprehensive road performance, followed by the BF microsurfacing. (4) is study comprehensively evaluated the road performance of polymer modified emulsified asphalt fiber microsurfacing. It is necessary to further clarify the mechanism of fiber strengthening various road performance of microsurfacing.

Data Availability
e data used to support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest
e authors declare that they have no conflicts of interest regarding the publication of this paper.