Effect of liquid anti-stripping agents on moisture sensitivity of crumb rubber modified asphalt binders and mixtures

Construction and Building Materials 225 (2019) 112–119

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Effect of liquid anti-stripping agents on moisture sensitivity of crumb rubber modified asphalt binders and mixtures Chongzheng Zhu a, Juncheng Tang a, Henglong Zhang a,b,⇑, Haihui Duan a a Key Laboratory for Green & Advanced Civil Engineering Materials and Application Technology of Hunan Province, College of Civil Engineering, Hunan University, Changsha 410082, China b Hunan Provincial Engineering Research Center for Construction Solid Wastes Recycling, Hunan Yunzhong Recycling Technology Co., Ltd., Changsha 410205, China

h i g h l i g h t s
Influence of liquid ASAs on laboratory performance of CRMA mixture was investigated.
Adding ASAs can improve effectively the adhesion between aggregate and CRMA binder under dry or wet condition.
Compared with M1, T9 and LOF-6500, the CRMA containing LOF-6500 has the highest wet adhesion energy.
Water and high-temperature stability of CRMA mixture are improved obviously by incorporating ASAs.
Negative influence of T9 on low-temperature stability of CRMA mixture is less than that of M1 or LOF-6500.

a r t i c l e

i n f o

Article history: Received 1 April 2019 Received in revised form 15 July 2019 Accepted 18 July 2019

Keywords: Crumb rubber Asphalt mixture Liquid anti-stripping agents Surface free energy Moisture stability

a b s t r a c t Influence of three liquid anti-stripping agents (ASAs) (named as M1, T9 and LOF-6500) with three dosages (0.25%, 0.50%, and 0.75%) on laboratory performance of crumb rubber modified asphalt (CRMA) mixture was investigated. The performance included aggregate–CRMA binder adhesion bond, water stability, high-temperature stability and low-temperature anti-cracking property, which were evaluated by surface free energy (SFE), freeze-thaw indirect tensile strength (ITS), Marshall stability and lowtemperature ITS tests, respectively. The results manifest that the addition of ASAs can improve effectively the adhesion bond between aggregate and CRMA binder under dry or wet condition. Compared with three ASAs, the CRMA containing LOF-6500 has the highest wet adhesion energy. With regard to M1 and LOF-6500, the CRMA incorporating 0.75% dosage shows the highest dry and wet adhesion energy. Additionally, the water resistance and high-temperature stability of CRMA mixture are improved obviously by incorporating ASAs despite of the types and dosages. However, the ASAs can lower the lowtemperature anti-cracking property of CRMA mixture in certain degree, and the influence of T9 is less than that of M1 or LOF-6500. Ó 2019 Elsevier Ltd. All rights reserved.

1. Introduction At present, asphalt pavement has become main type of highway and urban roads. However, with the growth of traffic volume, aggravation of axis and aging effect of thermal and ultraviolet light, virgin asphalt pavement is prone to produce high temperature rutting and low temperature cracking [1,2]. To improve the asphalt pavement performance and prolong the service life of asphalt pavement, adding some modifiers (e.g. crumb rubber and

⇑ Corresponding author at: Key Laboratory for Green & Advanced Civil Engineering Materials and Application Technology of Hunan Province, College of Civil Engineering, Hunan University, Changsha 410082, China. E-mail address: [email protected] (H. Zhang). https://doi.org/10.1016/j.conbuildmat.2019.07.173 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.

styrene-butadiene-styrene copolymer) in virgin asphalt has become the most common method [3–6]. Among these modifiers, crumb rubber (CR) has become a research hotspot and increasingly been used in construction of road pavement. Asphalt modified by CR can not only improve the high-temperature and lowtemperature stability, and the anti-aging property of pavement, but also lower the cost, and contribute to the recycling of waste rubber and environmental protection [7,8]. Current research shows that the water stability of rubber powder modified asphalt (CRMA) mixture prepared by wet process has been improved to a certain extent. However, it is not enough to apply it to permeable pavement and other pavements which require high water stability performance. Besides, the main drawback with crumb rubber modified asphalt (CRMA) made by dry

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process is the lack of cohesion and adhesion, which can lead to the lower moisture resistance and detachment of aggregates [9,10]. Some studies have found that CR added to asphalt mixtures by using dry process or warm mix technology were prone to stripping during actual pavement construction, which resulted in moisture damage of pavement [11–13]. Therefore, it is indispensable to enhance the ability of CRMA mixture to resist moisture. However, at present only a little work has been carried out as follows: Kim et al. [14] and Punith et al. [12] demonstrated that hydrated lime could enhance the water resistance of CRMA mixture; Arabani et al. [11] found that the nanomaterial Zycosoil could improve the ability of CRMA to resist moisture. Thus more research should be conducted to enhance the water stability of CRMA mixture. Many researchers have found that some liquid anti-stripping agents (ASAs) could significantly improve the moisture resistance of virgin asphalt or warm mix asphalt [15–18]. For this reason, it is worthy to conduct a systematic study on the laboratory performance of CRMA mixture with ASAs. The purpose of this work was to investigate influence of liquid ASAs on laboratory performance of CRMA mixture. Three ASAs (named as M1, T9 and LOF-6500) with three dosages (0.25%, 0.50%, and 0.75%) were adopted. The performance, such as aggregate–CRMA binder adhesion bond, water stability, hightemperature stability and low-temperature anti-cracking property, were evaluated by surface free energy (SFE) method, freeze-thaw indirect tensile strength (ITS), Marshall stability and lowtemperature ITS tests, respectively.

Table 3 Essential information of three ASAs. Properties

M1

T9

LOF-6500

Ingredients

Fatty amines derivatives Liquid Amber. (Dark) Amine-like 0.97 10–12 >200 °C >204.4 °C 0.02 g/l

Amidoamines

Amidoamines

Liquid Dark brown Amine-like 0.97 10–12 – – –

Liquid Brown Amine-like 0.97 – – >200 °C –

Physical state Color Odor Specific gravity pH values Boiling point Flashpoint Solubility in water

Table 4 Physical properties of basalt aggregate. Test

Unit

Specification limit

Measured value

Bulk specific gravity Apparent specific gravity LA abrasion loss Sodium sulfate soundness Water absorption Crushing strength

g/cm3 – % % % %

2.50 2.50 30 12 3 28

2.752 2.870 23.1 2.8 0.3 13.0

2.3. Selection of aggregate gradation The gradation of aggregates used in the study is shown in Fig. 1, with 13.2 mm as nominal maximum aggregate size, which is selected according to the requirement of Technical Specifications for Construction of Highway Asphalt Pavements (JTG F40-2004) for AC-13 C (Asphalt Concrete-13 Coarse) [19].

2. Experimental section 2.1. Experimental materials The 60/80 penetration grade virgin asphalt was supplied by SK Corporation, Korea. The physical properties of the virgin asphalt are listed in Table 1. Crumb rubber, 30–40 mesh (0.55–0.28 mm), was provided by Xin-lei Mineral Powder Processing Plant, Hebei Province, China. The fine crumb rubber was obtained by crushing at ambient conditions and its indexes are listed in Table 2. Three types of common liquid ASAs, namely EVOTHERM M1 (M1), T9 and AD-hereÒLOF-6500 (LOF-6500), were adopted in this study. The essential information of ASAs is listed in Table 3. The basalt aggregate was used for producing asphalt mixture in this study and the physical properties of the basalt aggregate are listed in Table 4.

2.2. Preparation of CRMA with ASAs In order to prepare the CRMA incorporating ASAs, the virgin asphalt was firstly heated to molten state at 160 . Subsequently, 12% crumb rubber by weight of virgin asphalt and different dosages (0%, 0.25%, 0.50% and 0.75%) ASAs by weight of virgin asphalt were interfused in virgin asphalt using a mechanical agitator, and the mixture was stirred at a speed of 1500 rpm for 30 min under 177 °C.

Table 1 Physical properties of virgin asphalt.

2.4. Determination of optimum CRMA content in mixture The optimum CRMA content (OCC) in mixture was determined according to JTG F40-T 2004 (China Industry Standard 2004) [19]. Firstly, five contents (3.5%, 4.0%, 4.5%, 5.0% and 5.5%) CRMA by weight of CRMA mixture were selected to make standard Marshall specimens respectively. Then their gross volume relative density (cf), void volume (VV), void in mineral aggregate (VMA), void filled with asphalt (VFA), Marshall stability (MS), and flow value (FL) were measured. The measurement results are shown in Fig. 2. According to the results, the CRMA contents corresponding to the maximum cf, the maximum MS, the median VV and the median VFA can be found on these curves, and take their average as OCC1 (4.6%). The median value of CRMA content range (4.4%–5.2%) which all indexes meet the technical standards is regarded as OCC2 (4.8%). Taking the average values of OCC1 and OCC2 as the optimum CRMA content OCC. Finally, based on the results, the OCC was determined as 4.7%. It is worth adding that the mixing temperature and paving temperature of CRMA mixture are recommended as 170 °C and 155 °C respectively according to Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering (JTG E20-T 0702-2011).

2.5. Test methods

Physical properties

Test results

Penetration (25 °C)/dmm Softening point/ °C Ductility (15 °C)/cm Viscosity (135 °C)/(mPas)

76 48.8 >150 441

Table 2 Indexes of fine crumb rubber. Indexes

Standard value

Test value

Heating loss/% Ash content/% Acetone extract/% Rubber hydrocarbon content/% Carbon black content/%

1.00 8 10 42 26

0.5 7.5 8 48 30

2.5.1. Sessile drop method Surface free energy (SFE) is the increase in free energy when the area of a surface increases by every unit area, which is a physical phenomenon caused by intermolecular interactions at an interface. SFE of CRMA binders in this study was obtained using sessile drop method. Firstly, test asphalt samples were prepared, and the CRMA with ASAs were heated to 160 °C. At the same time, a 2.4  2.4 cm slide was prepared, which was inserted into the heated asphalt and immersed in it for about 30 s. Then, the slide was taken out to hang it naturally, so that the excess asphalt on the surface could fall freely until a uniform and smooth asphalt film was formed on the surface of the asphalt. Put it in an airtight container for 24 h to prevent dust pollution, and then test the contact angle. Drop Shape Analyze 1 was used. The equipment and schematic diagram of test are presented in Fig. 3(a) and (b), respectively. Considering that the probe liquid must not react chemically with or dissolve asphalt binders during the test, three probe liquids (distilled water, glycerol and formamide) were selected. Their SFE components are listed in Table 5. cl represents the SFE of liquid, cdl represents the dispersive component of liquid SFE and cpl represents the polarity or acid-base component of liquid SFE. MATLAB software was used to calculate SFE components of CRMAs.

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Fig. 1. Aggregate gradation curve.

R2  100 R1

2.5.2. Marshall stability test Marshall stability test was performed in accordance to JTG E20-T0709-2011 (China Industry Standard 2011). Firstly, Marshall specimens were compacted by 75 blows on each side with a Marshall hammer, and the specimen size is required to be 101.6 ± 0.2 mm in diameter and 63.5 ± 1.3 mm in height. Subsequently, the samples were conditioned in a 60 °C constant temperature water bath for 30– 40 min. Finally, the specimens were set on the Marshall tester with vertical loading speed of 50 mm/min until reaching the peak value of load. The obtained peak value is the MS value and the corresponding deformation is the FL value, and the Marshall stiffness is the ratio of MS to FL. Three indexes were adopted to assess the high temperature deformation ability of CRMA mixtures.

TSR ¼

2.5.3. Low temperature indirect tensile strength test Low temperature indirect tensile strength (ITS) test was performed in accordance to JTG E20-T 0716–2011 (China Industry Standard 2011). The Marshall specimens were firstly kept at 10 °C condition for 6 h. Then the specimens were set on a material testing machine with vertical loading speed of 1 mm/min until the maximum load was reached. The corresponding failure tensile strain was utilized to assess the low-temperature anti-cracking property of CRMA mixtures in this study, which can be computed as following formulas (1) and (2):

3.1.1. SFE components The contact angle (h) values of three probe liquids on CRMAs are shown in Table 6. As seen in Table 6, with the addition of ASAs, the h of distilled water on CRMA decreases obviously regardless of the types and dosages. The decrease in h indicates that adding ASAs has a positive influence on the ability of water to wet the CRMA surface, namely the hydrophilicity of CRMA is improved. The SFE components of aggregate were obtained according to  the reference [21], as shown in Table 7. The cA , cdA , cpA cþ A and cA represent the SFE, dispersive component, polarity component, acid component and base component of aggregate, separately. Additionally, in order to obtain the SFE components of CRMAs, the formula (4) was adopted [22].The calculated results of SFE components of CRMAs are shown in Table 8. The cC , cdC and cpC represent the SFE, dispersive component and polarity component of  CRMAs separately, and the cþ C and cC represent the acid component  and base component of CRMAs respectively, and the cþ l and cl represent the acid component and base component of probe liquids separately. According to Table 7, the c A of aggregate is far higher than the cþA , illustrating that the aggregate belongs to basic material. Mean2 while, as seen in Table 8, it can be found that the cþ C (6.91 mJ/m ) of 2  the CRMA without ASA is higher than the cC (0.2 mJ/m ), namely this CRMA belongs to acidic material. But, after introducing ASAs into CRMA regardless of the types or dosages, the cþ C deceases sharply while the c C increases rapidly. The CRMAs transform into basic

X T ¼ Y T  ð0:135 þ 0:5lÞ=ð1:794  0:0314lÞ

ð1Þ

eT ¼ X T  ð0:0307 þ 0:0936lÞ=ð1:35 þ 5lÞ

ð2Þ

where XT = level deformation (mm); YT = vertical deformation (mm); m = Poisson ratio, adopted from recommended values; eT = tensile strain. 2.5.4. Freeze-thaw ITS test Freeze-thaw ITS test was performed in accordance to JTG E20-T0729-2011 (China Industry Standard 2011). Firstly, the specimens were compacted by 50 blows on each side with a Marshall hammer, and the specimen size is also required to be 101.6 ± 0.2 mm in diameter and 63.5 ± 1.3 mm in height. Subsequently, the samples were separated into two groups, one for control group and one for experimental group. The latter was immersed in water for 15 min in a vacuum container and the vacuum degree is kept at 97.3–98.7 kPa, and then soaked in water for 30 min at atmospheric pressure. After that, the experimental group was put into a plastic bag containing 10 g of water, the bag was fastened and put in the refrigerator under 18 ± 2 °C for 16 ± 1 h, then take it out and put it in a 60 °C water bath for 24 h. Finally, the experimental group and the control group were placed in 25 °C water for 2 h, and then the ITS test was conducted with the loading speed of 50 mm/min to obtain the maximum load. The tensile strength ratio (TSR) value was utilized to assess the ability of CRMA mixtures to resist water, which can be computed in accordance to the following formula (3):

ð3Þ

where TSR = tensile strength ratio after freeze-thaw damage (%); R2 = ITS of the specimen after freeze-thaw damage at 25 °C (kPa); and R1 = ITS of the specimen before freeze–thaw damage at 25 °C (kPa).

3. Results and discussion 3.1. SFE analysis

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Fig. 2. Marshall test indexes under different CRMA contents.

Fig. 3. Equipment and schematic diagram of test.

Table 5 SFE components (mJ/m2) of three probe liquids. Probe liquids

cl

cdl

cpl

Distilled water Glycerol Formamide

72.8 64.0 58.0

21.8 34.0 39.0

51.0 30.0 19.0

material, which is attributed to the fact that the ASAs are basic materials. As a result, a good bond between a basic binder and a basic aggregate is very difficult to obtain merely by the polarity component [23]. However, it can be observed from Table 8 that the interfusion of ASAs also results in the obvious increase in cdC irrespectively of ASAs types and dosages. Moreover, the cdC of CRMAs (except for the CRMA with 0.75% T9) is apparently higher

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Table 6 Contact angle values (°) of CRMAs. Samples

Distilled water

Glycerol

Formamide

CRMA CRMA+M1-0.25% CRMA+M1-0.50% CRMA+M1-0.75% CRMA+T9-0.25% CRMA+T9-0.50% CRMA+T9-0.75% CRMA+LOF-6500-0.25% CRMA+LOF-6500-0.50% CRMA+LOF-6500-0.75%

108.33 95.75 95.33 97.50 91.75 92.50 83.67 98.17 93.50 97.75

82.00 85.50 85.17 86.50 89.17 88.80 80.17 92.83 79.67 83.83

79.00 80.17 80.83 76.00 84.33 84.17 77.50 86.33 73.50 72.67

Table 7 SFE components (mJ/m2) of aggregate. Aggregate

cdA

cpA

cþA

cA

cA

Basalt

92.03

68.59

7.61

154.55

160.64

Fig. 4. Dry adhesion energy for CRMAs with aggregate.

Table 8 SFE components (mJ/m2) of CRMAs. Samples

cdC

cpC

cþC

cC

cC

CRMA CRMA+M1-0.25% CRMA+M1-0.5% CRMA+M1-0.75% CRMA+T9-0.25% CRMA+T9-0.5% CRMA+T9-0.75% CRMA+LOF-6500-0.25% CRMA+LOF-6500-0.5% CRMA+LOF-6500-0.75%

8.95 15.54 13.03 32.40 14.22 13.63 10.88 17.51 18.89 35.22

2.35 3.76 4.96 0.55 3.63 4.14 10.39 1.09 3.74 0.17

6.91 1.11 1.71 0.05 0.40 0.58 2.27 0.07 1.54 0.01

0.20 3.19 3.59 1.50 8.23 7.40 11.89 4.24 2.27 0.75

11.30 19.30 17.99 32.95 17.85 17.77 21.27 18.60 22.63 35.39

than cpC . It manifests that the main bond between binder and aggregate is provided by the dispersive component [20]. Furthermore, among three ASAs, the CRMA with LOF-6500 shows the most obvious increase in cdC . Compared with different dosages in each ASA, it can be found that the CRMA with 0.75% M1, 0.25% T9 or 0.75% LOF-6500 has the highest cdC .

cl ð1 þ coshÞ=2 ¼

qffiffiffiffiffiffiffiffiffiffi

cdl cdC þ

qffiffiffiffiffiffiffiffiffiffiffi

cl cþC þ

qffiffiffiffiffiffiffiffiffiffi

cþl cC

ð4Þ

3.1.2. Dry adhesion energy The work of adhesion between aggregate and CRMA binder under dry condition is represented by dry adhesion energy

W wet CAW is, the stronger the moisture resistance is. The calculated W wet CAW results for all CRMAs with aggregate in the presence of water are shown in Fig. 5. In this formula, the cCW represents the adhesion between CRMA binder and water, the cAW represents the adhesion between aggregate and water, the cW , cdw and cpW represent the SFE, dispersive component and polarity component of water, respectively. As seen in Fig. 5, with the introduction of ASAs, the W wet CAW augments apparently in contrast to control sample in spite of the types and dosages. The result suggests that ASAs can effectively enhance the adhesion between aggregate and CRMA binder under wet condition. In addition, by comparing three ASAs, the CRMA with LOF-6500 has the most remarkable enhancement. For M1 and LOF-6500, the W wet CAW reaches the biggest value when the dosage is 0.75%, and the increase amplitudes are 84.6% and 90.2% respectively.

W wet CAW ¼ cCW þ cAW  cCA  qffiffiffiffiffiffiffiffiffiffi qffiffiffiffiffiffiffiffiffiffi qffiffiffiffiffiffiffiffiffiffiffi qffiffiffiffiffiffiffiffiffiffiffi qffiffiffiffiffiffiffiffiffiffiffi qffiffiffiffiffiffiffiffiffiffiffi ¼2 cW þ cdC cdA þ cpC cpA  cdC cdw  cpC cpW  cdA cdW  cpA cpW ð6Þ 3.2. Effect of ASAs on freeze-thaw moisture resistance The tensile strength ratio (TSR) results of CRMA mixtures with different ASAs before and after freeze-thaw condition are

dry (W dry CA ), it can be calculated by formula (5) [22]. A higher W CA abso-

lute value means a stronger adhesion. The calculated W dry CA results for all CRMAs with aggregate are presented in Fig. 4. According to Fig. 4, the CRMAs incorporating ASAs show the higher W dry CA than control sample in spite of the types and dosages, manifesting that the adhesion between binder and aggregate is improved. Furthermore, by comparing three dosages for each ASA, the CRMA containing 0.75% M1, 0.75% T9 or 0.75% LOF-6500 has the highest W dry CA , the increase amplitudes are 46.5%, 40.7% and 45.7% respectively.

qffiffiffiffiffiffiffiffiffiffi qffiffiffiffiffiffiffiffiffiffiffi qffiffiffiffiffiffiffiffiffiffiffi W dry cdC cdA þ 2 cþC cA þ 2 cC cþA CA ¼ 2

ð5Þ

3.1.3. Wet adhesion energy The work of adhesion between aggregate and CRMA binder under wet condition is represented by wet adhesion energy (W wet CAW ), it can be calculated by formula (6) [22]. The bigger the

Fig. 5. Wet adhesion energy for CRMAs with aggregate.

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presented in Fig. 6, the higher TSR value means the stronger moisture resistance of CRMA mixture. According to Fig. 6, the TSR values of CRMA mixture after incorporating ASAs are higher than control sample in spite of the types and dosages. It means that all ASAs can improve the ability of CRMA mixture to resist water damage. This result is line with the result from wet adhesion

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energy. But, among different dosages in each ASA, the CRMA mixture with 0.25% M1, 0.50% T9 or 0.25% LOF-6500 has the highest TSR value, and the increase amplitudes are 7.6%, 7.3% and 9.4% of control sample respectively. This optimum dosage results for different ASAs are inconsistent with that from wet adhesion energy. The reason may be that the CRMAs with different ASA types or dosages have different optimum CRMA contents in mixture rather than the single content 4.7%. 3.3. Effect of ASAs on high-temperature stability

Fig. 6. TSR of CRMA mixture with different ASAs.

The Marshall test results of CRMA mixture incorporating different ASAs are displayed in Fig. 7. According to Fig. 7(a), after interfusing ASAs, the change in MS of CRMA mixtures is quite small, except for the CRMA mixture with 0.75% M1 or 0.75% T9. Additionally, as presented in Fig. 7(b) and (c), the interfusion of ASAs decreases the FL value of CRMA mixture while increases the Marshall stiffness obviously, except for 0.25% T9. These results manifest that the high-temperature stability of CRMA mixture is improved effectively by incorporating ASAs. This result is consistent with literature [24]. It may be because that the reaction happened between anhydride in CRMAs and amine in ASAs can produce an organogels which possess exceptional thermal and mechanical stability in contrast to the anhydrides or amine substances [25]. Besides, among all ASAs, the CRMA mixture with 0.50% M1 has the highest Marshall stiffness, the increase amplitude is 77.4% of control sample.

Fig. 7. Marshall test results of CRMA mixture with different ASAs (a) MS, (b) FL value and (c) Marshall stiffness.

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(3) According to Marshall test results, the high-temperature stability of CRMA mixture is improved effectively by adding ASAs. Besides, among all ASAs, the CRMA mixture with 0.50% M1 has the highest Marshall stiffness. (4) Low-temperature ITS test results indicate that the interfusion of ASAs can lower low-temperature crack resistance of CRMA mixture to some extent. Compared with three ASAs, the influence of T9 on low-temperature crack resistance is less than that of M1 or LOF-6500. (5) CRMA mixture with ASAs are suitable for tropical areas where rutting and moisture are the main problems, while it should be limited in cold regions.

Acknowledgement Fig. 8. Failure tensile strain of CRMA mixture with different ASAs.

3.4. Effect of ASAs on low-temperature anti-cracking property The low-temperature ITS test results for CRMA mixture containing different ASAs are shown in Fig. 8. It can be observed that interfusion of various ASAs can lower the failure tensile strain of CRMA mixture, suggesting the worse low-temperature cracking resistance compared with control sample. This result is also accord with literature [24], which is caused by the produced organogels. Moreover, the failure tensile strain of CRMA mixture with T9 is higher than that with M1 or LOF-6500. It suggested that the effect of T9 on low-temperature crack resistance is less than that of M1 or LOF-6500. Besides, among different dosages in each ASA, the CRMA mixture with 0.75% M1, 0.50% T9 or 0.25% LOF-6500 shows the highest failure tensile strain. From all above, it can be determined that the addition of ASAs can improve the high temperature property and moisture resistance of CRMA mixture, while reduce its low temperature crack resistance. Therefore, on one hand, it worth being recommended that these ASAs are used in tropical areas where rutting and moisture are the main problems. On the other hand, the application of theses ASAs in CRMA mixture should be limited in cold regions. 4. Conclusions In this study, the effect of three liquid ASAs with 0.25%-0.75% dosages on the laboratory performance of CRMA mixture was investigated. The following conclusions can be drawn: (1) On the basis of the SFE analysis, after incorporating three liquid ASAs into CRMA, the contact angle with distilled water and acidic component decrease while the basic component and dispersive component increase obviously. Moreover, both dry adhesion energy and wet adhesion energy between CRMA binder and aggregate are enhanced effectively. Compared with three ASAs, the CRMA with LOF-6500 has the highest dispersive component and wet adhesion energy. With regard to M1 and LOF-6500, the CRMA with 0.75% dosage shows the highest dispersive component, dry and wet adhesion energy. (2) Freeze-thaw ITS test results illustrate that the moisture resistance of CRMA mixture is enhanced obviously by incorporating ASAs in spite of the types and dosages. Among three dosages in each ASA, the CRMA mixture with 0.25% M1, 0.50% T9 or 0.25% LOF-6500 shows the highest TSR value.

This work was supported by the Huxiang Youth Talent Program of Hunan Province, the Transportation Science and Technology Development and Innovation Project of Hunan Province (No. 201805), the Science and Technology Planning Project of Changsha (No. kc1703038, kq1706018). The authors gratefully acknowledge their financial support.

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