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Performance evaluation of densemixtures with stabilised rubbermodified asphaltLitao Gengab, Xiaoying Wanga, Ruibo Rena, Faming Chenb & XinlongYangb
a Shandong Provincial Key Laboratory of Road and TrafficEngineering in Colleges and Universities, Shandong JianzhuUniversity, Jinan, People's Republic of Chinab Xinjiang Transportation Planning Surveying and Design Institute,Urumchi, People's Republic of ChinaPublished online: 19 Jun 2014.
To cite this article: Litao Geng, Xiaoying Wang, Ruibo Ren, Faming Chen & Xinlong Yang (2014)Performance evaluation of dense mixtures with stabilised rubber modified asphalt, Road Materialsand Pavement Design, 15:4, 953-965, DOI: 10.1080/14680629.2014.924426
To link to this article: http://dx.doi.org/10.1080/14680629.2014.924426
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Road Materials and Pavement Design, 2014Vol. 15, No. 4, 953–965, http://dx.doi.org/10.1080/14680629.2014.924426
Performance evaluation of dense mixtures with stabilised rubber modifiedasphalt
Litao Genga ,b∗, Xiaoying Wanga, Ruibo Rena, Faming Chenb and Xinlong Yangb
aShandong Provincial Key Laboratory of Road and Traffic Engineering in Colleges and Universities,Shandong Jianzhu University, Jinan, People’s Republic of China; bXinjiang Transportation PlanningSurveying and Design Institute, Urumchi, People’s Republic of China
(Received 7 October 2013; accepted 9 May 2014 )
Asphalt rubber (AR) has been used worldwide in road engineering not only for improvingthe performance of asphalt mixtures but also for providing an advantage in environmentalprotection. Yet the application of AR is greatly restricted in China for its shortcoming ofbeing only possible to be used in a gap or open gradation mixture to ensure stripping resis-tance as well as anti-rutting performance. Stabilised rubber modified asphalt (SRMA) withlower high-temperature viscosity and better store stability than traditional AR was developedin our previous research and has been widely applied in projects with good results. In thispaper, to evaluate the validation of SRMA in dense mixtures, five kinds of dense mixturescommonly used in China were designed with SRMA as binder. Engineering properties, includ-ing high-temperature performance, low-temperature performance, moisture stability, fatigueperformance and mechanical properties, including dynamic modulus and phase angle werelaboratory evaluated and analysed. For the purpose of comparison, a kind of representa-tive styrene-butadiene-styrene (SBS) polymer modified asphalt commonly used in China wasselected to prepare samples with the same gradation of SRMA mixtures, and the same perfor-mance tests were conducted. In addition, a brief cost analysis among SRMA, SBS-modifiedasphalt and traditional AR was performed. Results show good performance and economy ofSRMA and corresponding dense mixtures, thus it is possible, using SRMA for dense mixturedesign in practical engineering, to reduce construction cost.
Keywords: stabilised rubber modified asphalt (SRMA); dense mixture; engineering proper-ties; mechanical properties
1. IntroductionScrap tires have been a serious environmental problem throughout the world as they accumulaterapidly and are not easily disposed of (Fontes, Trichês, Pais, Pereira, & Minhoto, 2009). In order tominimise its impact, crumb rubber from waste tires has been used in asphalt modification resultingin asphalt rubber (AR) binders that have contributed to improving the mechanical properties ofasphalt mixtures (Kaloush, Witczak, & Way, 2002; Peralta et al., 2010; Lo Presti & Airey, 2013;Shatanawi, Biro, Naser, & Amirkhanian, 2013; Way, 2000; Willis et al., 2013). Since the early1970s, the Arizona Department of Transportation has used AR as a modified binder to reducereflective cracking in asphalt mixture rehabilitation overlays (Scofield, 1989; Sousa, Pais, Saim,Way, & Stubstad, 2001). AR has also been used to reduce maintenance and provide a smoothriding surface and good skid resistance. In addition, AR mixtures have been used to reduce noise
∗Corresponding author. Email: [email protected]
© 2014 Taylor & Francis
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in the tire-pavement interface (Zhu & Carlson, 1999). In China, to improve pavement service lifeand to conserve environment, the use of AR in asphalt pavement construction has been a commonpractice in recent years (Bai, Qian, & Cao, 2009; Cao, Ge, Zhou, & Lu, 2006; Wen & Yang, 2008).
However, one of the main defects of AR is that crumb rubber and mastic asphalt are easy tosegregate, which provides a very short time duration for asphalt mixture production and construc-tion after AR is produced. Observations also found that there was stripping in AR mixtures andravelling on the surface after freezing and thawing (Amirkhanian & Arnold, 1993; Doh, Park,Kim, & Kim, 2007b). To ensure enough stripping resistance and anti-rutting performance of ARmixtures, gap (or open) gradation and high asphalt binder content were commonly used for ARmixture design (Geng, Yang, Ren, & Wang, 2013), resulting in high construction cost as com-pared to conventional dense-graded mixture. Regretfully, there is no favourable subsidy for roadcontractors in China, and the further use of AR is largely restricted despite its merits in improvingpavement performance and environmental protection.
On the other hand, much effort has recently been devoted to improving the performance ofthe AR (or crump rubber modified asphalt) mixtures (Doh, Park, Kim, & Kim, 2007a; Putman &Amirkhanian, 2006). A kind of crumb rubber modified asphalt (produced with petroleum asphalt asmastic asphalt, crumb rubber and certain aids) was developed in our former research and has beenapplied in a series of pavement projects in China with good results since 2009 (Ren, 2011). Thiskind of asphalt binder exhibited better store stability than AR. The basic production principle ofthis kind of rubber-modified asphalt is that physical and chemical reactions of desulphurisation,mixing and cross-linking occur in the crumb rubber–asphalt system to obtain a stable colloidsystem under a specific production process. Our former research showed that even over twomonths hot storage, the technical properties of this kind of asphalt binder decayed slightly, andwe named it stabilised rubber modified asphalt (SRMA). In our subsequent study, it was found thatthe high-temperature viscosity of SRMA was appropriately reduced to achieve better workableperformance without losing other performance by process adjustment.
It is well known that the moisture stability of the asphalt mixture is related to its compactiondegree, and the lower the high-temperature viscosity of the binder the higher the compactness ofthe asphalt mixture. As SRMA has lower high-temperature viscosity, and SRMA mixtures areeasier to compact than AR mixtures, designing dense mixtures with SRMA to achieve acceptablemoisture stability as well as to reduce construction cost will be possible.
The purpose of this study was to evaluate the validation of SRMA in dense mixtures (traditionalcontinuous dense-graded mixtures). Technical properties of SRMA were tested in the laboratoryand analysed first. Then two types of dense-graded asphalt mixtures AC-10 (including two kindsof gradations) and AC-13 (including three kinds of gradations) which are commonly used inChina were selected and designed using SRMA as a binder. Engineering properties, includinghigh-temperature stability, low-temperature performance, moisture stability, fatigue performanceand dynamic mechanical property were evaluated by laboratory experiments. During this study,a kind of representative styrene-butadiene-styrene (SBS) polymer modified asphalt commonlyused in China was selected as contrast sample. In addition, a brief cost analysis among SRMA,SBS-modified asphalt and traditional AR was performed. Results show good performance andeconomic advantage of SRMA and corresponding dense mixtures. Thus, it is feasible by usingSRMA for dense mixture design in practical engineering to reduce construction cost.
2. Objective and scope of workThe objective of this study was to identify the validation of SRMA in dense mixture in thelaboratory.
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The scope of work in this research included a laboratory test for technical properties of SRMA inthe penetration grade system and in the performance grade (PG) system, mixture design and eval-uation of engineering and mechanical properties for two types of dense mixtures (total five kindsof gradations) mixed with SRMA. Meanwhile, a kind of representative SBS polymer modifiedasphalt was selected as contrast sample.
3. Technical properties of SRMAIn this paper, SRMA was produced with mastic asphalt of Qilu 70# road petroleum asphalt, crumbrubber and certain aids from a local entrusted asphalt plant in Jinan city, Shandong province. Forreasons of technical privacy protection, the detailed formula and production process of SRMAare not described here.
Considering that SBS-modified asphalt is extensively used in road engineering in China, occu-pying about 80% market share of modified asphalt, a kind of commercial SBS-modified asphaltcommonly used in Shandong province was taken as the compared sample in this research. Tech-nical properties of factory-fresh SRMA, hot-stored for two months SRMA and SBS-modifiedasphalt were tested in the laboratory, and shown in Table 1. The technical performance of arepresentative AR (Wang, Li, & Lu, 2008) is also illustrated in Table 1.
Test results of the technical properties of SRMA and SBS-modified asphalt samples shown inTable 1 indicate that: (1) both SRMA and AR show similar performance rather to that of SBS-modified asphalt, such as the smaller value of ductility and the bigger values of viscosity (135◦Cand 177◦C). (2) It is known that separation index is not a required item for AR because of its poorstorage stability and its production technology on site. But SRMA (fresh or hot-stored for twomonths) shows a rather satisfactory result in terms of separation, which is inferior to SBS-modifiedasphalt but superior to AR. (3) In addition, the high-temperature viscosities (135◦C and 177◦C)of SRMA are significantly lower than those of AR, showing its good workable performance.(4) There was no marked difference in technical properties between hot-stored and factory-freshSRMA samples. (5) the PG of PG 76-28 showed a wide climate applicability of SRMA.
Table 1. Technical properties of SRMA, asphalt rubber and SBS-modified asphalt.
Test results
Factory- Hot-stored SBS-fresh SRMA Asphalt modified
Test items SRMA (two months) rubber asphalt
Penetration (25◦C), 0.1 mm 67 65 63 57.5Ductility (5 cm/min, 5◦C), cm 17 17 11 24Softening point, ◦C 58.9 58.0 60.0 67Flash point, ◦C >300 >300 >300 >300Penetration index 0.094 0.089 0.121 0.170Rotational viscosity (177◦C), Pa·s 0.768 0.755 1.762 0.435Rotational viscosity (135◦C), Pa·s 3.960 3.850 5.221 1.506Elastic restitution (25◦C), % 83 80 68 89Separation, softening point difference (165◦C, 48 h), ◦C 5.7 5.4 – 0.4Gravity (15◦C), g/cm3 1.0445 1.0445 1.0413 1.0283Thin film oven test (163◦C, 5 hr)
Mass loss, % −0.12 −0.15 −0.23 −0.32Penetration ratio (25◦C), % 73.85 75.37 67.42 85.04Ductility (5◦C), cm 9.5 10.0 4.4 16
PG grade 76–28 76–28 – 76–22
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Table 2. PG test results of SRMA (hot-stored for two months) and SBS-modified asphalt.
Test results
Sample category Test item Temperature (◦C) SRMA SBS-modified asphalt
Origin sample G∗/sinδ, kPa 82 1.871 1.58488 1.286 1.047
Rolling thin film oven test sample G∗/sinδ, kPa 76 2.796 2.25582 1.755 1.492
G∗sinδ, kPa 19 – 432216 3945 668013 5730 –
Pav sample Stiffness, MPa −18 189 182−24 356 347
m, MPa/s −18 0.313 0.325−24 0.255 0.268
Table 2 shows the PG test results of SRMA (hot-stored for two months) and SBS-modifiedasphalt. It can be seen that the high temperature PG grade of SRMA is PG 76, which is the samewith that of SBS-modified asphalt. But higher G∗/ sin δ values indicate the better rutting resistanceof SRMA. The smaller values of G∗ sin δ of SRMA show better fatigue performance than that ofSBS-modified asphalt. And the similar S and m values between SRMA and SBS-modified asphaltillustrate their similar low-temperature performance.
4. Marshall mix designThe aggregate used in this study is crushed limestone produced in Jinan city, Shandong provincein China. Physical properties of the aggregate, both coarse aggregate and fine aggregate togetherwith the mineral filler are given in Table 3. Two types of dense mixtures (total five kinds ofgradations) commonly used in Chinese practical projects were selected and the gradations arelisted in Table 4.
In this study, SRMA hot-stored for two months was used for preparing asphalt mixture samples.SRMA binder contents were random chosen according to the experiential binder region of densemixtures. Four Marshall specimens for each gradation were prepared in the laboratory conditionaccording to T0702 in Chinese standard JTG E20-2011. Afterwards, voids in mineral aggregate(VMA) and air voids were evaluated. Table 5 shows the summary of volumetric indexes andbinder content for each gradation.
Table 3. Aggregate properties.
Aggregate type
Test items Coarse aggregate Fine aggregate Mineral filler
Bulk specific gravity, g/cm3 2.693 2.651 –Apparent specific gravity, g/cm3 2.732 2.738 2.690Absorption, % 0.528 1.199 –L.A. Abrasion, % – – 22.36Polishing value, % – – 45
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Table 4. Selected gradations of asphalt mixtures.
Passing per cent of aggregate through standard sieves (mm)
Mixture type 16 13.2 9.5 4.75 2.36 1.18 0.6 0.3 0.15 0.075
AC-10(1) 100 100 94 63 43.5 31.5 23 16 11 8AC-10(2) 100 100 88 51.5 32 22 15 10 7 5AC-13(1) 100 97 81 43.5 25 16 11 7.5 5.5 4AC-13(2) 100 90 69 40 24.5 15.5 11 8 5 4AC-13(3) 100 97 82 51 35 23.5 17 12 8 6
Table 5. Volumetric indexes and binder content of SRMA mixtures.
Mixture type Binder content (%) VMA (%) Volume of air voids (%)
AC-10(1) 5.2 15.2 4.16AC-10(2) 5.2 15.2 4.20AC-13(1) 5.1 14.8 4.07AC-13(2) 5.1 15.6 4.96AC-13(3) 4.7 14.8 4.93
5. Engineering properties of SRMA mixturesLaboratory tests were conducted to estimate the engineering properties of the dense mixturesdesigned above. And for comparison purpose, with the same gradation and binder content, SBS-modified asphalt mixtures were also prepared.
5.1. High-temperature performanceHigh-temperature performances of SRMA mixtures were evaluated by wheel track tests in accor-dance with Chinese standard T0719. Test samples were made with 300 mm length and weight,and 50 mm height by the wheel rolling method in accordance with Chinese standard T0703. Threesamples of each mixture were compacted in this study. The mix was placed in the oven for 5 hoursat the temperature of 60◦C. Then, wheel track tests were carried out under a rubber wheel pressureof 0.7 MPa and a test temperature of 60◦C.
The test results of dynamic stability are shown in Figure 1. These results indicate that thedynamic stability of SRMA mixture was higher than that of SBS-modified asphalt mixture incase of the same gradation and binder content. Figure 1 also indicates the influence of gradationand binder content on dynamic stability of SRMA mixtures.
5.2. Low-temperature performanceBeam bending test was used to evaluate the low-temperature performance of SRMA mixturein accordance with Chinese standard T0715. The mixtures were compacted in accordance withChinese standard T0703, then sawn to the following dimensions: 250 mm long, 30 mm wide and35 mm thick. Six bending beams for each mixture type were prepared in this study. All beamswere cured at −10◦C for over 2 hours before the test. The beam bending test was performed at−10◦C using UTM-100, and the loading speed was set as 50 mm per minute. Flexural tensilestrength and failure strain were computed by the measured peak loading and deflection, shown inFigures 2 and 3, respectively.
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Mixture type
AC-10 (1) AC-10 (2) AC-13 (1) AC-13 (2) AC-13 (3)
Dyn
amic
sta
bilit
y pa
sses
(m
m)
0
1000
2000
3000
4000
5000
6000
SRMA mixturesSBS modified asphalt mixtures
Figure 1. Dynamic stability of mixtures in rutting test.
Mixture type
AC-10 (1) AC-10 (2) AC-13 (1) AC-13 (2) AC-13 (3)
Fle
xura
l ten
sile
str
engt
h (M
Pa)
0
5
10
15
20
SRMA mixturesSBS modified asphalt mixtures
Figure 2. Flexural tensile strength of mixtures in beam bending test.
It can be seen from Figures 2 and 3 that SRMA mixtures had similar flexural tensile strengthand failure strain to those of SBS-modified asphalt mixtures. Thus low-temperature performanceof SRMA mixtures was satisfactory.
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Mixture type
AC-10 (1) AC-10 (2) AC-13 (1) AC-13 (2) AC-13 (3)
Fai
lure
str
ain
(mm
/mm
)
0
500
1000
1500
2000
2500
3000
3500
4000
SRMA mixturesSBS modified asphalt mixtures
Figure 3. Failure strain of mixtures in beam bending test.
5.3. Moisture stabilityMoisture stability of SRMA mixtures is one of the most attractive properties in this study. Freezingand thawing split tests were used in accordance with Chinese standard T0729 to assess moisturestability. For each mixture, eight samples were fabricated by Marshall method and equally dividedinto two groups. One group of specimens were placed in an ambient temperature approximated20–25◦C. While the other group of specimens were frozen at −18◦C for 16 hours after watersaturation then immersed into water of 60◦C for 24 hours. Then the two groups of specimenswere immersed into water of 25◦C for 2 hours. After that, indirect tensile tests were conducted,and an indirect tensile load at a loading speed of 50 mm per minute was used in this study. Tensilestrength ratio (TSR) was calculated by average split strength of specimens undergoing freezingand thawing divided by that of the other group of specimens. Figure 4 presents TSR values of eachmixture. In Chinese specification JTG F40-2004, the severest requirement on TSR of modifiedasphalt mixture is more than 80%, which is depicted in Figure 4 as short dash horizontal lines.These results in Figure 4 show that the TSR values of SRMA mixtures were slightly less thanthose of SBS-modified asphalt mixtures, but all TSR values being greater than 80% indicated thefeasibility of SRMA as binder in dense-graded mixtures.
5.4. Fatigue performanceFour-point beam fatigue tests were carried out with beam fatigue apparatus in accordance withAASHTO T321. Specimens were made by a wheel-rolling molding machine and then cut into380 mm long, 63.5 mm wide and 50 mm thick in size. In this study, the beam fatigue test tem-perature was set as 20◦C, and a repeated haversine load at a frequency of 10 Hz was used. Straincontrol mode was selected in this study, and strain level was set as 800 με for all the specimens.In particular, a fatigue test at a strain level of 600 με and 400 με was conducted on an AC-10(1)type mixture, too. For each strain level, four beams of each mixture were tested.
Table 6 shows the fatigue life of SRMA mixtures and SBS-modified asphalt mixtures at astrain level of 800 με, and Figure 5 shows the linear trend between fatigue life and strain level of
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Mixture typeAC-10 (1) AC-10 (2) AC-13 (1) AC-13 (2) AC-13 (3)
Ten
sile
str
engt
h ra
tio
(%)
0
20
40
60
80
100
120SRMA mixturesSBS modified asphalt maxturesSpecification limit for TSR
Figure 4. TSR results of mixtures.
300 400 500 600 700 800 900Strain level
104
105
106
Fat
igu
e lif
e (t
imes
)
SRMA mixtureSBS modified asphalt mixtureTrend line for SRMA mixtureTrend line for SBS modified asphalt mixture
log(Y) = –0.00243 x + 6.607
R2 = 0.999
R2 = 0.999
log(Y) = –0.00240 x + 6.558
Figure 5. Fatigue life of mixtures versus strain level.
Table 6. Fatigue life of mixtures at strain level of 800 με.
SRMA mixture SBS-modified asphalt mixture
Mixture type Fatigue life Standard deviation Fatigue life Standard deviation
AC-10(1) 46,320 3431 37,550 2592AC-10(2) 45,690 4238 37,210 1588AC-13(1) 43,690 2446 36,580 1281AC-13(2) 41,260 2719 33,240 2996AC-13(3) 28,690 1491 24,260 2172
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Road Materials and Pavement Design 961
AC-10(1) type mixtures. The results indicate the superiority of SRMA mixtures to SBS-modifiedasphalt mixtures in fatigue performance, especially that under real strain level (around 100 με)in pavement structure induced by vehicle load.
6. Mechanical properties of SRMA mixturesThe mechanical property of the asphalt mixture plays an important role in asphalt pavement designsince it relates to pavement distresses such as cracking and rutting. In Mechanistic-empiricalpavement design guide, the dynamic modulus of asphalt mixture is the material property chosenas a key input for asphalt pavement design (Transportation Research Board, 2004). Pavement layerstress, strain and deflection are primary responses calculated using the dynamic modulus, whichis then passed to models with varying degrees of empiricism to provide estimates of cracking andrutting distresses (Gibson, Kutay, Keramat, & Youtcheff, 2009).
As a typical viscoelastic material, the dynamic modulus of the asphalt mixture meets the time–temperature superposition principle. Dynamic modulus master curves can be used to expressthe modulus of the asphalt mixture as a function of temperature and loading rate. In this study,dynamic modulus tests of SRMA mixtures were conducted by Superpave simple performancetester in accordance with NCHRP Project 9-29 Report 614 (Bonaquist, 2008). Test samples werefabricated by Superpave gyratory compactor, then cored and cut into 100 mm in diameter and150 mm in height. Four testing temperatures of 5◦C, 20◦C, 35◦C and 55◦C were chosen and at eachtemperature, the loading frequencies of 10, 5.0, 1.0, 0.5 and 0.1 Hz were selected, respectively.Then dynamic modulus master curves of SRMA mixtures were constructed using the principle oftime–temperature superposition based on the test results. The translational motion of the dynamicmodulus at different temperatures was implemented using nonlinear least square regression, andthe sigmoidal function was used to describe the frequency dependency of the modulus mastercurve (Pellinen & Witczak, 2002).
log∣∣E∗∣∣ = δ + Max − δ
1 + eβ+γ log fr, (1)
where |E∗| is the dynamic modulus of asphalt mixtures, δ is the minimum modulus value, fris reduced frequency, Max is the maximum modulus value and β and γ are shape parameters,respectively.
The relationship between the shift factor α(T ) and the reduced frequency fr is
fr = f · α(T ), (2)
where f is the loading frequency.The shift factor can be calculated by
log [a(T )] = �Ea
19.14714
(1T
− 1Tr
), (3)
where �Ea is the activation energy and Tr is reference temperature.Thus,
log∣∣E∗∣∣ = δ + Max − δ
1 + eβ+γ {log f +(�Ea/19.14714)[(1/T )−(1/Tr)]} . (4)
In Equation (4), Max can be evaluated by the Hirsch mode, thus only four parameters whichare δ, β, γ and �Ea, need to be fitted.
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10–5 10–4 10–3 10–2 10–1 100 101 102 103
Reduced frequency (Hz)
101
102
103
104
105
Dyn
amic
mo
du
lus
(MP
a)
AC-10(1)-SRMAAC-10(2)-SRMAAC-13(1)-SRMAAC-13(2)-SRMAAC-13(3)-SRMA
AC-10(1)-SBSAC-10(2)-SBSAC-13(1)-SBSAC-13(2)-SBSAC-13(3)-SBS
Figure 6. Master curve of dynamic modulus of mixtures.
In this study, the reference temperature was taken as 20◦C. Utilising nonlinear square leastsquare regression according to the testing results of the dynamic modulus at a different temperatureand loading frequency, fitting parameters were decided. Then the shift factors were calculated andthe master curves of the dynamic modulus of all SRMA mixtures were constructed and shownin Figure 6. The regression analysis indicated that a relatively large coefficient of determination(R2 > 0.997, Se/Sy < 0.05) was achieved for all of the mixtures. Clearly, the dynamic modulusof SRMA mixtures was similar to that of SBS-modified asphalt mixtures at high frequency load(homology to low temperature), while it was significantly greater than that of SBS-modifiedasphalt mixture (about 1.5—3 times at 0.1 Hz) at low-frequency load (high temperature).
With the same shift factors, master curves of phase angle were also constructed. Figure 7 showsthe master curves of the phase angle of the AC-10(1) type mixture; the remaining master curvesof phase angle show the same regularity. It was found that the SRMA mixture has a smaller phaseangle than SBS-modified asphalt mixture at low-frequency loading (high temperature).
As shown in Figures 6 and 7, at low-frequency loading (high temperature), the SRMA mixturehas a higher dynamic modulus and smaller phase angle than the SBS-modified asphalt mixture.This may due to the integrative action of the crumb rubber-basic asphalt system in SRMA includingthe high resilience of rubber particles, the deformation resistance provided by the relatively largesize of rubber particles, the relative reduction of the light component in basic asphalt by theabsorption by crumb rubber, the interlocking affection of the rubber particles and so on. Whilethe higher dynamic modulus and the smaller phase angle values represent a greater proportion ofelastic component in the viscoelastic asphalt mixture which would provide better accumulativedeformation (rutting) resistance. Thus, SRMA mixture would contribute to less risk of ruttingdistress in asphalt pavements.
7. Cost analysisA brief comparative analysis of the production cost of SRMA, SBS-modified asphalt as well asAR was performed in this research, shown in Table 7. Thereinto, the modifier loadings were taken
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10–5 10–4 10–3 10–2 10–1 100 101 102 103
Reduced frequency (Hz)
101
102
Ph
ase
ang
le (
deg
ree)
R2= 0.958
R2= 0.962
Figure 7. Master curve of phase angle of mixtures.
Table 7. Cost comparison among SRMA, SBS-modified asphalt and AR.
Cost (RMB/ton)
Modifier Basic Processing FinalBinder type content (%) asphalt Modifier charges production
SRMA 24 5000 4500 200 5103SBS-modified asphalt 4 5000 14000 200 5546AR 24 5000 4500 150 5053
from the conventional content for each kind of modified asphalt in Shandong province, and theunit prices of raw materials were quoted from the average market price in Shandong province in2013. Note that unlike the need for extra equipment investment for AR production, SRMA canbe produced by the same device as that for SBS-modified asphalt production. Therefore, SRMAwould exhibit an economic advantage over traditional AR, let alone SBS-modified asphalt. Inaddition, the above test results show the feasibility of SRMA for traditional dense-graded mixturedesign, when the binder content of the mixture can be significantly reduced.
8. ConclusionsThe following conclusions were reached based on the test and analysis results:
(1) SRMA shows better workable performance and store stability than traditional AR, and thePG of PG 76-28 of SRMA over SBS-modified asphalt shows its wide climate applicability.
(2) Laboratory test and cost analysis results show good performance and economy of SRMAand corresponding dense mixtures, which provides an alternative way in pavementprojects for cutting costs.
(3) SRMA exhibits better rutting resistance over SBS-modified asphalt based upon thecontrastive results of master curves of the dynamic modulus and phase angle.
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FundingThe work presented in this paper was partly sponsored by the Natural Science Foundation of China(51278288) and China postdoctoral science foundation (2013M542412).
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