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Evaluation of moisture sensitivity of stone matrixasphalt mixtures using polymerised warm mix asphalttechnologiesPunith V. Shivaprasad a , Feipeng Xiao b & Serji N. Amirkhanian ba Asphalt Rubber Technology Service (ARTS), Department of Civil Engineering , ClemsonUniversity , Clemson , SC , 29634 , USAb Guest Professor, Key Laboratory of Silicate Materials Science and Engineering of Ministry ofEducation, Wuhan University of Technology , Wuhan , 430070 , ChinaPublished online: 31 Jan 2012.

To cite this article: Punith V. Shivaprasad , Feipeng Xiao & Serji N. Amirkhanian (2012) Evaluation of moisture sensitivityof stone matrix asphalt mixtures using polymerised warm mix asphalt technologies, International Journal of PavementEngineering, 13:2, 152-165, DOI: 10.1080/10298436.2011.643792

To link to this article: http://dx.doi.org/10.1080/10298436.2011.643792

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Evaluation of moisture sensitivity of stone matrix asphalt mixtures using polymerised warm mixasphalt technologies

Punith V. Shivaprasada*, Feipeng Xiaob1 and Serji N. Amirkhanianb2

aAsphalt Rubber Technology Service (ARTS), Department of Civil Engineering, Clemson University, Clemson, SC 29634, USA;bGuest Professor, Key Laboratory of Silicate Materials Science and Engineering of Ministry of Education, Wuhan University of

Technology, Wuhan 430070, China

(Received 2 March 2010; final version received 21 November 2011)

The present study is focused on using warm mix asphalt (WMA) technology in stone matrix asphalt mixtures andinvestigated in detail on the moisture sensitivity of these mixtures using three different types of WMA technologies.The experimental design involved three sources of aggregates (A, B and C) and three WMA technologies using additivesAsphaminw, Sasobitw and Evothermw technology. Test results indicated that 13 mixtures failed to meet the minimumtensile strength ratio requirement of 85%, and all mixtures tested met the minimum wet indirect tensile strength (ITS) valueof 448 kPa (65 psi) as per SCDOT specifications. Statistical analysis showed that there was significant difference in the wetITS values between aggregate A (micaceous granite) and granite (C) for all the mixtures studied. Statistical analysis showedthat except for two mixtures, there were no significant differences in the wet ITS values of WMA mixtures amongst fourtypes of mixtures under identical conditions. The mixtures containing over 15% rubber (by weight of virgin binder)produced similar resistance to moisture susceptibility compared with mixtures made with PG 76-22 þ fibres.

Keywords: moisture susceptibility; warm mix asphalt; indirect tensile strength; tensile strength ratio; toughness;deformation

1. Introduction

Stone matrix asphalt (SMA) technology has been used in

Europe and the USA for the past 20 years to resist studded-

tire wear and to provide better rutting resistance. On the

basis of US experience, SMAs, which are primarily used as

surface-coarse mixtures, perform better under heavy traffic

loads and are more cost-effective than dense graded

mixtures (Brown and Haddock 1996, Brown et al. 1997,

NAPA 2002, Prowell et al. 2002). This type of rut resistance

mixture has been used by several states in the USA since

1991 and its popularity is growing. SMA is a type of hot mix

asphalt (HMA) consisting of a coarse aggregate skeleton

and a high binder content mortar (Mogawer and Stuart

1994, Stuart and Malmquist 1994, Watson et al. 2004,

2007). The larger coarse aggregate fraction provides rut

resistance through stone-to-stone contact, whereas the

high-binder content (typically 5.5%–7.0% by weight of

mixture) provides durability through an increased film

thickness around the aggregate particles. In order to obtain

high-binder content without excessive draindown, cellulose

fibres with stabilising additives are added to the mixture.

Polymer-modified asphalt binders are typically used in the

production of SMA mixtures due to their rut resistant

properties. The increased viscosities of these binders are

also beneficial to minimise draindown in the mixture

(Brown and Mallick 1995). For the past few years,

increased environmental awareness on global warming and

stricter emission regulations have led to the development of

warm mix asphalt (WMA) to reduce the high mixing

temperatures of regular HMA (Butz et al. 2001, Hurley and

Prowell 2005a, 2005b, 2006, USDOT 2005, Barthel et al.

2007, Wasiuddin et al. 2007, Punith et al. 2011a). Several

demonstration projects were studied in detail using WMA

technologies, and some of the promising advantages

reported are longer paving seasons, longer hauling

distances, reduced wear and tear of the plants, ability to

open the site to traffic sooner, reduced ageing of the binder

in mixtures and thus reduced cracking (Gandhi 2008).

Many researchers believe that lowering temperatures may

not allow for proper drying of aggregates. Especially at the

mixing temperature of 100–1408C, the aggregate may not

be completely dried during the mixing process and the

presence of moisture could prevent binder and aggregate

from adequately bonding, leading to moisture-induced

damage of the mixtures.

Even though some US states and some other countries

have specifications that require a completely dry aggregate

in WMA mixtures (Prowell 2007), there have not been

many research projects conducted in the past to determine

the effects of the moisture susceptibility of SMA mixtures

using WMA additives. There could be resulting moisture

damage which could lead to the failure of the pavement

(Punith et al. 2011b). Based on the popularity of SMA in

the past and the present interest by the state agencies to

ISSN 1029-8436 print/ISSN 1477-268X online

q 2012 Taylor & Francis

http://dx.doi.org/10.1080/10298436.2011.643792

http://www.tandfonline.com

*Corresponding author. Email: pshivap@clemson.edu

International Journal of Pavement Engineering

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adopt WMA technologies, it has become necessary to

better understand the moisture susceptibility of such

mixtures using WMA technologies. This paper presents

the results of the research study using three types of WMA

technologies, (Asphaminw, Sasobitw and Evothermw).

Two types of binders from the same asphalt binder

terminal source, rubber-modified PG 64-22 and polymer-

modified PG 76-22 grade asphalt binder were used in the

present study. The base binder obtained from the supply

terminal was from mixed refinery sources. Cellulose fibres

were used as stabilisers for the SMA mixtures using PG

76-22 binder. The conventional moisture susceptibility

testing procedures such as indirect tensile strength (ITS),

tensile strength ratio (TSR), deformation and toughness

were carried out for the mixtures using WMA additives

and were statistically compared to evaluate the moisture

susceptibility of WMA mixtures.

1.1 Objectives of the present study

The main purposes of the research were to understand the

viability of using WMA technology in SMA and to

compare in detail the moisture-induced damage property

of mixtures using three different types of warm mix

technologies. Specific objectives are as follows:

. to evaluate the moisture susceptibility of rubberised

and polymerised SMA mixtures using WMA

additives;. to evaluate the effect of type of binder, aggregates

and warm mix additive type on the moisture

susceptibility of the SMA mixtures;. to determine the draindown characteristics of SMA

mixtures using WMA technologies and. to evaluate the moisture damage related properties

such as wet toughness, wet ITS and wet deformation

potential of the mixtures using different WMA

technologies.

2. Experimental materials and test procedure

2.1 Materials used in this study

The experimental design adopted in this study included the

use of virgin binder and three WMA additives (Aspha-

minw, Sasobitw and Evothermw), four binder types (PG

64-22 þ 10% crumb rubber (CR), PG 64-22 þ 15% CR,

PG 64-22 þ 20% CR and PG 76-22 þ fibres) and three

aggregate sources (designated as A, B and C). The

engineering properties of coarse and fine aggregate

sources are shown in Table 1. Aggregate B (marble

schist) is a metamorphic rock whereas aggregate sources A

(micaceous granite) and C (granite) are composed

predominantly of quartz and potassium feldspar. Although

both aggregates A and C are granite, the engineering

properties of these two aggregates are very different

(Gandhi 2008). Coarse aggregate A has the highest Los

Angeles (LA) abrasion loss percentage and the highest

absorption, whereas aggregate C has the lowest ones.

A total of 48 types of mixture designs and 192 ITS

specimens were examined in this study. In this study,

hydrated lime was used as an anti-stripping agent for the

mixtures being added into aggregate at 2% by weight of

dry aggregate.

The physical and chemical properties of WMA

additives are presented in Table 2. Asphaminw, Sasobitw

and Evothermw were WMA additives used in this study.

Asphaminw is sodium–aluminium–silicate which is hydro

Table 1. Aggregate gradation, chemical and physical propertiesof aggregates used.

Sieve size Adopted Specified limits

3/400 100 1001/200 93 90 1003/800 73 50 80#4 28 20 35#8 17 16 24#30 15 12 16#50 13 12 15#200 10 8 10

Chemical properties of aggregates used

Aggregate source A B C

Aggregate type Micaceousgranite

Marbleschist

Crushedgranite

Compound Chemical analysis (%)

Al2O3 14.92 7.13 14.28CaO 3.22 19.9 1.49Fe2O3 6.64 5.00 2.32K2O 2.85 2.07 4.25MgO 2.12 12.88 0.33Na2O 2.85 1.15 3.49SiO2 64.44 28.2 72.27TiO2 1.00 0.75 0.29LOI 0.83 21.94 –

Total 98.87 99.02 98.72

Physical properties of aggregates used

LA abrasion loss (%) 43 33 25Absorption (%) 1.1 0.7 0.5Specific gravity for course aggregate

BLK (Dry) 2.69 2.77 2.63BLK (SSD) 2.72 2.78 2.64Apparent 2.77 2.77 2.66

Soundness % loss at 5 cycles3/4 to 3/8 0.1 0.6 1.73/8 to # 4 0.1 0.9 4.1Sand equivalent – 38 53Hardness 5 5 6

Specific gravity for fine aggregateBulk (SSD) 2.59 2.65 2.64Absorption 0.4 0.2 0.6Soundness % loss 4.5 2.8 0.1

International Journal of Pavement Engineering 153

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thermally crystallised as a very fine powder (Table 2). It was

added to the mixture at a rate of 0.3% by weight of the total

mixture. Sasobitw is a long chain aliphatic hydrocarbon

obtained from coal gasification using the Fischer–Tropsch

processw (Table 2). Sasobitw forms a homogeneous

solution with the base binder on stirring (1.5% by weight of

the binder), and produces a marked reduction in the binder

viscosity at 1358C. The mixtures without any WMA

additive were referred to virgin mixture. Evotherm

dispersed asphalt technology is a concentrated solution of

water and chemical additives which is directly injected into

the asphalt line at the mix plant (Table 2).

2.2 Mix design, sample fabrication and testing

The mix design included the aggregates used for a 12.5 mm

mixture that satisfied the specifications set forth by

AASHTO M 325-08 (AASHTO 2008). The design

aggregate gradations for each aggregate source were the

same when using different WMA additives (Virgin binder,

Sasobitw, Asphaminw and Evothermw) and various asphalt

binder types. The rheological properties of asphalt binders

are shown in Table 3. Superpavew mix design defines that

the laboratory mixing and compaction temperatures can be

determined by using a plot of viscosity versus temperature.

There are no previous specifications available regarding the

mixing and compaction temperatures for WMA mixtures;

however, the manufacturer reports a reduction in mixing and

compaction temperatures of 30–508C (Butz et al. 2001,

Barthel et al. 2007), and some researchers have developed

guidelines for mixing and compaction temperatures when

using WMA (Hurley and Prowell 2005b, 2006, USDOT

2005, Barthel et al. 2007). The mixing and compaction

temperatures of materials, as shown in Table 4, were

employed after a series of trial processes.

Table 2. Physical and chemical properties of WMA additives used.

Properties Asphaminw Sasobitw H8 Evothermw H5

Ingredients Sodium aluminosilicate Solid saturated hydrocarbons Fatty acid polyamine condensate waterNa2OzAl2O3z2SiO2

Physical state Granular powder Pastilles, flakes Viscous liquidColour White Off-white to pale brown Amber (dark)Odour Odorless Practically odorless Fishy, amine-likeMolecular weight 365 Approx. 1000 g/moleSpecific gravity 2 (208C) 0.9 (258C) 1.03–1.08Vapor density – – ,1Bulk density 500–600 kg/m3 – 1.03 g/cm3

PH values 11–12 Neutral 9–11Boiling point – – .1008CFlashpoint – 2858C (ASTM D92) –Solubility in water Insoluble Insoluble Water solubility

Table 3. Binder test properties.

Unaged RTFO PAV

Binder types

Viscosityat 1358C

(cP)

G*/sin d(kPa) at

648C

G*/sin d(kPa) at

768C

G*/sin d(kPa) at

648C

G*/sin d(kPa) at

768C

G*sin d(kPa) at

258C

Stiffness(MPa) at2128C

m-valuesat 2128C

PG 64-22 430 1.28 – 2.81 – 4074 217 0.307PG 64-22 þ 10% CR 1270 2.97 – 9.31 2.06 2256 138 0.301PG 64-22 þ 15% CR 2260 – 3.81 6.85 2.99 1361 124 0.315PG 64-22 þ 20% CR 6030 – 3.78 3.17 – 931 82 0.334PG 76-22 1475 – 1.56 – 3.34 3784 219 0.298

Table 4. Mixing and compaction temperatures of WMAmixtures.

Mixture type

10% CRM 15% CRM 20% CRM 3% SBS

Mixing temperature (8F)Virgin 315–325 320–325 325–335 325–335Sasobit 250–265 270–275 290–305 290–305Asphamin 265–275 270–275 290–305 290–305Evotherm 265–275 275–280 290–305 290–305Compaction temperature (8F)Virgin 290–300 300–305 305–310 305–310Sasobit 245–250 255–260 275–285 275–285Asphamin 245–250 255–260 275–285 275–285Evotherm 245–250 260–265 275–285 275–285

P.V. Shivaprasad et al.154

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For this study, the optimum binder content (OBC) was

defined as the amount of binder required to achieve 4.0%

air voids in accordance with AASHTO M 325-08

volumetric specifications (AASHTO 2008). After the

mix designs were completed, for each aggregate/binder

types/warm asphalt additive combination Superpave

gyratory compacted specimens, 150 mm in diameter and

95 mm in height, were prepared with 7 ^ 1% air voids and

then the samples were tested at 258C to determine the ITS,

flow and toughness values. One set of the samples was

tested in dry condition and the other set in wet condition.

The wet samples were conditioned in accordance with

AASHTO T 283. The evaluated parameters included ITS,

TSR, toughness, percentage of flow and toughness loss.

From these tests, the following parameters were obtained

and evaluated:

. ITS and TSR

. Toughness: defined as the area under the indirect

tensile stress–deformation curve up to a defor-

mation of twice that incurred at maximum tensile

stress (Xiao and Amirkhanian 2008).. Percentage of toughness loss (PTL):

PTL ¼Toughness ðdryÞ2 Toughness ðwetÞ

Toughness ðdryÞ

£ 100: ð1Þ

3. Analysis of test results and discussions

Test results of the ITS, toughness and deformation values

were statistically analysed as reported in Tables 6 and 7 at

the 5% level of significance (0.05 probability of a Type I

error) with respect to the effects of aggregate sources,

binder types and WMA additive types. For these

comparisons, it should be noted that all specimens were

produced at OBC. The error bars on the graphs indicate

standard deviation.

3.1 OBC analysis

Table 5 shows the OBC for mix designs with various

percentages of CR content using PG 64-22 grade binder,

with different WMA additives, and with PG 76-22 binder

with fibres. The unit weight of aggregate B material was

found to be higher than the other two aggregate source

types. The lowest maximum specific gravity values were

observed for the loose asphalt mixtures using aggregate C.

All the designed mixtures met the minimum voids in

mineral aggregate (VMA) requirement of 17% as per the

AASHTO specifications (AASHTO 2008). The OBC

values for mixtures with aggregate C were found to be

higher than for mixtures with aggregates A and B. Since

aggregate B has a high-specific gravity for coarse

aggregate (2.77), the OBC values for the majority of Tab

le5

.M

ixtu

red

esig

nan

dd

rain

do

wn

test

resu

lts.

Ag

gre

gat

eA

Ag

gre

gat

eB

Ag

gre

gat

eC

Bin

der

typ

eW

MA

typ

eM

SG

OB

C(%

)V

MA

(%)

VF

A(%

)D

rain

do

wn

(%)

MS

GO

BC

(%)

VM

A(%

)V

FA

(%)

MS

GO

BC

(%)

VM

A(%

)V

FA

(%)

PG

64

-22þ

10

%C

RV

irg

in2

.47

76

.15

18

.57

70

.05

12

.52

75

.70

17

.18

02

.39

66

.70

18

.78

0S

aso

bit

2.4

64

5.7

51

7.3

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0.0

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2.5

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5.7

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7.1

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2.3

88

6.5

51

8.5

79

Asp

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in2

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RV

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.46

26

.05

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32

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36

.00

18

.47

82

.38

27

.35

19

.67

9S

aso

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2.4

73

6.0

51

8.0

77

0.0

40

2.5

11

5.9

01

7.8

78

2.3

85

7.0

01

9.3

80

Asp

ham

in2

.47

06

.40

18

.97

80

.04

72

.53

85

.85

18

.07

72

.38

97

.10

19

.68

0E

vo

ther

m2

.46

36

.40

19

.07

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.00

42

.50

15

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17

.97

92

.38

96

.90

18

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20

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RV

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.46

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20

.01

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66

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19

.88

1S

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0.0

16

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18

.48

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47

.20

19

.78

1A

sph

amin

2.4

64

6.3

51

8.5

78

0.0

51

2.5

08

6.6

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9.3

78

2.3

72

7.0

01

9.6

80

Ev

oth

erm

2.4

58

6.8

21

9.5

79

0.0

16

2.5

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6.3

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8.4

80

2.3

70

7.0

01

9.5

80

PG

76

-22þ

fib

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Vir

gin

2.4

48

6.4

01

8.5

78

0.0

24

2.5

22

5.5

01

7.0

82

2.3

70

7.0

01

9.4

78

Sas

ob

it2

.43

86

.10

17

.77

90

.02

82

.50

15

.85

17

.38

12

.38

06

.85

19

.17

7A

sph

amin

2.4

39

6.0

01

7.9

78

0.0

44

2.5

14

5.5

01

7.1

85

2.3

72

6.7

01

8.7

77

Ev

oth

erm

2.4

39

6.0

01

7.7

78

0.0

20

2.4

86

5.8

51

7.3

80

2.3

82

6.7

51

8.7

76

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these mixtures were found to be less than minimum 6%

binder content requirement as per the AASHTO require-

ment (AASHTO 2008). Also, surface of aggregate B is

smoother with very less irregular faces. Due to lesser

surface area, these mixtures required lower asphalt binder

content than the other two aggregate source asphalt

mixtures at the design air voids levels. The VCADry voids

in coarse aggregate (VCA) values observed for aggregates

A, B and C were 41.88%, 41.52% and 42.35%,

respectively. VCAMix for all the mixtures were found to

be lower than VCADry. Mixture design test results

indicated that as the percentage of rubber content

increased, the OBCs in the mixtures also slightly increased.

As reported earlier, it was observed that due to increased

viscosity, more modified binder was required to achieve

the target air void of the mixture at the specified mixing and

compaction temperatures (Bahia and Davis 1994).

3.2 Draindown test results

Draindown was tested at OBCs for all the mixtures as per

AASHTO T 305-2001, and the test results are shown in

Table 5. Mixtures were tested at respective production

temperatures plus 158C for both virgin and WMA

mixtures. No fibres were used for rubberised asphalt

mixtures, whereas cellulose fibres were used for mixtures

with binder PG 76-22. It was observed that the draindown

values increased slightly as the binder contents increased

in the asphalt mixture. Most states require that the

draindown of SMA mixtures does not exceed 0.3% by

weight of mixture. There was no significant difference in

the draindown property of all the mixtures, and all the

mixtures showed draindown values lower than the

specification requirement of 0.3%.

3.3 Dry ITS analysis

From the statistical analysis data, for mixtures with 20%

rubberised asphalt made with aggregate C, the dry ITS

values were found to be higher than for mixtures made

with aggregate A and B. From Table 6, it was observed

that for all other mixtures, no significant difference was

reported for the dry ITS values using different binder and

aggregate types. There were significant differences

observed for dry ITS values between virgin mixtures and

mixtures containing Sasobitw using binders with 10 and

15% CR content. Significant differences were also

observed for mixtures containing Sasobitw when com-

pared with mixtures containing Asphaminw using 15%

CR content. Mixtures with Evothermw additive using

15% rubber content also were significantly different from

mixtures with virgin binder and Asphamin with respect to

dry ITS values (with aggregates A and B). From Figure

1(a),(b), it is observed that virgin mixtures showed Tab

le6

.S

tati

stic

alan

aly

sis

for

agg

reg

ate

sou

rces

A,

Ban

dC

and

bin

der

typ

esu

sed

.

Ag

gre

gat

eso

urc

e(A

,B

,an

dC

)

Dry

ITS

Wet

ITS

Dry

tou

gh

nes

sW

etto

ug

hn

ess

Dry

def

orm

atio

nW

etd

efo

rmat

ion

a¼

0.0

5A,

BB,

CA,

CA,

BB,

CA,

CA,

BB,

CA,

CA,

BB,

CA,

CA,

BB,

CA,

CA,

BB,

CA,

C

PG

64

-22þ

10

%C

RN

SN

SN

SN

SN

SS

NS

NS

NS

NS

NS

NS

NS

NS

NS

NS

NS

NS

PG

64

-22þ

15

%C

RN

SN

SN

SN

SN

SS

NS

NS

NS

NS

NS

NS

NS

NS

NS

NS

NS

NS

PG

64

-22þ

20

%C

RN

SS

SN

SN

SS

NS

SS

NS

NS

SN

SN

SN

SN

SN

SN

S

PG

76

-22þ

fib

res

NS

NS

NS

NS

NS

SN

SN

SN

SN

SN

SN

SN

SN

SN

SS

NS

NS

Note

:S

,P

-val

ue,

a¼

0.0

5(s

ignifi

cant

dif

fere

nce

)an

dN

S,P

-val

ue.

a¼

0.0

5(n

osi

gnifi

cant

dif

fere

nce

).

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comparatively improved dry ITS values for aggregates A

and B, when compared with mixtures with Asphaminw

and Evothermw additive. Mixtures with Asphaminw and

Evothermw additives showed an increase in the dry ITS

values compared with virgin mixtures using 15% CR

content. Dry ITS values of mixtures with Asphaminw

were found to be higher than virgin mixtures when PG 76-

22 binder was used with aggregate B or with aggregate

C. The dry ITS values for all the SMA mixtures were

greater than 500 kPa. The lowest dry ITS value was

observed for mixtures with aggregate B using Evothermw

additive with 10% CR content. The highest dry ITS value

came from a mixture using aggregate B with PG 76-22 and

containing Sasobitw. In general, lower dry ITS values

were observed for mixtures with Asphaminw or

Evothermw additives for aggregate A and B, respect-

ively. The dry ITS values of specimens made from

aggregate C showed no significant change due to higher

OBCs compared with those of mixtures with and without

WMA using aggregate sources A and B, thereby

increasing the durability of the mixtures. With respect to

the WMA additive effects, based on the statistical analysis,

6 of 24 combinations showed significant difference in the

dry ITS values.

3.4 Wet ITS analysis

From Figure 1, it is observed that all the mixtures met the

minimum wet ITS requirement of 448 kPa (65 psi) as per

SCDOT requirements. From Figure 1(a),(c), it can be seen

that wet ITS values for mixtures made from aggregate C

were significantly higher than those of mixtures with

aggregate A. As per Table 6, no significant difference in

wet ITS values were observed between any two mixtures

from aggregates A and B or between aggregates B and

C. From Figure 1(a), for the aggregate source A, the

mixtures with Asphaminw show the lowest wet ITS values

out of all the mixtures. For aggregate B, mixtures with

Evothermw additive showed lower wet ITS values than all

other mixtures. For aggregate C, higher wet ITS values

were observed for virgin mixtures using 20% CR content

and for mixtures using PG 76-22 binder containing

Sasobitw additive as shown in Figure 1(c). The mixtures

with PG 76-22 binder showed the highest wet ITS value

than other mixtures in this study. For mixtures with 15%

CR content, wet ITS values were found to be significantly

higher for mixtures containing Sasobitw than mixtures

with Asphaminw. From Figure 1, it is observed that virgin

mixture and mixtures with Sasobitw showed improved

wet ITS values than mixtures containing Asphaminw.

From Table 7, it can be seen that no significant difference

was observed for wet ITS values for mixtures between

Sasobitw, Asphaminw and Evothermw. With respect to

the WMA additive effects, based on the statistical analysis,

only 2 of 24 mixtures showed significant difference in wet

ITS values amongst all the three types of WMA additives

(control, Asphaminw, Sasobitw and Evothermw), show-

ing that the addition of WMA additives while working at

0

200

400

600

800

1000

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

PG 64-22+10% CR

PG 64-22+15%CR

PG 64-22+20%CR

PG 76-22+Fibers

Binder type

ITS

(kP

a)Dry Wet

0

200

400

600

800

1000

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

PG 64-22+10%CR

PG 64-22+15%CR

PG 64-22+20%CR

PG 76-22+Fibers

Binder type

ITS

(kP

a)

Dry Wet(a) (b)

0

200

400

600

800

1000

PG 64-22+10%CR

PG 64-22+15%CR

PG 64-22+20%CR

PG 76-22+Fibers

Binder type

ITS

(kP

a)

Dry Wet(c)

Figure 1. ITS values of specimens made with aggregate sources (a) A, (b) B and (c) C.

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Tab

le7

.S

tati

stic

alan

aly

sis

for

vir

gin

and

mix

ture

sw

ith

WM

Aad

dit

ives

.

Ag

gre

gat

eso

urc

e(A

,B

,an

dC

)

Dry

ITS

Dry

tou

gh

nes

sD

ryd

efo

rmat

ion

WM

AT

yp

e(1

-Vir

gin

;2

-Sas

ob

it;

3-A

sph

min

;4

-Ev

oth

erm

)

a¼

0.0

51,

22,

31,

32,

41,

43,

41,

22,

31,

32,

41,

43,

41,

22,

31,

32,

41,

43,

4

PG

64

-22þ

10

%C

RS

NS

NS

NS

NS

NS

NS

SN

SN

SN

SN

SN

SS

NS

NS

NS

NS

PG

64

-22þ

15

%C

RS

SN

SN

SS

SN

SN

SS

NS

NS

NS

NS

NS

NS

NS

NS

NS

PG

64

-22þ

20

%C

RN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SS

NS

SN

SN

SN

S

PG

76

-22þ

fib

res

NS

NS

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SS

NS

a¼

0.0

5W

etIT

SW

etto

ug

hn

ess

Wet

def

orm

atio

n

PG

64

-22þ

10

%C

RN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

S

PG

64

-22þ

15

%C

RN

SS

NS

NS

NS

NS

NS

NS

NS

NS

NS

NS

SN

SS

NS

SN

S

PG

64

-22þ

20

%C

RN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SS

NS

NS

S

PG

76

-22þ

fib

res

NS

NS

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

SN

S

Note

:S

,P

-val

ue,

a¼

0.0

5(s

ignifi

cant

dif

fere

nce

)an

dN

S,

P-v

alue.

a¼

0.0

5(n

osi

gnifi

cant

dif

fere

nce

).

P.V. Shivaprasad et al.158

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lower temperatures does not negatively affect the wet ITS

values for the mixtures studied. Many studies in the past

have shown that the chemical and physical properties of

aggregates play an important role in determining the anti-

stripping resistance of the mixtures (Bahia and Davis

1994, Gandhi 2008, Xiao and Amirkhanian 2008). On the

other hand, the addition of anti-stripping additives (e.g.

hydrated lime) used in the present study plays an

extremely important role in improving the resistance to

moisture susceptibility of the mixtures.

3.5 TSR analysis

The TSR results are presented in Figure 2. Test results

indicated that 13 out of 48 mixtures failed to meet the TSR

requirement of 85% as per SCDOT specifications. For

mixtures with aggregate B alone, six mixtures failed to

meet the TSR requirement. One of the probable reasons

might be due to lower asphalt binder contents for mixtures

from aggregate B as compared with other mixtures using

aggregate sources A and C. Also, lower TSRs may be

attributed to the reduction in binder ageing at the lower

production temperatures.

Test results revealed that 7 of 13 mixtures which failed

to meet the minimum TSR requirement contained

Asphaminw. It seems that Asphaminw may have a

negative effect in resisting moisture damage for the

materials tested in this study. Two virgin mixtures and two

Evothermw mixtures (with 10% CR content and with PG

76-22 binder) failed to meet the TSR requirement. All the

mixtures containing Sasobitw additive met the minimum

TSR requirement.

Test results indicated that 6 out of 16 mixtures using

aggregate B failed to meet the TSR requirement of 85% as

shown in Figure 2. Results show that even though by using

2% hydrated lime as antistripping agent, 37% of the SMA

mixtures using aggregate B failed to meet the TSR

requirement of 85%, thereby indicating significant

reduction in the TSR values observed for mixtures using

aggregate B as compared with mixtures using aggregates

A and C. It can be concluded that aggregate plays an

important role in understanding the resistance to moisture

susceptibility of the SMA mixtures using different WMA

additives.

In Figure 2, some TSR values are extremely high (i.e.

higher than 120%). These mixtures were conditioned and

contained 2% hydrated lime. Again, due to the aggregate

properties, it seems that the bond between aggregate and

binder becomes stronger when the specimens were

conditioned in a 608C water bath even though the air

voids of two type specimens were almost identical. Results

showed that three out of four mixtures failed to meet the

TSR requirement for mixtures with 10% CR content. In

order to improve the TSR values, it is recommended to

increase the anti-stripping additive percentage for

mixtures using 10% CR content.

3.6 Aggregate chemical composition on moisturedamage of mixtures

The chemistry of the aggregate surface affects the degree

of the water sensitivity of the asphalt–aggregate bond. As

per Table 1, the chemical composition of aggregate B

(marble schist) indicates presence of higher CaO content

in the aggregate than the other two aggregates (A and C).

The presence of higher CaO (%) and lower SiO2 (%)

should improve better resistance to moisture susceptibility

of mixtures. Marble schist aggregate is considered to bear

a positive charge and usually stronger bonds are associated

with more electro-positive charge. On the contrary to this

point, TSR test results showed that even though by adding

2% hydrated lime as antistripping agent, 37% of the

–40

–20

0

20

40

60

80

100

120

140

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

PG 64-22+10% CR PG 64-22+15% CR PG 64-22+20% CR PG 76-22+Fibers

Binder type

TSR

(%

) an

d P

TL

(%

)

TSR (%) Aggregate A TSR (%) Aggregate B TSR (%) Aggregate C

PTL (%) Aggregate A PTL (%) Aggregate B PTL (%) Aggregate C

Min. TSR-85%

Figure 2. TSR and PTL values for mixtures made from aggregate sources A, B and C.

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mixtures using aggregate B failed to meet the TSR

requirement. It can be concluded that adding more lime

content (2%) was found to be detrimental to aggregate

type B in improving resistance to moisture damage of

mixtures while considering the chemical composition of

this aggregate. As mentioned before, one other possible

reason might be due to lower asphalt binder contents for

mixtures from aggregate B than other mixtures using

aggregate sources A and C. The other two sources of

aggregates, A and C, belonged to granite type and these

aggregates consisted of higher contents of Al2O3 (%) and

SiO2 (%). Silica usually causes a reduction in the bond

between asphalt and aggregate. This makes the granite

aggregate fall under the hydrophilic category. TSR test

results indicated that 25% of the mixtures failed using

aggregate A containing micaceous granite, whereas 12.5%

of the mixtures failed using aggregate C containing

crushed granite. Overall, the study indicated that

considering the aggregate chemical composition and

TSR results, it seems like mixtures with aggregate C are

found to be less prone to moisture-induced damage than

other two selected aggregate types.

3.7 Wet deformation analysis

The deformation (flow) resistance of wet ITS specimens, a

measure of the material’s resistance to permanent

deformation in service (Xiao and Amirkhanian 2008),

was used for moisture susceptibility analysis of the mixture.

The wet deformation results indicated that, in general, the

moisture in the aggregate resulted in an increase in the

deformation (flow) value. From Figure 3(a),(b), test results

indicate that the specimens made with PG 76-22 using

aggregate source B showed significantly higher wet

deformation values than specimens with aggregate A. The

specimens made with aggregate sources A and C showed

relatively consistent wet deformation values in the range of

2.4–3.8 mm, whereas for mixtures with aggregate B, the

wet deformation values varied from 2 to 5.4 mm, indicating

that distorting and shoving may be easier to occur in the

mixtures using aggregate B. Another contributing factor for

higher deformation in mixtures with aggregate B may be

that the aggregates are smoother with very few irregula-

rities, leading to more distortion of aggregates in the

mixture.

With respect to the WMA additive effects, 5 of 24

combinations showed significant difference in the wet

deformation values (Table 7). The wet deformation values

observed for mixtures with Sasobitw, Asphaminw and

Evothermw were found to be significantly higher than the

virgin mixtures using PG 64-22 with 15% CR content.

Similarly, mixtures with Asphaminw had higher defor-

mation values than virgin mixtures, indicating that

mixtures with Asphaminw had greater potential to wet

deformation than virgin mixtures. Also, mixtures contain-

ing Asphaminw had higher wet deformation values than

mixtures with Evothermw additive for all the binder types

that were tested. From Figure 3, it is concluded that,

considering WMA additives, SMA mixtures with Saso-

0123456(a) (b)

(c)

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

PG 64-22+10%CR

PG 64-22+15%CR

PG 64-22 +20%CR

PG 76-22+Fibers

PG 64-22+10%CR

PG 64-22+15%CR

PG 64-22 +20%CR

PG 76-22+Fibers

Binder type Binder type

Def

orm

atio

n (m

m)

Dry Wet

0123456

Def

orm

atio

n (m

m)

Dry Wet

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

PG 64-22+10%CR

PG 64-22+15%CR

PG 64-22 +20%CR

PG 76-22+Fibers

Binder type

0

1

2

3

4

5

6D

efor

mat

ion

(mm

)Dry Wet

Figure 3. Deformation values of ITS specimens made with aggregate sources (a) A, (b) B and (c) C.

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bitw showed lower wet deformation values than mixtures

containing Evothermw and Asphaminw.

3.8 Dry deformation analysis

Based on the statistical analysis, it was observed that there

was no significant difference in dry deformation values

with respect to the aggregates A, B and C with all types of

binders (Table 6). Mixtures with Sasobitw showed lower

dry deformation values than mixtures containing Aspha-

minw with asphalt binder with 10% CR content. From

Figure 3, it is observed that the dry deformation values for

virgin mixtures were found to be lower than mixtures with

Sasobitw and Asphaminw using asphalt binder with 20%

CR content. The mixtures containing Evothermw also

showed higher dry deformation values than virgin

mixtures using PG 76-22 binder.

3.9 Wet toughness analysis

Toughness was defined as the area under the tensile stress–

deformation curve up to a deformation of twice that

incurred at maximum tensile stress (Xiao and Amirkhanian

2008). The toughness results of wet ITS specimens are

shown in Figure 4, and statistical analysis is presented in

Table 3. From Figure 4(a),(c), it is observed that the wet

toughness values for mixtures made from aggregate C were

relatively higher than for mixtures made with aggregate A

using asphalt binder with 20% CR content. No significant

difference was observed with respect to wet toughness

values for all the mixtures studied for all three aggregates

sources (A, B and C). With respect to effect of WMA

additives on wet toughness, no significant difference was

observed for any of the mixtures investigated.

3.10 Dry toughness analysis

From Figure 4, it is observed that the dry toughness values

of the virgin (HMA) mixtures showed lower dry toughness

values than for mixtures containing WMA additives

regardless of the aggregate source. From Figure 4, it is

observed that the dry toughness values for aggregate C were

found to be higher than mixtures made from aggregates A

and B using asphalt binder with 20% CR content. Apart

from this, all other mixtures showed no significant

difference in dry toughness values with respect to aggregate

sources A, B and C and selected binder types (Table 6). The

dry toughness values for mixtures containing Asphaminw

were found to be higher than toughness values for mixtures

containing Sasobitw using asphalt binder with 10% CR

content. Similarly mixtures with Asphaminw had higher

toughness values than virgin mixtures using asphalt binder

with 15% CR content. Apart from this, all other mixtures

showed no significant difference in the dry toughness

values with respect to WMA additives.

3.11 PTL analysis

As shown in Equation 1, the PTL values were positive due

to dry toughness values being greater than wet toughness

values. Figure 2 shows that, in most cases, the PTL values

were found to be positive. However, 13 of 48 mixtures

0

2

4

6To

ughn

ess

(N/m

m)

0

2

4

6(b)(a)

Toug

hnes

s (N

/mm

)

Dry Wet Dry Wet

Binder type

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Evo

ther

m

PG 64-22+10%CR

PG 64-22+15%CR

PG 64-22 +20%CR

PG 76-22+Fibers

Binder type

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Evo

ther

m

PG 64-22+10%CR

PG 64-22+15%CR

PG 64-22 +20%CR

PG 76-22+Fibers

(c)

0

2

4

6

Toug

hnes

s (N

/mm

)Dry Wet

Binder type

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Vir

gin

Saso

bit

Asp

ham

in

Vir

gin

Saso

bit

Asp

ham

in

Evo

ther

m

Evo

ther

m

PG 64-22+10%CR

PG 64-22+15%CR

PG 64-22 +20%CR

PG 76-22+Fibers

Figure 4. Toughness values for mixtures made with aggregate sources (a) A, (b) B and (c) C.

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showed negative PTL values, indicating that the wet

toughness values from these specimens were higher than

the dry toughness values. Mixtures with Sasobitw showed

maximum number of specimens showing negative PTL

values, indicating that these mixtures showed better

resistance to toughness loss than other mixtures tested.

Virgin and mixtures with Evothermw showed a similar

number of samples showing negative PTL values, whereas

mixtures with Asphaminw showed the least number of

samples showing negative PTL values, indicating that

these mixtures were prone to moisture damage. In general,

the mixtures made from aggregate B showed lower PTL

values than mixtures made from aggregates A and C.

4. Frequency distribution analysis of its test results

To further study the effects of aggregate source, binder

type and WMA additive on resistance to moisture

susceptibility, frequency distribution analysis was done

in terms of ITS for the mixtures studied. The distribution

analysis of the mixtures was categorised into dry and wet

groups. Figure 5(a),(b) show the influence of three

different aggregate sources studied. From Figure 5(a), it

can be seen that the peak dry ITS distribution was

observed for aggregate A and the range of the dry ITS

observed was between 700 and 800 kPa, followed by

aggregates B and C, showing a range between 800 and

900 kPa and between 600 and 700 kPa, respectively. For

the wet specimens (Figure 5(b)), the peak distribution was

observed for aggregate B having a range between 600 and

700 kPa, followed by aggregate C having a range between

500 and 600 kPa. Lowest peak ITS values were observed

for the wet specimens for mixtures using aggregate

A. From the present analysis, it can be concluded that in

general, for the wet specimens irrespective of the

aggregate source studied, the wet ITS values observed

0

10

20

30

40

50(a) (b)

(d)(c)

(e) (f)

300-400

400-500

500-600

600-700

700-800

800-900

900-1000

1000-1100

300-400

400-500

500-600

600-700

700-800

800-900

900-1000

1000-1100

ITS range for dry sample (kPa)

300-400

400-500

500-600

600-700

700-800

800-900

900-1000

1000-1100

ITS range for dry sample (kPa)

300-400

400-500

500-600

600-700

700-800

800-900

900-1000

1000-1100

ITS range for dry sample (kPa)

Fre

quen

cy (

%)

0

10

20

30

40

50

Fre

quen

cy (

%)

Aggregate AAggregate BAggregate C

ITS rangefor wet sample (kPa)

300-400

400-500

500-600

600-700

700-800

800-900

900-1000

1000-1100

ITS rangefor wet sample (kPa)

300-400

400-500

500-600

600-700

700-800

800-900

900-1000

1000-1100

ITS rangefor wet sample (kPa)

Aggregate AAggregate BAggregate C

0

10

20

30

40

50

60

Fre

quen

cy (

%)

0

10

20

30

40

50

60

Fre

quen

cy (

%)

PG 64-22+10% CRPG 64-22+15% CRPG 64-22+20% CRPG 76-22+Fibers

PG 64-22+10% CR PG 64-22+15% CRPG 64-22+20% CR PG 76-22+Fibers

0

10

20

30

40

50

Fre

quen

cy (

%)

0

10

20

30

40

50

Fre

quen

cy (

%)

VirginSasobit

AsphaminEvotherm

Virgin

Sasobit

As phamin

Evotherm

Figure 5. Frequency distribution curves for indirect tensile strength tests for mixtures (a, b) aggregate effect (b, c) binder effect and (c,d) WMA effect.

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for SMA mixtures were in the range between 500 and

900 kPa. Figure 5(c),(d) show the influence of binder type

used in the present investigation. Figure 5(c) shows that

the peak distribution values were observed for dry

specimens with PG 64-22 þ 10% CR binder (between

700 and 800 kPa), followed by specimens with PG 64-

22 þ 20% CR in the same ITS range level. For the

mixtures with PG 64-22 þ 15% CR, the peak ITS range

observed was between 700 and 800 kPa, whereas for

mixtures with PG 76-22 þ fibres showed the lowest peak

frequency distribution (between 900 and 1000 kPa).

Figure 5(d) shows that the peak ITS distribution for wet

specimens was observed for mixtures with PG 64-

22 þ 10% CR ranging between 500 and 600 kPa, followed

by specimens with PG 64-22 þ 15% CR ranging between

600 and 700 kPa. All the mixtures met the minimum wet

ITS requirement of SCDOT specifications of 448 kPa

(65 psi). Based on the wet ITS peak distribution, the

mixtures with PG 64-22 þ 10% CR binder showed the

least resistance to moisture susceptibility than all other

mixtures studied. The mixtures with PG 64-22 þ 20% CR

showed improved peak wet ITS distribution ranging

between 700 and 800 kPa. The range of the wet ITS values

observed for mixtures with PG 76-22 þ fibres was in the

range of 800–900 kPa, indicating better resistance to

moisture-induced damage than all other mixtures inves-

tigated in the present study. Figure 5(e),(f) show that the

influence of WMA additive on the moisture susceptibility

properties of the mixtures. Figure 5(e) shows that mixtures

with Evothermw showed the highest peak dry ITS

frequency distribution compared with all other mixtures

studied. The dry peak ITS value observed for mixtures

with Evothermw was between 700 and 800 kPa followed

by virgin mixtures having values in the same ITS range.

The peak dry ITS range observed for mixtures with

Asphaminw and Sasobitw were between 800 and 900 kPa

and between 700 and 800 kPa, respectively. Mixtures with

Sasobitw showed the least peak dry ITS value compared

with all other mixtures studied. In general, the dry peak

ITS values observed for WMA mixtures ranged between

400 and 1000 kPa with respect to the WMA type, binder

type and the aggregate used in this investigation.

Figure 5(f) shows that peak wet ITS range observed for

mixtures with Evothermw was between 600 and 700 kPa,

indicating the possibility of lower resistance to moisture

susceptibility than all other mixtures studied. The peak wet

ITS range for virgin and for mixtures with Asphaminw

was observed to be in the range between 700 and 800 kPa.

The mixtures with Sasobitw showed the lowest peak wet

ITS values (between 500 and 1000 kPa).

Considering the effect of WMA type, it can be

concluded that based on the frequency distribution

analysis, mixtures with Sasobitw showed the least dry

and wet ITS range, thereby indicating better resistance

to moisture-induced damage than all other mixtures

investigated. Furthermore, cumulative frequency distri-

bution (CFD) analysis was carried out for mixtures (Figure

6), to study the effect of different types of aggregate,

binder and WMA additive on moisture susceptibility of

mixtures. To study the effect of aggregate, Figure 6(b)

shows that for mixtures containing aggregate A, 3% of

CFD showed wet ITS values ranging between 400 and

500 kPa. In addition, to study the effect of binder type,

Figure 6(d) shows that for mixtures with PG 64-22 þ 20%

CR, 4% of CFD showed wet ITS values ranging between

400 and 500 kPa. Furthermore, to study the effect of

WMA, Figure 6(f) shows that for mixtures with Evotherm,

4% of CFD showed wet ITS values ranging between 400

and 500 kPa.

5. Findings

The following findings were drawn based on the

experimental test results obtained from the laboratory

investigation on various SMA mixtures containing WMA

additives:

. No significant difference in the draindown proper-

ties were observed for virgin and mixtures with

WMA additives. Considering the effect of WMA

additives, 25% of mixtures investigated showed

significant difference in the dry ITS values. The

lowest dry ITS value was observed for mixtures

made from aggregate B containing Evothermw and

asphalt binder with 10% CR content. Mixtures made

from aggregate B using PG 76-22 þ fibres and

Sasobitw showed the highest dry ITS value as

compared with all other selected mixtures.. No significant difference in the wet ITS values was

observed between the mixtures using aggregates A

and B or between aggregates B and C. Mixtures with

PG 76-22 þ fibres showed higher wet ITS value

than all other mixtures. The lowest wet ITS values

were observed for mixtures made from aggregate-

source A containing Asphamin (R), and aggregate

source B containing Evotherm (R) additive,

respectively. No significant difference was observed

in wet ITS values between mixtures with Sasobitw

and Asphaminw or between mixtures with Aspha-

minw and Evothermw.. Test results showed that 53% of mixtures which

failed to meet the minimum TSR requirement were

the mixtures containing Asphaminw additive. All

the mixtures using Sasobitw additive met the

minimum TSR requirement of 85%. Majority of

the mixtures investigated showed an increase in

TSR values indicating that these mixtures do not

cause a decrease in strength due to the intrusion of

water into the mixture. Results show that even

though by using 2% hydrated lime as antistripping

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agent, 37% of the mixtures using aggregate B failed

to meet the TSR requirement of 85%.. With respect to WMA additives, mixtures with

Sasobitw showed lower wet deformation values than

mixtures containing Evothermw and Asphaminw. No

significant difference was observed with respect to

wet toughness values for all the mixtures made from

the aggregate sources A, B and C and considering all

the selected types of binders. With respect to effect of

WMA additives on wet toughness, no significant

difference was observed for any mixture.. Frequency distribution analysis showed that the

lowest wet ITS range was observed for mixtures

with PG 76-22 þ fibres ranging between 700 and

800 kPa, indicating better resistance to moisture

damage. In addition, the cummulative distribution

curve of mixtures with Sasobitw showed the least dry

and wet ITS value range (400 to 1000 kPa), thereby

indicating better resistance to moisture susceptibility

than all other selected mixtures.

6. Conclusions

The test results indicated that, in general, the use of WMA

additives in SMA mixtures containing 2% hydrated lime

(by weight of the aggregate) improved the resistance of the

mixtures to moisture susceptibility. However, as sus-

pected, aggregate source plays an important role in

understanding the resistance to moisture susceptibility of

the SMA mixtures using different WMA additives. In

general, the mixtures made with PG 76-22 plus fibres

produced better resistance to moisture damage. The

mixtures containing over 15% rubber (by weight of virgin

binder) produced similar resistance to moisture suscepti-

bility compared with mixtures made with PG 76-

22 þ Fibres. Thus enabling asphalt industry to use

ITS range for wet sample (kPa)

0

20

40

60

80

100(a) (b)

(c) (d)

(e) (f)

Cum

mul

ativ

efr

eque

ncy

(%)

0

20

40

60

80

100

Cum

mul

ativ

efr

eque

ncy

(%)

0

20

40

60

80

100

Cum

mul

ativ

efr

eque

ncy

(%)

0

20

40

60

80

100

Cum

mul

ativ

efr

eque

ncy

(%)

0

20

40

60

80

100

Cum

mul

ativ

efr

eque

ncy

(%)

A B C

PG 64-22+10% CRPG 64-22+15% CRPG 64-22+20% CRPG 76-22+Fibers

PG 64-22+10% CRPG 64-22+15% CRPG 64-22+20% CRPG 76-22+Fibers

Virgin

SasobitAsphamin

Evotherm

VirginSasobitAsphaminEvotherm

300-400

400-500

500-600

600-700

700-800

800-900

900-1000

1000-1100

300-400

400-500

500-600

600-700

700-800

800-900

900-1000

1000-1100

ITS range for wet sample (kPa)

300-400

400-500

500-600

600-700

700-800

800-900

900-1000

1000-1100

0

20

40

60

80

100

Cum

mul

ativ

efr

eque

ncy

(%)

ITS range for wet sample (kPa)

300-400

400-500

500-600

600-700

700-800

800-900

900-1000

1000-1100

ITS range for dry sample (kPa)

300-400

400-500

500-600

600-700

700-800

800-900

900-1000

1000-1100

ITS range for dry sample (kPa)

300-400

400-500

500-600

600-700

700-800

800-900

900-1000

1000-1100

ITS range for dry sample (kPa)

A B C

Figure 6. CFD curves for indirect tensile strength tests for mixtures (a, b) aggregate effect (b, c) binder effect and (c, d) WMA effect.

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rubberised SMA with WMA additives containing over

15% CR with no fibres instead of using PG 76-22 þ fibres

resulting in major cost savings. Field evaluation of SMA

test sections using different warm mix technologies is

necessary to better understand the long-term performance

of such pavements for the varying climatic and traffic

conditions.

Acknowledgements

The authors would like to thank Dr E. Ray Brown for giving hisvaluable inputs and suggestions for this research project.Financial support was possible through a grant from SouthCarolina Department of Health and Environment Control(DHEC) and the Asphalt Rubber Technology Service (ARTS)of Clemson University.

Notes

1. Email: feipenx@clemson.edu2. Email: serji.amirkhanian@gmail.com

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