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Materials and Structures ISSN 1359-5997 Mater StructDOI 10.1617/s11527-015-0566-x

Estimating the moisture damage of asphaltmixture modified with nano zinc oxide

Gholam Hossein Hamedi, FereidoonMoghadas Nejad & Khosro Oveisi

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ORIGINAL ARTICLE

Estimating the moisture damage of asphalt mixture modifiedwith nano zinc oxide

Gholam Hossein Hamedi • Fereidoon Moghadas Nejad •

Khosro Oveisi

Received: 3 November 2014 / Accepted: 9 February 2015

� RILEM 2015

Abstract One of the main distresses of hot mix

asphalt (HMA) is moisture damage. The most common

method for decreasing this type of distress is using

antistrip additives. In this study, the effect of nano-

particles was evaluated as an antistrip agent on the

moisture damage of HMA. Two types of aggregates

were evaluated in this study with different sensitivities

against moisture damage (limestone and granite

aggregate) and the asphalt binder with 60/70 penetra-

tion grade and nano zinc oxide (ZnO) in two different

percentages by weight of the asphalt binder. The tests

employed to evaluate the effects of modifying asphalt

binder by nanomaterials on the moisture damage of

asphalt mixture were surface free energy (SFE) and

AASHTO T283. The results showed that the ratio of

wet/dry values of indirect tensile strength for the

mixtures containing nano ZnO for two types of

aggregate were higher than the control mixtures. In

addition, the results of the SFE method showed that

adding nano ZnO increased the total SFE of the asphalt

binder, which led to better coating of the aggregate with

asphalt binder. Nano ZnO decreased the acid to base

ratio of SFE of asphalt binder, while it led to improving

adhesion between the asphalt binder and acidic

aggregate that are prone to moisture damage.

Keywords Hot mix asphalt � Moisture damage �Nanomaterials � Surface free energy � AASHTO T283

1 Introduction

Numerous highway agencies have been experiencing

premature failures of asphalt mixture layers, which

decrease the performance and service life of pave-

ments. Moisture damage is one of the major problems

that can be faced by a pavement during its service life.

It can tremendously reduce a pavement’s strength and

consequently its life [1, 2]. Whether stripping occurs

prematurely or in a reasonable range of service life, the

required repair costs could probably be reduced

through judicious material selection [3]. The extent

of moisture damage, called moisture susceptibility as

well, depends on internal and external factors. The

external factors include environmental conditions,

production and construction practices, pavement

design, and traffic level, while the internal factors

are related to the properties of the materials and the

microstructure distribution [4]. A number of mechan-

isms are identified in the literature, which are

responsible for adhesion and debonding between the

asphalt binder and aggregate. The majority of these

mechanisms are based on physio-chemical interac-

tions between the asphalt binder and the aggregate,

which could be classified into the following three

broad categories: (1) mechanical adhesion, (2) physi-

cal adhesion, and (3) chemical bonding [5].

G. H. Hamedi � F. M. Nejad (&) � K. Oveisi

Amirkabir University of Technology, Tehran, Iran

e-mail: moghadas@aut.ac.ir

Materials and Structures

DOI 10.1617/s11527-015-0566-x

Author's personal copy

Water affects asphalt pavements in a detrimental

way and it is common knowledge that certain

combinations of binder and aggregate can trigger

premature failures [6]. To improve moisture damage

of the asphalt mixture, there are several methods. The

most common method for controlling moisture

damage of asphalt mixtures is using the antistrip agent

[7]. Two general categories of antistrip agents have

become apparent in order to improve adhesion and

reduce moisture sensitivity in asphalt mixtures. The

first category suggests the aggregate surface to be

coated by a suitable agent, which will reverse the

predominant electrical charges at the surface and thus

reduce the surface energy of the aggregate. The second

approach is changing the surface energy of the asphalt

binder with suitable agents and giving an electrical

charge opposite to that of the aggregate surface [8].

Numerous laboratory tests have been developed over

the years to identify the effect of antistrip agents on

moisture sensitivity of HMA. Nowadays, water sensitiv-

ity of asphalt pavements is investigated using rather

simple tests which can be subdivided in two groups: those

performed on loose mixtures, such as the static

immersion, and those performed on compacted mixtures,

such as modified lottman [9, 10]. Traditional methods to

assess moisture sensitivity of asphalt mixes rely on

mechanical tests that evaluate the mix as a whole. These

methods do not independently measure material proper-

ties and their role in the moisture sensitivity of the mix

[5]. It is necessary to understand the mechanisms that

cause moisture damage and, consequently, to know how

to select materials in an asphalt mixture with high

resistance to moisture damage. There is a need for simple

and repeatable tests that can evaluate the multifunctional

aspects of pavement performance in the presence of

moisture [11].

SFE focuses on the evaluation of the susceptibility

of aggregates and asphalts to moisture damage

through understanding the micro-mechanisms that

influence the adhesive bond between aggregates and

asphalt and the cohesive strength and durability of the

asphalt binder in dry and wet conditions [12]. SFE is

defined as the energy needed to create a new unit

surface area of material in vacuum conditions. The

summation of these interfacial interactions is the

thermodynamic work of adhesion, which quantifies

the energy available for adhesion based on the

energetic properties of two interacting surfaces [13].

The work of adhesion and surface energies play a vital

role in adhesion and in understanding theories of

adhesion. Even modest changes in their values can

cause large changes in the measured adhesion [14].

1.1 Literature review

There are various modelling methods for evaluation

the mechanisms of moisture damage of asphalt mix-

tures but the paper’s focus is on experimental methods.

Cheng et al. [15] conducted a comprehensive study on

the SFE concept, measurement and its applications in

asphalt pavement. They proposed two moisture dam-

age models based on major moisture failure mechan-

isms and then conducted mechanical experiments on

sand asphalt and asphalt mixtures, and their results

showed excellent agreement with the models. Hefer

[16] pursued the optimization of techniques to charac-

terize SFE, as well as the consideration and evaluation

of additional factors that influence adhesion in the

presence of water. They presented a synthesis of

theories and mechanisms of asphalt binder–aggregate

adhesion, and existing and potential techniques for

SFE characterization were reviewed to establish firm

background knowledge on this subject. Zollinger [17]

assessed moisture damage susceptibility using SFE

measurements and dynamic mechanical analysis

(DMA). DMA testing was used to evaluate the rate of

damage accumulation in asphalt binders and mastics.

Kim et al. [18] used the percentage of the surface area

of aggregate that has been exposed to water as a

significant index to quantify the level of adhesive

fracture. This index is calculated with the surface free

energies of aggregate and asphalt which are measured

by two methods, the universal gas adsorption and the

Wilhelmy plate, respectively. Howson et al. [19]

developed a database of SFE measurements. This

database will be useful as a diagnostic tool for finding

the cause of poor moisture damage resistance in mixes

and to suggest remedies through modification with

antistrip additives, lime, polymers, other additives, or

through a change of materials in extreme cases.

There has been an increasing amount of literature on

evaluating the effect of antistrip additives on moisture

damage of HMA with the thermodynamic concept, in

recent years. With both laboratory tests and a proposed

chemical model of asphalt binder based on its SFE

characteristics, Wasiuddin et al. [20] evaluated the

effect of antistrip additives on asphalt binders. The

results of this study showed that the dynamic Wilhelmy

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plate method is an excellent tool for evaluating total

SFE and acid–base components of SFE of asphalt

binders with and without antistrip additives. Wasiuddin

et al. [21] evaluated the SFE characteristics of two

types of aggregates in a separate study, with and

without styrene–butadiene rubber (SBR) treatment for

moisture-induced damage potential. SBR coating

changed the aggregate surface from hydrophilic to

hydrophobic and thus increased the wettability of the

asphalt binder on the aggregate. In 2010, Arabani and

Hamedi [22] published a paper in which they expressed

the role of aggregate treatment on moisture damage of

HMA. The result of this study demonstrated that

aggregate coating with polyethylene increases the

wettability of asphalt binder on the aggregate and the

adhesion between the asphalt binder and aggregate.

Comparable results were achieved using the values

obtained by laboratory testing analysis. In another

study, Arabani and Hamedi [23] evaluated the effect of

liquid antistrip additives on moisture damage of HMA

with thermodynamic and laboratory concepts. Khodaii

et al. [24] evaluated the effect of a liquid antistrip agent.

The results of this research demonstrated that liquid

antistrip agent decreases the difference between the

free energy of the adhesion of aggregate–asphalt binder

in dry and wet conditions and this difference is equal to

the amount of energy released when stripping occurs.

Therefore, coating of the aggregate surface with liquid

antistrip causes the mixture to be more resistant to

moisture damage. Nejad et al. [25] employed the SFE

method to evaluate the role of hydrate lime on moisture

damage of HMA. The results of their study showed that

the use of hydrated lime decreases the acid SFE and

increases the base SFE of the two types of aggregates

employed in their study. These changes lead to the

promotion of adhesion between asphalt binder and

aggregate in the absence and presence of water,

especially in the mixtures containing acidic aggregates

prone to moisture damage.

Even though there are many researches in the field

of employing antistrip agents in HMA, there are few

studies which have evaluated the effect of nanoparti-

cles on the moisture damage of HMA.

1.2 The statement and objectives of the present

study

The SFE concept, which reflects the physical–

chemical surface characteristics of asphalt and

aggregate material, has strong potential applications

in asphalt mixture design and analysis. In this study,

the mechanism of the effect of nano ZnO on the

resistance of asphalt mixtures against moisture

damage has been investigated along with applying

thermodynamic concepts. The ITS test has been

carried out by applying an unconfined compressive

load to the samples in a controlled strain mode in dry

and wet conditions according to the AASHTO T283

test to prove the SFE results.

The main objectives of this study are:

• Determining SFE components of nano ZnO-

treated and untreated asphalt binder;

• Studying the effects of nano ZnO on moisture

damage of HMA; and

• Comparing the results of nano ZnO treatment by

laboratory tests and SFE method.

2 Materials

2.1 Aggregate

This research included two types of aggregate, lime-

stone and granite, from two different mines, namely

Makadam and Ghiam Dasht of Tehran city. The

limestone and granite aggregates represent a consid-

erable difference in range in mineralogy and in degree

of associated stripping. The chemical composition of

limestone and granite aggregate used in this study is

listed in Table 1. The gradation of the aggregate (mid

limits of ASTM specifications for dense aggregate

gradation) is presented in Table 2. The nominal size of

this gradation was 12.50 mm. The physical properties

of the aggregates are presented in Table 3.

Table 1 Chemical composition of the two types of aggregates

Properties Limestone Granite

pH 8.8 7.1

Silicon dioxide, SiO2 (%) 3.8 68.1

R2O3 (Al2O3 ? Fe2O3) (%) 18 16.2

Aluminum oxide, Al2O3 (%) 1 14.8

Ferric oxide, Fe2O3 (%) 0.4 1.4

Magnesium oxide, MgO (%) 1.2 0.8

Calcium oxide, CaO (%) 51.3 2.4

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2.2 Asphalt binder

In this experimental research, a pure asphalt binder of

60/70 penetration grade from the Isfahan mineral oil

refinery was employed. To characterize the properties

of the base and modified asphalt binders, conventional

test methods, such as the penetration test, softening

point test, and ductility were applied. The engineering

properties of the asphalt binder are presented in Table 4.

The tests conducted on the asphalt binder samples have

been repeated 3 times on separate samples.1

2.3 Nano ZnO

Nano-sized particles have been employed in numerous

applications to improve the properties of different

materials [26]. Nanotechnology and its fast progress in

different civil engineering fields have created new

changes in the pavement industry [27]. The prepared

nanoparticles with new properties would result in

unknown effects on asphalt binder performance of an

asphalt mix [28]. An asphalt mix is composed of

macro, micro and nano parts [29, 30]. Aggregates,

fillers and the asphalt binder and its components are

considered macro, micro and nano parts of asphalt,

respectively [31].

The aim of this study is investigating the moisture

damage of the asphalt mix after adding nano ZnO

particles to the asphalt binder. Actually, nano ZnO is

used as an antistrip additive in this study. Zinc oxide is

an inorganic compound with ZnO formula and is

assigned discrete CAS registry numbers 1314-13-2.

Nano ZnO is a white powder, insoluble in water, and

widely used as an additive in numerous materials and

products including rubbers, plastics, ceramics, glass,

cement, and lubricants [32]. Physical properties of

nano ZnO are given in Table 5.

According to the previous study [33–35], it has

been observed that the dosage of nanomaterial

additives is normally between 1 % and 8 % by the

weight of asphalt binders. The percentages used in

the study were 2 and 4 percent by the weight of

asphalt binder.

3 Experimental set up and procedure

The following tests were conducted on each sample

in three duplicates. For each mixture of aggregate

and asphalt binder, at least three separate samples

were produced to find out the reproducibility of the

results.

Table 2 Gradation of the aggregates used in the study

Sieve (mm) 19 12.5 4.75 2.36 0.3 0.075

Lower–upper limits 100 90–100 44–74 28–58 5–21 2–10

Passing (%) 100 95 59 43 13 6

Table 3 Physical

properties of the aggregateTest Standard Limestone Granite Specification

Specific gravity (coarse agg.) ASTM C 127

Bulk 2.612 2.654 –

Saturated-surface-dry 2.643 2.667 –

Apparent 2.659 2.692 –

Specific gravity (fine agg.) ASTM C 128

Bulk 2.618 2.659 –

Saturated-surface-dry 2.633 2.661 –

Apparent 2.651 2.688 –

Specific gravity (filler) ASTM D854 2.640 2.656 –

Los Angeles abrasion (%) ASTM C 131 25.6 19 Max 45

Flat and elongated particles (%) ASTM D 4791 9.2 6.5 Max 10

Sodium sulfate soundness (%) ASTM C 88 2.56 1.5 Max 10–20

Fine aggregate angularity ASTM C 1252 46.65 56.3 Min 40

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3.1 Preparation method of the modified asphalt

binder with nano ZnO

To formulate the modified asphalt binder, 2 and 4

determined percentages of nano ZnO by weight of

asphalt binder were added to the base asphalt binder

produced in Isfahan refinery. Since a homogenous

distribution of the nano particles was significantly

important, a ‘‘nano particle distributor’’ device with

high rotation rate and a temperature control chamber

was employed. The asphalt binder was mixed with the

nano ZnO for 4–5 min at 130–140 �C and 14,000 rpm

in a batch with 15 cm diameter and 30 cm height.

Then, the prepared asphalt binder was used in

preparing the asphalt binder samples.

3.2 Mix design

The optimum asphalt binder content for the mix design

was determined through taking the average values of

the following three asphalt binder contents:

1. Binder content corresponding to maximum stability;

2. Binder content corresponding to maximum bulk

specific gravity; and

3. Binder content corresponding to the median of

designed limits of air void percent in the total

mix.

The stability value, flow value, and voids filled with

asphalt binder are checked with the Marshall mix

design specification [36].

It is noteworthy that the mix design was performed

with the aggregates without any antistrip additives

(nano ZnO).

3.3 Tensile strength ratio (TSR)

By the cohesive strength of the asphalt binder and the

bond strength at the asphalt binder–aggregate inter-

face, ITS of a HMA is generated. From the maximum

load that the sample can undergo prior to cracking, the

ITS is calculated [37]. Consequently, any additives in

the dry and moisture-conditioned stages that could

generate a higher ITS in the HMA mix, will improve

the long-term performance of an HMA pavement. This

test includes loading a cylindrical specimen with

vertical compressive loads, which creates a relatively

uniform tensile stress along the vertical diametrical

plane. Failure normally occurs in the form of splitting

along this loaded plane [8].

From each mix (dry and wet), six samples were

prepared and compacted. The compacted specimens

should possess air void contents between 6.5 and

7.5 %. Half of the compacted specimens are condi-

tioned. First, to a level between 55 and 80 %,

vacuum is applied to partially saturate specimens.

Vacuum-saturated samples are reserved in a freeze

cycle (-18 �C for 16 h) and then a thaw cycle

(60 �C water bath for 24 h). After this period the

specimens are regarded as conditioned. The other

three samples remain unconditioned at 25 �C. The

failure load for each sample was recorded at 25 �C

(Fig. 1).

Table 4 Results of the experiments conducted on the base and modified asphalt binders

Asphalt binder Penetration grade,

(mm/10)

Softening

point, (�C)

Viscosity, mPas Ductility,

(cm)

Flash point,

(�C)115 �C 135 �C 150 �C

Base asphalt binder 69 47 0.776 0.289 0.156 112 313

Modified asphalt binders

2 % nano ZnO 65 52 0.897 0.331 0.179 [150 321

4 % nano ZnO 63 51 0.960 0.334 0.179 115 323

Table 5 Physical properties of nano ZnO

Properties Nano ZnO

Crystal structure Zinc blend

Shape of particle Cubic

Density (g/cm3) 5.5–5.6

Refractive index 2

BET specific surface area (m2/g) 40 ± 5

Average grain size (nm) &20

Bulk density (g/cm3) 0.28–0.48

pH 8.5–9.5

Water (%) B0.7

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Using the following equation, ITS for each sample

was calculated:

ITS ¼ 2F=tpd ð1Þ

where ITS is the indirect tensile strength (kPa), F is the

failure load (kN), t is the sample thickness (m), and d is

the sample diameter (m).

TSR was determined by the following equation:

TSR ¼ ITScond=ITSuncond

� �� 100 ð2Þ

where ITScond is the average of ITS of the wet

specimens, and ITSuncond is the average of ITS of the

dry specimens.

3.4 SFE measurement

The surface energy of the asphalt binder was quanti-

fied in this study using Wilhelmy plate (WP) estab-

lished by Hefer et al. [38].

According to the Young–Dupre’ equation, Van Oss

et al. [39] suggested the following equation:

�DGaL;S ¼ Wa

L;S ¼ DGTotalL; ð1þ cos hÞ

¼ 2 CLWS CLW

L

� �0:5þ CþS C�L� �0:5þ C�S CþL

� �0:5h i

ð3Þ

where DGaL;S is the Gibbs free energy of adhesion,

DWaL;S is work of adhesion, h is contact angle of a

probe liquid (L), in contact with a solid (S), and other

parameters are surface energy characteristics of both

the liquid and solid.

Equation 3 is the fundamental equation employed

to calculate SFE components of the asphalt binder by

quantifying contact angles. In this equation, the solid

(S) is replaced by the asphalt binder under consid-

eration and the liquid (L) is any probe liquid, in this

context defined as a liquid with known SFE charac-

teristics. Equation 3 can be rewritten as follows, if the

square roots of the three unknown surface energy

components of the asphalt binder are represented as x1,

x2, and x3:

CTotalL ð1þ cos hÞ ¼ 2 CLW

S

� �0:5� x1 þ CþS� �0:5� x2

h

þ C�S� �0:5� x3

i

ð4Þ

The measured contact angle of a probe liquid with

asphalt binder and surface energy components of the

probe liquid are substituted into Eq. 4 to create a linear

equation with unknown x1 - x3.

In 1863, to measure the contact angle between a

liquid, Wilhelmy first suggested an indirect measure-

ment method, whereby a plate is immersed into a

liquid. This is a quasi-static contact angle measure-

ment technique, since the plate is in motion throughout

the process (moving at a few microns per second).

From simple force equilibrium considerations, the

difference between the weight of a plate measured in

air and partially submerged in a probe liquid (DF) is

indicated in terms of buoyancy of the liquid, liquid

surface energy, contact angle, and the geometry of the

plate. Therefore, the contact angle between the liquid

and surface of the plate can be calculated from this

equilibrium, as shown in Eq. 5.

cos h ¼ DF þ VimðqL � qair � gÞPtCtotal

L

ð5Þ

where Pt is perimeter of the asphalt binder coated

plate, CtotalL is total surface energy of the liquid, h is the

dynamic contact angle between the asphalt binder and

the liquid, Vim is the volume immersed in the liquid, qL

is the density of liquid, qair is air density, and g is local

gravitational force.

In Eq. 4, there are three unknowns for the asphalt

semi-solid: CLWS , C�S , CþS . These unknowns are the

three components of asphalt SFE: Lifshitz-van der

Waals, Lewis base, and Lewis acid, respectively. To

solve these parameters, at least three solvent liquids,

whose surface energies are known, must be employed

to produce three simultaneous equations. Water,

glycerin and formamide were used here as liquid

solvents because of their relatively large SFE,Fig. 1 Components of the ITS test for a HMA sample

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immiscibility with asphalt binder, and differing SFE

components.

4 Results and discussion

4.1 Results and discussion of the mix design

The optimum asphalt content was found to be 5.6 and

5.1 %, respectively, in control samples made with

limestone and granite aggregates. In addition, the

above asphalt binder quantities were used in all

mixtures, so that the amount of asphalt binder would

not influence the analysis of the test data.

4.2 Results and discussion of the AASHTO T283

test

Figure 2 shows the unconditioned and moisture

conditioned ITS of the HMA mixtures for two types

of aggregates. At the end of the loading test, it was

seen that the ITS values of the wet mixes are lower in

comparison with the ones for dry mixes. This was

anticipated because the decrease in ITS could be

assigned to the loss of adhesion of the mixture and/or

cohesion of the asphalt binder. The use of the modified

asphalt binder (asphalt binder with nano ZnO) led to

less decline in adhesion between asphalt and aggregate

than the mixture containing unmodified asphalt

binder. As shown in Fig. 2, the effect of nano ZnO

was higher for improving the adhesion of asphalt–

aggregate in wet conditions.

Figure 3 represented the unconditioned and moist-

ure conditioned TSR properties of the HMA mixtures

for two types of aggregates. The data show that the

unconditioned and conditioned ITS values are notably

improved with the addition of nano ZnO for both types

of aggregates.

TSR of the control mixtures (without nano ZnO)

containing limestone is greater than control mixtures

containing granite, which leads to better resistance

against moisture damage. Considering that limestone

has less SiO2 compared to granite, this causes a

reduction in the bond between asphalt and aggregate.

Thus, using nano ZnO is more effective in mixtures

containing granite aggregate.

Most aggregates possess electrically charged sur-

faces (polar surfaces). This means that aggregates

have high polar SFE component. Asphalt binder,

which is mainly composed of high molecular weight

hydrocarbons, shows little polar activity. As a result,

the bond that is established between asphalt and an

0

200

400

600

800

1000

1200

1400

1600

0% nano 2% nano 4% nano

Indi

rect

Ten

sile

Str

engt

h (k

Pa)

Types of asphalt binder

Conditioned with granite aggregate Unconditioned with granite aggregate

Conditioned with limestone aggregate Unconditioned with limestone aggregate

Fig. 2 Unconditioned and

conditioned ITS in samples

containing limestone and

granite aggregate

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aggregate is primarily due to relatively weak disper-

sion forces. Nano ZnO treatment decreases the asphalt

binder acidity. This causes the increase of adhesion

between asphalt binder and acidic aggregate such as

granite.

4.3 Results and discussion of the SFE of asphalt

binder

The SFE components of the asphalt binder were

determined using the Wilhelmy Plate method.

Asphalts that possess too much non-polar material,

or asphalts in which the non-polar materials are too

low in molecular weight, will be subject to fatigue

cracking in thick pavements, moisture sensitivity, and

rutting [22]. An asphalt binder is acidic in nature. The

acid and base components of AC 60–70 were 2.58 and

0.47 ergs/cm2, respectively. The surface chemistry of

Lewis acids and bases in the case of an acidic

aggregate and an acidic asphalt binder, does not

favour adhesion, and a good bond between an acidic

aggregate and an acidic asphalt binder is difficult to

obtain.

In this study, nano ZnO was employed and added to

the asphalt binder in two different percentages. The

first group of asphalt binder used in this study is the

AC 60–70 binder. The second group of specimens

used the AC 60–70 asphalt binder that was modified

with 2 and 4 % nano ZnO.

The total SFE and its components for the asphalt

binder with and without nano ZnO treatment obtained

in this study, is shown in Table 6.

Comparisons of the results show that adding nano

ZnO increases the total SFE of the asphalt binder, and

from the results it is clear that increasing the

percentage of additive causes the total SFE to increase.

As is clear from the data in Table 6, the SFE of the

asphalt binder without additives was 15.89 ergs/cm2.

The SFE values for the asphalt binder treated with 2

and 4 % nano ZnO were 18.22 and 19.38 ergs/cm2,

respectively.

Most aggregates possess electrically charged sur-

faces (polar surfaces). The asphalt binder, chiefly

composed of high molecular weight hydrocarbons,

exhibits little polar activity; and as a result, the bond

that is established between asphalt and the aggregate is

primarily due to relatively weak dispersion forces

[40]. As seen in Table 6, nano ZnO causes the increase

of non-polar SFE of the asphalt binder.

Table 6 shows that the acid SFE of the asphalt

binder decreased significantly, while the base SFE

increased. The values of the acid SFE in the asphalt

binder treated with 2 and 4 % nano ZnO were 1.93 and

1.67 ergs/cm2, respectively. In addition, the values of

50

55

60

65

70

75

80

85

90

95

100

0% nano 2% nano 4% nano

Ten

sile

Str

engt

h R

atio

(%)

Types of asphalt binder

TSR with granite aggregate TSR with limestone aggregate

Fig. 3 Unconditioned and

conditioned TSR values of

samples containing

limestone and granite

aggregate

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the base SFE in the asphalt binder treated with 2 and

4 % nano ZnO were 0.52 and 0.67 ergs/cm2,

respectively.

Table 6 shows that the acid–base component of

SFE of the asphalt binder without nano ZnO

(2.20 ergs/cm2) is greater than that of the asphalt

binder with nano ZnO in all percentages.

The results of research of Arabani and Hamedi [23]

showed that adding liquid anti stripping causes the

total SFE of the asphalt binder to increase, which

results in a decrease in stripping between the aggregate

and asphalt binder in the presence of water. In another

study [41], it shown that sasobit and asphamin reduced

the total SFE of asphalt binders, whereby the effect of

asphamin in reduction SFE of asphalt binders was

lower.

5 Conclusion

This study assessed the effects of nano ZnO additive

on the susceptibility of HMA to moisture damage by

realizing the mechanisms that affect the adhesive bond

between aggregates, the asphalt binder, the cohesion

free energy of aggregates and the asphalt binder. To

validate the application of surface energy measure-

ments, a performance test was employed.

The following conclusions can be drawn from the

present study:

• Nano ZnO treatment decreased the asphalt bin-

der’s acidity, which has a positive effect on the

adhesion between asphalt binder and acidic

aggregate such as granite.

• Use of nano ZnO in the asphalt binder led to less

reduction of adhesion between asphalt and

aggregate compared to the mixture containing

unmodified asphalt binder.

• The effect of nano ZnO on improving the adhesion

of asphalt–aggregate in wet conditions was higher.

• By adding ZnO to asphalt binder, the uncondi-

tioned and conditioned ITS values were signifi-

cantly improved.

• Samples containing limestone aggregate had better

resistance against moisture damage in comparison

with samples containing granite aggregate.

• By using nano ZnO, the acid SFE component of

the asphalt binder decreased significantly, while

the base SFE increased.

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