This study investigated the behavior of hot mix asphalt (HMA) containing steel slag aggregate (SHMA) compared to HMA containing granite aggregate (GHMA). SHMA showed higher strains than GHMA when exposed to temperature changes, except at void fractions over 4.5%. SHMA also demonstrated improvements in rut resistance, tensile strength, and toughness compared to GHMA. The dynamic modulus of SHMA was higher than GHMA at all temperatures tested. Properly treated SHMA can significantly improve HMA performance.

1. Characteristics of hot mix asphalt containing steel slag aggregate
according to temperature and void percentage
Kyungnam Kim a
, Shin Haeng Jo a
, Nakseok Kim a
, Hyunwook Kim b,⇑
a
Dept. of Civil Engineering, Kyonggi University, 154-42, Gwanggyosan-ro, Yeongtong-gu, Suwon-si, Gyeonggi-do, Republic of Korea
b
Civil Engineering Division, R&D Center, POSCO E&C, 241, Incheon Tower-daero, Yeonsu-gu, Incheon, Republic of Korea
h i g h l i g h t s
SHMA demonstrated higher strains than GHMA except at void fractions 4.5%.
SHMA showed improvement in rut resistance, tensile strength, and toughness.
Dynamic modulus of SHMA was higher than that of GHMA for all temperatures.
SHMA can significantly improve performance when appropriately treated.
a r t i c l e i n f o
Article history:
Received 9 March 2018
Received in revised form 13 August 2018
Accepted 26 August 2018
Keywords:
Steel slag
Hot mix asphalt
Temperature
Air void
a b s t r a c t
This study investigated the behavior of hot mix asphalt mixture containing steel slag aggregate (SHMA).
Compared to hot mix asphalt mixture containing granite aggregate (GHMA), SHMA increased strains by
approximately 15%; however, a void percentage of 4.2% or higher resulted in a strain similar to that of
GHMA. Furthermore, the dynamic modulus of SHMA remained higher than that of GHMA because
SHMA exhibited favorable aggregate interlock due to its high strength and grain shape. In addition, when
the target air void was increased to 4.5%, SHMA showed improvements in rut resistance, tensile strength,
and toughness of 121, 110, and 114%, respectively, compared to GHMA.
Ó 2018 Elsevier Ltd. All rights reserved.
1. Introduction
Limited natural aggregate resources are increasingly unable to
satisfy demand, particularly under evolving environmental regula-
tions. Therefore, various attempts to utilize recycled aggregate or
industrial by-products are being made to facilitate efficient use
of resources and protect the environment [1–5].
Steel slag is an industrial by-product generated from steel mills
that contains free CaO and thus may expand and cause environ-
mental problems. For this reason, steel slag requires aging in
open-air storage for a certain time and under specific vapor and
moisture conditions [6]. If the aging process does not solve the
problem of potential expansion, steel slag could cause harmful
effects on pavement performance, such as deformation, cracking,
and flushing [7,8]. Coomarasamy and Walzak [9] showed that the
expanded portion of SSA pavement contained cracks, and calcium
deposits were generated in the cracks. The Ministry of Transporta-
tion of Ontario investigated pavements constructed using SSA in
the 1970s and found that grey veining appeared around cracks,
and flushing and moisture generated lime [7]. As reported in Ref.
[8], SSA may cause hydration during HMA manufacturing, which
can result in cracks and protrusions in some parts of road surface.
In addition, the potential expansion of SSA containing free lime and
magnesia could generate cracks in pavement [10].
However, if the expansion problem is resolved by sufficient
aging, SHMA pavement shows improved performance. As the SSA
mixing ratio increases, SHMA pavement exhibits increased
dynamic modulus and tensile strength, decreased deformation,
and improved moisture and rutting resistance [11,12,13–16].
Ahmedzade and Sengoz [17] applied SSA to the pavement of an air-
field, and in comparison with conventional pavement, the SSA
pavement showed improved performance. According to a survey
https://doi.org/10.1016/j.conbuildmat.2018.08.172
0950-0618/Ó 2018 Elsevier Ltd. All rights reserved.
Abbreviations: GHMA, hot mix asphalt containing granite aggregate; HMA, hot
mix asphalt; SHMA, hot mix asphalt containing steel slag aggregate; SSA, steel slag
aggregate.
⇑ Corresponding author.
E-mail addresses: nskim1@kgu.ac.kr (N. Kim), hyunwook.kim2@gmail.com
(H. Kim).
Construction and Building Materials 188 (2018) 1128–1136
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2. by Oregon Department of Transportation, sections to which SSA
was applied maintained their initial roughness for five years [18].
In another study, SHMA pavements showed improved rutting
resistance and crack resistance and also maintained the same per-
formance for two years [19]. Wen et al. [20] reported that SHMA
pavement did not require maintenance for 16 years. Kehagia [21]
and Asi [22] showed that SSA improved skid resistance because
of its high strength and irregular aggregate shape. Furthermore,
SSA pavement rarely ravels in regions where studded tires are
widely used in winter [23]. In the northwestern United States,
SHMA is recommended to improve the durability and resistance
of pavement to studded tires [20].
Therefore, SHMA can significantly improve performance, when
appropriately treated. In this study, the wet expansion of SSA
and the characteristics of SHMA pavement were analyzed by mea-
suring the strain responses to changes in moisture and tempera-
ture. SHMA characteristics according to air void percentage were
also analyzed, and the performance of SHMA in terms of the
dynamic modulus, rut resistance, and crack resistance was evalu-
ated. This analysis will contribute to increasing available aggregate
and creating high value resources from industrial by-products.
2. Applicability of steel slag as HMA aggregate
SSA’s potential expansion and other characteristics, which dis-
tinguish SSA from natural aggregate, may be problematic when
used in HMA. Therefore, this section describes the behaviors of
SHMA concrete.
2.1. Material
The SSA used in this study was produced by a steel mill in
Gwangyang, Korea. Basic property tests were conducted, and an
environmental evaluation was performed. As is clear from Tables
1 and 2, the test results satisfied all the Korean standard criteria
[24]. Harmful substances leached out from the SSA did not exceed
the Korean standard. In particular, to examine the wet expansion of
SSA, which is its most problematic feature in this application, an
expansion test in 80 °C water was conducted for 10 days, and the
expansion rate was measured to be 0%. Therefore, the aged SSA
was found to be adequate for use in HMA. The asphalt binder used
in the experiment was PG 76-22, as shown in Table 3.
2.2. Mix design
The SHMA mix design complied with the combined gradations
of 10-mm dense-graded aggregate. The formulation design was
performed according to the combined gradation criterion pre-
sented in Table 4. The test specimens were prepared by a com-
paction method, which involved the application of 50 impacts on
each side of the specimen, using a Marshall hammer. Mixing
design was carried out according to the synthetic granularity crite-
rion in Table 4, and specimens were prepared by compaction 50
times on both sides. Table 5 shows the mix design. Density and sta-
bility were increased 1.21 times and 1.84 times, respectively, using
the SSA The optimum asphalt content for SHMA was 6.1%, which
was 0.5% lower than GHMA with the same grading.
Table 1
Fundamental properties of steel slag.
Item Unit Method Specification Steel Slag Granite
Specific Gravities Bulk Dry g/cm3
AASHTO T 85 2.45 3.310 2.639
Bulk SSD g/cm3
2.5 3.370 2.650
Absorption % 3.0/3.5 1.68 0.46
Soundness (Na2SO2): 5 times % AASHTO T 104 12 2.7 3.5
LA Abrasion % AASHTO T 96 35 20.1 10.3
Flat and Elongated (3:1) % ASTM D 4791 30 12.1 7.6
Immersion Expansion % JIS A 5015 2.0 0.0 0.0
Table 2
Steel slag environmental evaluation [24].
Item Specification Result
Pb 3 mg/L 0
Cu 3 mg/L 0.015
As 1.5 mg/L 0
Cd 3 mg/L 0
Hg 0.005 mg/L 0
Organophosphorus compound 1 mg/L 0
Tetrachloroethylene (PCE) 0.1 mg/L 0
Trichloroethylene (TCE) 0.3 mg/L 0
CN 1 mg/L 0
Cr+6 1.5 mg/L 0
Oil 5% 0.1
Table 3
Asphalt binder parameters.
Test item Method Specification Result
Original Binder
Flash Point Temp., °C AASHTO T 48 230 342
Viscosity, Pas (@135 °C) AASHTO T 316 3.0 1.5
Dynamic Shear (G*
/Sin d), kPa (@10 rad/s, 76 °C) AASHTO T 315 1.0 1.28
Rolling Thin Film Oven Residue (AASHTO T 240)
Mass Change, % – 1.00 0.03
Dynamic Shear (G*
/Sin d), kPa (@10 rad/s, 76 °C) AASHTO T 315 2.20 2.22
Pressure Aging Vessel Residue (AASHTO R 28)
Dynamic Shear (G*
/Sin d), kPa (@10 rad/s, 76 °C) AASHTO T 315 5000 868
Creep Stiffness (@60 s, 12 °C) S, MPa AASHTO T 313 300 98
m-Value 0.300 0.32
K. Kim et al. / Construction and Building Materials 188 (2018) 1128–1136 1129

3. 2.3. Evaluation of contraction and expansion characteristics of SHMA
pavement
In Korea, granite aggregate is mainly used for HMA. SSA and
granite aggregate may have different characteristics because of
the former’s iron content, chemical components, and high density.
To identify these differences, the contraction and expansion char-
acteristics of SHMA were analyzed. In the experiment, to evaluate
the shrinkage expansion characteristics, a specimen was prepared
with a thickness, width, and length of 50, 50, and 180 mm, respec-
tively. The specimen is shown in Fig. 1.
2.3.1. Evaluation of contraction and expansion due to temperature and
moisture
The strains of SHMA and GHMA specimens immersed in water
were measured to examine changes in their length due to temper-
ature and moisture. This experiment was conducted in accordance
with the Test Method for the Immersion Expansion of Steel Slag in
80 °C Water [25]. The specimens were put in a constant-
temperature water bath with a reference temperature of 60 °C,
and then the water temperature was raised to 80 °C, maintained
there for six hours, and then cooled gradually to 20 °C. This was
one cycle, and three cycles were conducted for each specimen.
As shown in Table 6, the SHMA specimen exhibited a larger
strain variation between the highest and lowest temperatures than
the GHMA specimen. The results of measuring the change in strain
according to the temperature change in the soaked test specimen
showed that the strain according to the temperature of SHMA
was 20.1–24.3 le/°C, which was larger than that for GHMA
(15.2–16.2 le/°C). The variation increased with each cycle.
Although the measured strain values were very small, the SHMA
clearly exhibited higher strains than the GHMA. According to the
Pennsylvania Department of Transportation [26], for investigating
a long-term performance of SHMA packaging using SSA aged over a
period of time, the expansion problem of the packaged materials
has not been identified. Thus, further experimentation was per-
formed by changing the conditions in order to analyze the cause
of the variation in the results from the experimental results of this
study.
2.3.2. Evaluation of contraction and expansion due to moisture alone
Because the SHMA specimen showed a high strain of over 30%
under the combined influence of temperature and moisture,
another experiment was performed to investigate the influence
of moisture alone. The specimens were placed in the 20 °C
constant-temperature water bath, and the strain was measured
for 10 days with no temperature change. As shown in Table 7, both
types of specimens showed only minor strains, the values and
trends of which were similar to one another. The measured strains
were very small, and the small increase was attributed moisture
that penetrated the cut surfaces of the specimens, where the aggre-
gate was not covered by the asphalt binder. Because the strain was
found to be very small and both SHMA and GHMA showed similar
strains, SHMA pavement sufficiently aged to prevent expansion
was considered to be free from moisture-related expansion
problems.
Table 4
Grading curve and envelope for 10 mm dense-graded mix [1].
Sieve Size (mm) 13 10 5 2.5 1.2 0.6 0.3 0.15 0.08
Spec. 100 98–100 70–90 40–67 20–45 10–30 10–20 3–14 2–10
Mix (SHMA, GHMA) 100.0 98.0 81.2 58.9 32.0 17.3 10.1 7.1 4.6
Table 5
Mix design.
Blend Asphalt Content (%) Density (g/cm3
) VMA2
(%) Air Void (%) VFA3
(%) Pba (%) Stability (N) Flow (1/10 mm)
Bulk TMD1
SSA 6.1 2.798 2.915 16.6 4.0 80.6 0.18 14,324 30
Granite 6.6 2.315 2.411 16.2 4.0 80.3 0.70 7,765 28
1
TMD: Theoretical maximum density.
2
VMA: Volume of voids in mineral aggregate.
3
VFA: Voids filled with asphalt.
Fig. 1. SSA specimen.
Table 6
Contraction and expansion of specimens immersed in water according to temperature.
Cycle Blend
SHMA GHMA
Strain (le) Strain per unit temp. (le/°C) Strain (le) Strain per unit temp. (le/°C)
80 °C 20 °C 80 °C 20 °C
1 744 489 20.1 582 332 15.2
2 827 539 22.8 501 460 16.0
3 706 750 24.3 370 604 16.2
1130 K. Kim et al. / Construction and Building Materials 188 (2018) 1128–1136

4. 2.3.3. Evaluation of contraction and expansion due to temperature
alone
The strains of SHMA and GHMA specimens were then measured
to investigate their relationship to temperature alone. A tempera-
ture chamber was used to conduct the experiments in a dry condi-
tion, excluding the effect of moisture. Specimens with a strain
gauge attached were placed in the temperature chamber for two
hours at 60 °C and 18 °C, respectively. The strain was measured
when the temperature was stable.
As shown in Table 8, the strain variation in the SHMA specimen
between the highest and lowest temperatures was larger by
approximately 200 le than that in the GHMA specimen. The strain
per unit temperature of the SHMA specimen was larger by approx-
imately 15% than that of the GHMA specimen in Cycle 1; however,
both types of specimens showed an almost similar strain per unit
temperature in Cycle 3. In addition, the SHMA specimen main-
tained a similar strain per unit temperature throughout the cycles,
whereas the GHMA specimen’s strain per unit temperature tended
to increase. Thus, the SHMA was more durable to repeated temper-
ature changes.
Similar to in the case of the deformation rate according to the
temperature change in the soaked state, the strain rate of the
SHMA was larger than that of the GHMA even in the case of the
strain measurement according to the temperature change in air.
The coefficient of thermal expansion of iron is 10–12106
/°C,
which is larger than that of granite (5–10106
/°C). The slag aggre-
gate contains iron components. Because of the characteristics of
the aggregate—the pore shape inside the aggregate is different
from that of natural aggregate—the strain rate of SHMA was higher
than that of the granite aggregate, which is a natural aggregate.
Because the measured strains had very small values, and the
GHMA and SHMA specimens were not drastically different, the
likelihood of thermal cracking was very low. Moreover, no thermal
cracking was observed in studies conducted at actual construction
sites. Nevertheless, if SSA is applied to a region showing a large
daily temperature range, its large expansion at a high temperature
may deteriorate its durability under long-term repetitive tempera-
ture changes, which should be considered for mix design and con-
struction in such regions.
3. Evaluation of SHMA characteristics due to air void percentage
Air voids significantly impact the performance of HMA pave-
ment. In the case of conventional HMA pavement used for surface
layers, the mix design includes an air void range of 3.0–5.0%. In this
study, the SHMA characteristics were analyzed in relation to the air
void percentage to determine its effect on the SHMA behavior.
3.1. Evaluation of contraction and expansion due to air voids
The effect of air voids was considered in this study because it
was assumed that the strain per unit temperature of the SHMA
pavement could be reduced by changes in air void percentage. Tar-
get air void percentages of 3.0, 3.5, 4.0, 4.5, and 5.0% were applied
to the mix design, as shown in Fig. 2, to ensure the same asphalt
film thickness and thus minimize the effect of the asphalt binder.
Table 9 presents the mix design results for steel slag (10-mm
dense-graded mix) according to air void percentage.
The strain per unit temperature in SHMA at which the above
mix designs were applied was measured. Table 10 presents the
measurements, which show that higher air void percentages were
associated with less strain. Furthermore, when the air void was
4.2% or higher, the SHMA strain was similar to that of GHMA.
When the air void was 4.5%, SHMA’s expansion at a high tempera-
ture was decreased and also became similar to that of GHMA. In
addition, when SHMA was applied to a region with a large daily
temperature range, a high target air void of 0.3–0.5% could reduce
the damage due to strain per unit temperature. However, if an air
void is modified by reducing the asphalt content in the mix design,
the asphalt film thickness decreases, which increases vulnerability
Table 7
Contraction and expansion strain of specimens according to moisture alone.
Blend Day
1 2 3 4 5 6 7 8 9 10
Strain of SHMA specimens (le) 18 30 33 33 35 44 46 58 87 118
Strain of GHMA specimens (le) 10 29 33 54 66 73 80 91 121 107
Table 8
Contraction and expansion of specimens according to temperature alone.
Cycle Blend
SHMA GHMA
Strain (le) Strain per unit temp. (le/°C) Strain (le) Strain per unit temp. (le/°C)
60 °C 18 °C 60 °C 18 °C
1 396 824 14.8 311 752 12.9
2 321 900 14.9 252 844 12.8
3 358 1218 15.0 221 1354 14.7
Fig. 2. Gradation chart.
K. Kim et al. / Construction and Building Materials 188 (2018) 1128–1136 1131

5. to cracking and moisture. Therefore, a careful approach is required
to achieve an optimal mix design.
3.2. Dynamic modulus experiment
A dynamic modulus experiment was conducted to evaluate the
characteristics of SHMA by simulating various traffic load condi-
tions, including temperature, weight, and loading rate. In particu-
lar, an analysis of HMA’s viscoelastic property can be utilized for
pavement design [27].
For the dynamic modulus experiment conducted herein, a Euro-
pean Standards Tester from IPC Global, shown in Fig. 3, was used,
following the procedure of AASHTO TP-62 [28]. The experimental
conditions included five temperatures (10, 5, 20, 40, and 54 °C)
and six loading rates (25, 10, 5, 1, 0.5, and 0.1 Hz) for each speci-
men. The specimen had a cylindrical shape with a height of
150 mm and diameter of 100 mm. Linear variable displacement
transducers (LVDT) were installed at 120° intervals, as shown in
Fig. 3, and a load level was determined to ensure micro-strains of
50–75. In general, if the load frequency is high, the dynamic mod-
ulus reflects the rut resistance of asphalt mixtures, and the elastic
behavior of HMA can be evaluated by a phase angle master curve. If
the phase angle is small, the HMA exhibits elastic behavior; if the
phase angle is large, the HMA exhibits low elasticity [29].
The same SHMA that was used in the strain experiment was
used here, with air voids of 3.0, 3.5, 4.0, 4.5, and 5.0%, and a GHMA
specimen with an air void of 4% was adopted for comparison. The
experiment was conducted three times for each specimen. The ref-
erence temperature for the master curves shown in Figs. 4–7 was
5 °C.
As shown in Figs. 4 and 5, the SHMA had a higher dynamic mod-
ulus than GHMA at all load frequencies. In particular, the dynamic
modulus of SHMA was remarkably higher than that of GHMA at a
high temperature, which indicated high rut resistance of SHMA.
Table 9
SHMA mix design according to air void percentage.
Asphalt Content (%) Density (g/cm3
) VMA (%) Air Void (%) VFA (%) Stability (N) Flow (1/10 mm)
Bulk TMD
6.4 2.796 2.882 17.4 3.0 85.3 13,922 27
6.3 2.794 2.895 17.1 3.5 82.7 14,020 27
6.1 2.797 2.915 16.6 4.0 80.6 14,324 29
5.8 2.793 2.925 15.7 4.5 77.7 14,132 29
5.5 2.799 2.946 15.0 5.0 75.0 13,789 28
Table 10
Strain of HMA according to temperature.
Blend Air Voids (%) Strain (le)
60 °C 18 °C Strain per unit temp. (le/°C)
SSA 3.0 232 1192 16.5
3.5 264 1118 16.0
4.0 396 900 14.8
4.5 333 890 14.3
5.0 231 794 13.1
Granite 4.0 311 844 14.6
Fig. 3. Dynamic modulus test. (a) European Standards Tester (IPC Global) and (b) Installed LVDT.
Fig. 4. Dynamic modulus master curves in semi-log scale.
1132 K. Kim et al. / Construction and Building Materials 188 (2018) 1128–1136

6. Table 11 shows the dynamic modulus at the load frequency of
10 Hz. According to Yu and Shen [30], as the air void percentage
increases, the dynamic modulus tends to decrease. The SHMA
showed this tendency. The dynamic modulus differences between
10 °C and 54 °C for the different mixes indicated that as the air
void percentage increased, the difference decreased, which
improved temperature susceptibility. Although SHMA’s dynamic
modulus tended to decrease as the air void percentage increased,
the dynamic modulus of SHMA with an air void percentage of
4.5% was 1.8 times that of GHMA. Therefore, its rutting resistance
remained high despite the increased air voids.
3.3. Rutting resistance
The specimens’ strength against deformation and dynamic sta-
bility were tested in order to evaluate rutting resistance according
to air void percentage. Roy et al. [31] and Li [32] measured the rut-
ting depth of HMA pavement in relation to air void percentage and
showed that, as the air void percentage increased, the rutting
depth also increased, and the pavement became more susceptible
to rutting.
The strength-against-deformation test is a simple test method
used in Korea to evaluate the permanent resistance of asphalt con-
crete. A load is applied to a compacted surface in the same direc-
tion as the loading direction of a wheel so that compaction and
shear cause deformation, such as rutting [33]. Here, HMA speci-
mens were penetrated by a load rod, and the consequential peak
load and vertical deformation were applied to Eq. (1) to calculate
the strength against deformation of the HMA pavement.
SD ¼
0:32P
10 þ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2l l2
p
2
ð1Þ
where
SD: Strength against deformation (MPa)
P: Peak Load (N)
m: Deformation at Peak Load (mm)
The test was conducted in accordance with Annex IV-5 of the
Guidelines for Asphalt Concrete Pavement Construction, provided
by the Ministry of Land, Infrastructure and Transport [34]. Cylin-
drical specimens with diameters of 101.6 mm and heights of
62.5 mm were immersed in 60 °C water for 30 min. As shown in
Fig. 8, a load rod, with a diameter of 40 mm and a lower radius
of 10 mm, was used to apply a vertical load to the center of the
plane.
Table 12 presents the test results, which showed that the
SHMA’s strength was far beyond 4.25 MPa, which is the quality cri-
terion for surface-layer HMA for heavy-traffic roads, as specified by
the Ministry of Land, Infrastructure and Transport [34]. As shown
in Fig. 9, when SSA with an air void percentage of 4.0% was used,
the strength against deformation was approximately 24% higher
than that of GHMA. From the 4.0% air void percentage, the strength
Fig. 5. Dynamic modulus master curves in log-log scale.
Fig. 6. Phase angle master curves.
Fig. 7. Shift factors for dynamic modulus and phase angle master curves.
Table 11
Dynamic modulus at a load frequency of 10 Hz.
Temp. (°C) |E*
|(MPa)
SSA Granite
3.0% 3.5% 4.0% 4.5% 5.0% 4.0%
10 23,047 21,717 20,169 20,608 20,158 19,945
5 14,911 15,118 13,277 13,503 12,955 12,933
20 7620 7890 7261 6902 6677 5411
40 2191 2184 2191 2015 2018 1067
54 800 827 738 692 647 377
K. Kim et al. / Construction and Building Materials 188 (2018) 1128–1136 1133

7. against deformation tended to decrease along with air void per-
centage. Nonetheless, the SHMA’s strength was at least 18% higher
than that of GHMA.
A wheel-tracking test [35] was conducted to evaluate the rut-
ting resistance of SHMA with air void percentages of 4.0, 4.5, and
5.0%. The specimen used in the test was 30 cm wide, 30 cm long,
and 5 cm high. At the test temperature of 60 ± 0.5 °C, a 686-N
wheel load and 628 ± 15-kPa wheel contact pressure were applied.
As shown in Table 13, the dynamic stability of SHMA was 1.6–1.8
times the criterion of 3000 numbers/mm for roads where rutting
resistance is considered an essential property. The SHMA with
the air void percentage of 4.5% exhibited decreased stability by
approximately 2% (200 numbers/mm) compared to the SHMA with
the air void percentage of 4.0%. The rutting resistance due to air
voids showed the same variation as the strength-against-
deformation test. However, the difference was reduced in the
wheel-tracking test. The results of the wheel-tracking test indicate
that even if the air void percentage is increased to 4.5%, the perma-
nent deformation resistance is not significantly affected.
3.4. Evaluation of crack resistance
Crack management is essential because cracks in asphalt con-
crete pavements often lead to irreversible structural and functional
deficiencies that decrease the lifespan of the material and increase
maintenance costs [36]. An indirect tensile strength (IDT) test was
performed according to ASTM D 6931 in order to evaluate the crack
resistance of the SHMA pavement [37]. SSA was expected to
increase crack resistance because aggregate strength can influence
the softening part and the peak load [38]. As shown in Table 14,
when SSA was used, the air voids increased, and thus IDT and
toughness tended to decrease. However, in comparison with gran-
ite aggregate, the IDT and toughness were higher by approximately
4–12% and 6–14% respectively, indicating the SSA’s better crack
resistance. In addition, there was not a significant difference in
the toughness of SHMA specimens with air void percentages of
4.0% and 4.5%.
4. Conclusions
This study analyzed the behaviors of SHMA pavement in com-
parison to GHMA, and the following conclusions were drawn.
1. The strain of SHMA concrete due to water immersion and tem-
perature was evaluated to investigate the problem of SSA’s wet
expansion. The results showed that a sufficient aging treatment
could prevent the wet expansion of SSA. In comparison with
granite aggregate, the strain per unit temperature of SHMA
pavement was slightly higher. As for the HMA strain according
to temperature, SHMA showed a larger expansion at a high
temperature but a smaller expansion at a low temperature,
compared to GHMA.
Fig. 8. Testing for strength against deformation.
Table 12
Results of test on strength against deformation according to air void percentage.
No. Blend Bulk Density
(g/cm3
)
Air Voids (%) Strength Agains
Deformation (MPa)
1 Granite 2.323 4.0 4.71
2 SSA 2.796 3.0 5.92
3 SSA 2.791 3.5 5.96
4 SSA 2.803 4.0 6.01
5 SSA 2.792 4.5 5.74
6 SSA 2.799 5.0 5.57
Fig. 9. Results for test on strength against deformation (SHMA).
Table 13
Wheel-tracking test results.
Blend Air Voids (%) Dynamic Stability (number/mm)
SSA 4.0 5432
4.5 5332
5.0 4987
Table 14
IDT test results.
Blend Air Voids (%) IDT (MPa) Disp. (mm) Toughness (Nmm)
SSA 4.0 1.06 1.34 18,114
4.5 1.04 1.29 18,046
5.0 0.98 1.27 16,724
Granite 4.0 0.94 1.30 15,844
1134 K. Kim et al. / Construction and Building Materials 188 (2018) 1128–1136

8. 2. The dynamic modulus test showed that the dynamic modulus
of SHMA was higher than that of GHMA in every temperature
zone. In particular, at a high temperature, the dynamic modulus
of SHMA was 1.8 times higher, which indicated better rutting
resistance. When the air void percentage increased, the varia-
tion in the dynamic modulus according to temperature
decreased. This result was consistent with the measurements
of strain per unit temperature according to air void percentage.
Therefore, in a region with a large daily temperature range, an
increased air void percentage could resolve the problem of
strain per unit temperature.
3. The rutting resistance of SHMA was 1.24 times that of GHMA,
and the dynamic stability of SHMA was 5432 times/mm, which
is 1.8 times the criterion for road pavement in Korea (3000
times/mm). SHMA also showed better results in the IDT test
conducted to evaluate crack resistance. The SHMA result for
IDT was 1.06 MPa, which was higher than that of GHMA. The
toughness of SHMA was 18.114 Nmm, which was a 14%
increase. The use of SSA improved both rutting resistance and
crack resistance of the HMA pavement.
4. Since SHMA showed higher strains than GHMA, factors influ-
encing the strain were analyzed to identify a method of reduc-
ing strain. However, the actual strain measurements of SHMA
showed an additional 10 mm per 20 m of pavement, approxi-
mately, for the temperature range of 18 °C to 60 °C, which
was considered quite slight.
5. In conclusion, SHMA mix designs with air void percentages
higher by 0.3–0.5% than the existing target air void of 4% could
reduce the strain to a value similar to that of existing pave-
ments, and the experimental results for specimens with these
characteristics showed no performance problems. However,
future research should evaluate the long-term volume expan-
sion through field applications and follow-up laboratory
investigations.
Conflict of interest
The authors declare that they have no conflicts of interest.
Acknowledgment
The authors would like to thank the members of the research
team, MOLIT, and KAIA for their guidance and support throughout
the project.
Funding
This study was supported by the Ministry of Land, Infrastruc-
ture and Transport (MOLIT) and the Korea Agency for Infrastruc-
ture Technology Advancement (KAIA); conducted under the
research project, ‘‘Development of Eco-Friendly Pavements to Min-
imize Greenhouse Gas Emissions”. The finding source has no role in
study design; in the collection, analysis and interpretation of data;
in the writing of the report; and in the decision to submit the arti-
cle for publication.
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