International Journal of Civil Engineering and Technology (IJCIET)
Volume 10, Issue 04, April 2019, pp. 730–737, Article ID: IJCIET_10_04_077
Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJCIET&VType=10&IType=4
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
© IAEME Publication
Scopus Indexed
RELATIONSHIP BETWEEN WORKABILITY
AND MOISTURE-INDUCED DAMAGE OF
ASPHALT CONCRETE MIXTURES
A. K. Arshad, E. Shaffie
Institute for Infrastructure Engineering and Sustainable Management (IIESM),
Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia
W. Hashim, S. M. Khalil
Faculty of Civil Engineering, Universiti Teknologi MARA, 40450 Shah Alam,
Selangor, Malaysia
ABSTRACT
This paper details a laboratory study which aims to understand the relationship
between moisture-induced damage and torque in asphalt concrete mixtures. Research
was conducted using three different gradations of dense asphaltic concrete mixed at
two different temperatures of 140oC and 155oC. Torque readings were measured using
a transducer at different temperatures while compacting the mixtures using a gyratory
compactor and these were logged using a software. Indirect tensile strength tests were
conducted on these samples for both dry and wet conditions to obtain the tensile
strength ratio (TSR). The findings suggest that any increase in the value of torque will
result in the decrease of Tensile Strength Ratio (TSR). This research also found a
significant relationship between torque and TSR; all the variables (TSR, mixing and
compaction temperatures) significantly influenced torque. This implies that any
increase in TSR at different level of mixing and compaction temperatures will
decrease the value of torque. The findings from this research can be used as guidance
on workability for the asphalt industry.
Key words: Workability, Torque, Moisture-Induced Damage, Asphalt Concrete.
Cite this Article: A. K. Arshad, E. Shaffie, W. Hashim, S. M. Khalil, Relationship
Between Workability and Moisture-Induced Damage of Asphalt Concrete Mixtures,
International Journal of Civil Engineering and Technology 10(4), 2019, pp. 730–737.
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1. INTRODUCTION
Workability and moisture-induced damage of asphalt concrete has attracted a significant
interest among scholars. This can be attributed to the importance of workability and good
adhesion due to improved moisture resistance and reduction in risk associated with stripping
in the asphalt concrete mixtures. While a number of researches have been conducted on
workability and moisture induced damage separately across the globe [1-9], little attention has
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Relationship Between Workability and Moisture-Induced Damage of Asphalt Concrete Mixtures
been directed towards the relationship between workability and moisture-induced damage.
Improved workability of asphalt concrete mixtures can lead to better compaction, leading to
improved performance of asphalt concrete. Masad et al [10] emphasized on the need to
develop a method to relate field compaction to laboratory compaction in order to predict
asphalt mixture compactibility. In addition, Ahmad et al [11] expressed concerns on the
current issue of permanent deformation and moisture-induced damage in asphalt concrete for
highways in Malaysia. Literature has also shown that there is a need for improvement of the
workability measurement device and an in-depth study on the influence of workability on the
compaction of asphalt concrete; research in this area would likely result in guidance on the
compaction of a particular mix on the roadway. In addressing the aforementioned research
gap, this paper examines the relationship between workability (in terms of torque) and
moisture-induced damage of asphalt concrete mixture.
Cabrera [12] defines workability of asphalt concrete as "the property which allows the
production, handling, placing, and compaction of a mix with minimum application of
energy”. In other words, a mixture with good workability will require less energy from
production to application. Stripping arising from moisture damage is a known form of
pavement distress which leads to high maintenance costs for all types of roads. A number of
theories [13-16] have been proposed to explain moisture damage in asphalt concrete and most
of these theories relate moisture damage to loss of adhesion resulting from one or more of the
following mechanisms: (a) loss of cohesion (strength) and stiffness of the asphalt film; (b)
failure of the adhesive bond between the aggregate, and asphalt cement (often called
stripping) (c) chemical interactions between asphalt and minerals on the aggregate surface.
In a research which evaluates the stripping resistance of the Malaysian asphalt concrete
using hydrated lime as anti-stripping additive, Esarwa et al [17] observed an increase of
Indirect Tensile Strength of asphalt concrete due to the increase of adhesion bond between the
aggregate and bitumen which tends to increase the stripping resistance. When asphalt cement
come in contact with dust coating, this prevents contact with the aggregate surface and result
in stripping of the asphalt concrete mixture. This kind of stripping due to excessive dust
coating on the aggregate is documented in the literature [18]. This problem can be addressed
by washing the aggregate in the quarry. Previous studies [19] have also demonstrated that
adhesion can be improved when dust-contaminated coarse aggregates are washed.
Yoon et al [20] mentioned that good bonding is improved by rough textured aggregate
surfaces. Texture here refers some of the aggregate physical properties such as surface
roughness, texture, angularity, porosity, aging of the aggregate surface through environmental
effects, coating of adsorbed on the surface of the aggregates, and the nature of dry aggregate
versus wet aggregate affects asphalt and aggregate bond. In the same line of reasoning, Hicks
[21] also stated that moisture damage is influenced by aggregate characteristics. Further, Pan
and White [22] highlighted that stripping resulting from fine aggregate is severe because the
fine aggregate constitutes the basic matrix of the mixture. Stripping can be reduced to the
minimal level by restricting only to coarse aggregates. Johson and Freeman [23] have
mentioned that factors such as inadequate pavement drainage, inadequate compaction,
excessive dust coating on the aggregate, inadequate drying of aggregates, weak and friable
aggregates and the use of waterproofing membranes and seal coats are the problems
associated with stripping.
Empirical research has also shown that stripping occurred in asphalt pavements when the
tensile strength ratio (TSR) of unconditioned samples to conditioned samples is equal to or
below 75% [18, 24, 25]. However, it has been observed that many highway agencies used
minimum TSR value of 80% as the acceptable criteria to evaluate the resistance of asphaltic
mix in terms of moisture damage. Laboratory test procedures using different methods have
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A. K. Arshad, E. Shaffie, W. Hashim, S. M. Khalil
been developed for estimating and predicting the moisture-induced damage in the asphalt
industry [26, 27]. The approach used for this research is based on the ratio of the indirect
tensile strength of condition (wet) specimens to those unconditioned (dry) specimens as
indicator of moisture resistance of the asphaltic mixture. The objective of this study is
investigate the relationship between moisture-induced damage and torque in asphalt concrete
mixtures.
2. MATERIALS AND METHODS
2.1. Materials
This research used locally available granite aggregates provided by the Kajang Rock Quarry
in the state of Selangor, Malaysia. Three different gradations of aggregate for dense asphalt
concrete type AC14 as shown in Table 1 were selected based on the Public Works
Department of Malaysia’s (PWD Malaysia) Specification for Road Works (the upper limit,
mid-point limit and lowest limit of percentage passing). The proportion of coarse and fine
aggregates between upper, mid-point and lower limit is almost similar, as shown in Table 2.
The properties of aggregates complied with the requirements of PWD Malaysia’s
specifications as shown in Table 3. For the different gradations, the combined aggregate
specific gravities of 2.606, 2.607 and 2.608 gm/cm3 were determined respectively.
Table 1 Aggregate Gradation AC14 and OBC used in the research
Mix Designation
20.0 mm
14.0 mm
10.0 mm
5.0 mm
3.35 mm
1.18 mm
425 μm
150 μm
75 μm
Filler (OPC) %
Bitumen Content %
Power ^
0.45
3.85
3.28
2.82
2.06
1.72
1.08
0.68
0.43
0.31
Mid-point
100
95
81
56
47
26
18
10
6
2
4.71
Wearing Course AC 14
Specification Passing Limits
100
90 – 100
76 – 86
50 – 62
40 – 54
18 – 34
12 – 24
6 – 14
4–8
2
4-6
Table 2 Proportion of Coarse and Fine Aggregate
Aggregate combination
Coarse
Fine
Highest point
%
46
53
Midpoint
%
53
47
Lowest point
%
60
40
Table 3 Properties of Aggregate
Property
Aggregate Abrasion Value AIV %
Aggregate Impact Value, AIV
%
Aggregate Crushing Value, ACV
%
Water absorption
%
Specific Gravity each grading
gm / cm3
Flakiness Index
%
Test Result
22.6
21.64
22.5
0.65
2.606 2.607
2.608
13
Polish Stone Value , PSV
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48
PWD
Requirements
< 25 %
< 25 %
< 25 %
< 2%
< 25 %
> 40 %
732
Designation
ASTM : C 131-96
BS 812: PART 112:1990
BS 812: PART 110
( BS 812 : PART107:1995)
( BS 812 : PART
107:1995)
( BS 812 : PART 105:
1990)
( BS 812 : PART 114:
1989)
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Relationship Between Workability and Moisture-Induced Damage of Asphalt Concrete Mixtures
This study is in accordance with section 4.3.3.2 (b) of PWD Malaysia’s Specification for
Road Works [30] for flexible pavement and Portland cement is used as mineral filler in the
HMA mixtures to improve adhesion between the aggregate and bitumen. The proportioned
aggregates were mixed with bitumen of 80/100 penetration, with the properties as shown in
Table 4 and having a specific gravity of 1.03 gm/cm3. The asphalt mixtures were prepared to
determine the Optimum Bitumen Content in accordance with ASTM D 1559 using 75
blows/face compaction as per the requirements of the PWD Malaysia’s specification.
Table 4 Properties of bitumen
Type of test
Test result 80/100
Penetration at 25°C, 100g
Softening point (°C)
Ductility at 25°C (cm)
Viscosity at 135 °C (cP)
91
47.5
100
425
Designation
ASTM D 5
ASTM D 36
ASTM D 113
ASTM D 4402-02
2.2. Methodology
The test involves preparation of the asphalt concrete mixture for the three different gradations
stated in the preceding section. Two different mixing temperatures of 140oC and 155oC were
used. The methodology for the research is shown in Figure 1.
First, the mixture was mixed at 140°C, then the temperature was regulated to 135°C and
mixed again; the torque at this temperature was recorded using the torque measuring device as
shown in Figure 2. The mix was then compacted using Superpave gyratory compactor (Figure
3) through the application of a vertical stress 600 kPa via the end platens to the known mass
of asphalt concrete mixture within a 100 mm internal diameter mould, at an angle of 1.25°. At
the same 135 °C, for the compaction process targeted at 7% air voids; the density, shear stress
and gyrations were recorded. The samples were then tested for moisture susceptibility using
the indirect tensile strength in accordance with ASTM D 4867.
The same sample was mixed at 140°C and the temperature was regulated to 120°C. The
torque and energy were recorded and later compacted at the same 120°C to obtain 7% air
voids and density, shear stress and gyrations were recorded. The samples were then tested for
moisture susceptibility using the indirect tensile strength in accordance with ASTM D 4867.
The mix was mixed at temperature of 140°C. The temperature was regulated to compaction
temperature at 105°C and 90°C and same procedures were repeated.
Figure 1 Flow chart for methodology
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A. K. Arshad, E. Shaffie, W. Hashim, S. M. Khalil
Next the mixing temperature was at 155°C then temperature regulated to the compaction
temperature at 150°C and the torque recorded and then compacted at this temperature until it
yielded air voids of 7 percent density. Shear stress, gyrations, was recorded. The samples
were then tested for moisture susceptibility using the indirect tensile strength in accordance
with ASTM D 4867. The process described above was repeated at the compaction
temperatures of 135°C, 120°C, 105°C and 90°C.
Figure 2 Torque device to measure workability
Figure 3 Gyratory compactor and mould
3. RESULT AND DISCUSSION
The results for the torque measurements and TSR values obtained were then analysed.
Pearson Correlation was carried out to examine the relationship between TSR and Torque.
The result found that there was a significant relationship between torque and TSR at r = 0.737, p<0.01. This result revealed the negative relationship between the variables. This
implies that any increase in the value of torque will result to decrease in TSR. Table 5
presents the summary of Pearson Correlation result.
Table 5 Pearson Correlation result between TSR and Torque
Relationship
TSR (Tensile Strength Ratio)
Torque (r)
P-value
-0.737
0.000
Table 6 presents the linear regression analysis in examining the effect of TSR on torque at
different mixing and compaction temperatures. It was found that all the variables (TSR,
Mixing and Compaction temperature) significantly influenced torque at 88.8% (R2=0.888,
F=13.247, p<0.01). This implies that any increase in TSR at different level of mixing and
compaction will decrease value of torque. While this research used asphalt concrete in
examining the relationship between torque and different mixing and compaction temperature
as in Tan et al [28], the findings in this research is consistent with previous studies conducted
by Hurley and Prowell [29] who used warm mix asphalt. The authors examined the
applicability of Sasobit in warm mix asphalt applications including typical paving operations,
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Relationship Between Workability and Moisture-Induced Damage of Asphalt Concrete Mixtures
environmental conditions and high temperature conditions. Consistent with present research,
their finding showed that lower mixing and compaction temperatures can result in incomplete
drying of the aggregate. The resulting water trapped in the coated aggregate may cause
moisture damage. As shown in Table 6, workability (torque) was influenced by TSR at
different mixing and compaction for about 88.8% of the variance.
Table 6 Regression analysis of TSR on Torque
Regression analysis
TSR Tensile Strength Ratio
Mixing temperature
Compaction temperature
R2
F
Sig.
B
-0.052
-0.013
-0.080
t
-0.951
-0.027
-3.707
Sig.
0.385
0.844
0.014
0.888
13.247
0.000
Figure 4 presents the relationship between Torques and Tensile Strength ratio. According
to PWD Malaysia, a value of torque corresponding to 80% TSR is an indication of moistureinduced damage. This graph shows that any value of torque above 17.2 kNm is indicative of
moisture-induced damage. This finding is consistent with previous research [18, 24, 25]. The
authors have stated that moisture damage or stripping occurs in asphalt pavement when the
indirect tensile strength of unconditioned samples to conditioned samples equals below 75%.
This has been demonstrated in a previous work by Tim [30], in which the author used
Hamburg wheel tracking device to predict moisture damage of asphalt concrete. His finding
confirms that when the moisture contained in the aggregate does not completely evaporate
during mixing as a result of low mix temperatures, water may be left in close contact with the
aggregate surface and could lead to increased susceptibility to moisture damage.
Figure 4 Relationship between Torque and TSR
4. CONCLUSIONS
The research has demonstrated that moisture-induced damage can be predicted based on the
value of Torque. Hence, this research has contributed to the body of knowledge on moistureinduced damage as it relates to workability and provides a foundation for more elaborate work
on developing mixture design methodology that can reliably produce asphalt mixtures with
the required performance characteristics. A major limitation of this paper is that the findings
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A. K. Arshad, E. Shaffie, W. Hashim, S. M. Khalil
are based on correlation and regression analyses. Future research should explore other
analytical methods.
ACKNOWLEDGEMENTS
Special thanks to the Research Management Institute (RMI) of Universiti Teknologi MARA
for providing the financial support under the Dana Kecemerlangan fund. The authors would
like to thank the Faculty of Civil Engineering, Universiti Teknologi MARA, Shah Alam,
Malaysia for providing the experimental facilities and to all technicians at Highway and
Traffic Engineering Laboratory.
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