QAAZXCFB

1. Performance Evaluation of Asphalt Concrete Mixes
Containing Granular Volcanic Ash
Jamil A. Naji1
and Ibrahim M. Asi2
Abstract: Granular volcanic ash material is spread over considerable areas of Yemen including urban and suburban areas. Due to the
inferior properties of this material in its natural state, it cannot be used in base and subbase layers. It is common practice, when faced with
such material, to replace it with superior properties filling material. Excavated volcanic ash is disposed off by transporting it to landfill
sites. Such practice is becoming increasingly costly and continuously necessitates allocation of scares and valuable new landfill sites. The
problem in some urban areas is becoming an environmental issue due to the massive buildup of disposed volcanic ash material. The main
objectives of this study are twofold: one to investigate the merits of utilizing waste volcanic ash as a cheap alternative to aggregate for
road construction and consequently this contributes toward an efficient waste management of this undesirable material and reduces its
environmental impact. The effects of using granular volcanic ash material, as a partial replacement of conventional aggregate on the
properties of hot-mix asphalt 共HMA兲, were studied. Four different aggregate replacement proportions were used specifically at 0, 10, 20,
and 30% of total weight of dry aggregate. The 0% volcanic ash content mix was used as the reference mix. Experimental results indicated
that the mechanical properties of all mixes containing volcanic ash aggregate, up to 20%, were within the specification limits of the
Marshall mix design method. In addition, it was found that the use of volcanic ash aggregate improved the HMA creep resistance
properties. HMA with a 10% volcanic ash aggregate replacement gave optimum results in terms of stripping resistance, creep resistance,
fatigue, and resilient modulus.
DOI: 10.1061/共ASCE兲0899-1561共2008兲20:12共754兲
CE Database subject headings: Volcanic ash; Asphalt pavements; Stability; Tensile strength; Creep; Fatigue life; Resilient modulus;
Suburbs; Middle East.
Introduction
Road construction in Yemen has grown at a substantial rate fol-
lowing the reunification of the north and south of the country in
1990. A significant portion of the country’s gross national product
goes to road construction. The average government investment on
rural road building, compared to the total annual investment plan,
has risen from 12.5% in 1997 to more than 23% in 2005. Clearly
a major portion of the state investment goes to road construction.
The country has almost completed the construction of about
8,000 km of two way two lane paved rural roads. A major por-
tion of these roads are arterials connecting the main cities in the
country.
The use of good quality conventional crushed aggregate mate-
rials in road construction is becoming increasingly expensive in
Yemen due to the increasing demand of these materials and the
scarcity of good quality materials. Attempts should be made to
explore the utilization of other sources of materials in the most
effective and economical manner.
Many parts of Yemen, particularly in the Sana’a region, are
covered with natural granular volcanic ash. Many sites of granu-
lar volcanic ash are located in urban and suburban areas. Owing
to its low density, cohesionless nature, a relatively high percent-
age of voids, and other undesirable properties, volcanic ash in its
natural state cannot be used in road base and subbase layers.
Therefore, it is considered to be a waste/undesirable material.
When faced with volcanic ash in construction sites, it is common
practice to dispose of it and replace it with superior filling mate-
rial. The excavated waste ash is transported to landfill sites. Such
a solution is expensive, and the amount of hauled materials in-
creases with time, which consequently necessitates the continuous
allocation of new landfill sites. Due to the massive amount of
such materials, the problem in some urban areas is becoming an
environmental issue. Clearly, a better waste management system
of such materials is needed. One possible way to resolve this
problem is to recycle this waste material by improving its physi-
cal properties and utilizing it in the construction industry.
The gradation of volcanic ash varies depending on its source
location, but in general the maximum aggregate size of the mate-
rial ranges between 12 and 18 mm. Since the volcanic ash con-
tains very little or no fine material, it is cohesionless in nature. So
far this material has not been practically used in engineering ap-
plications. However, if properly designed, the material can be
considered to be one of the alternative sources that can be used in
road construction.
Available literature indicates that the use of volcanic ash in
road construction is very limited, and therefore this study can be
considered as a pioneer study in this field in Yemen. Available
studies indicated that some sort of stabilization procedure for vol-
1
Associate Professor, Civil Engineering Dept., Sana’a Univ., P.O. Box
14166, Sana’a, Yemen 共corresponding author兲. E-mail: Jamil.abdulrabb@
gmail.com
2
Associate Professor, Civil Engineering Dept., Hashemite Univ., P.O.
Box 150459, Zarqa 13115, Jordon. E-mail: asi@hu.edu.jo
Note. Associate Editor: Shin-Che Huang. Discussion open until May
1, 2009. Separate discussions must be submitted for individual papers.
The manuscript for this paper was submitted for review and possible
publication on February 15, 2007; approved on May 7, 2008. This paper
is part of the Journal of Materials in Civil Engineering, Vol. 20, No. 12,
December 1, 2008. ©ASCE, ISSN 0899-1561/2008/12-754–761/$25.00.
754 / JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / DECEMBER 2008

2. canic ash can be implemented so that this material can be used as
base and subbase layers in the flexible pavement structures 共Naji
2002; Naji and Ali 2000兲.
Most of the research was performed to study the effect of
using volcanic aggregate in concrete mixes, especially for produc-
ing lightweight concrete and lightweight masonry units
共Demirdag et al. 2007; Demirdag and Gunduz 2006; Hossain
2006; Alonso et al. 2001兲.
In order to improve the performance of hot-mix asphalt
共HMA兲 to meet the requirements under prevailing conditions, dif-
ferent researchers have used fillers and special types of aggregates
in their studies for that purpose. In a recent study, Asi and Shalabi
共2007兲 investigated the possibility of improving the properties of
asphalt concrete mixes by replacing different portions of the lime-
stone aggregate by basalt. The replacement included total replace-
ment of the limestone by basalt, replacing the coarse aggregate
only, and replacing the fine aggregate only. Results showed that
the optimal mix was the mix that had basalt coarse aggregate and
limestone fine aggregate. Other researchers 共Richardson 1914;
Tunnicliff 1962; Anani and Al-Abdul Wahhab 1982; Kandhal et
al. 1998; Asi and Assa’ad 2005兲 used different types of fillers,
material passing sieve No. 200, in their studies. These include
dust from the crushing and screening of aggregates, lime, Port-
land cement, fly ash, and oil shale ash. Although fillers usually
contribute a small portion 共5–7%兲 of the total aggregate mix, they
have a great effect on the HMA properties. Usually, filers are used
to improve bonding between asphalt cement and aggregate, lower
the optimum asphalt content 共OAC兲, increase the density, and
increase the stability 共Brown et al. 1989兲.
In this paper, the possibility of using volcanic ash material as a
partial replacement of conventional aggregate in HMA was inves-
tigated and results are presented. Since change in mix composi-
tion usually influences mix properties, work was oriented to find
out how the inclusion of volcanic ash will affect properties of
HMA. Therefore, different levels of granular volcanic ash were
used in the study and optimum volcanic ash content was obtained.
Research Objectives
The scope of this research is limited to the following:
1. To study the main characteristics of the available granular
volcanic ash and to review available literature on the subject
of using granular volcanic ash in road construction;
2. To study the effect of utilizing granular volcanic ash, as a
partial substitute of the aggregates, on the behavior of HMA;
and
3. To investigate the merits of utilizing waste volcanic ash as
a cheap alternative of aggregate for road construction and
consequently to contribute towards an efficient waste man-
agement of this undesirable material and reduce its environ-
mental impact.
Materials and Experimental Program
A flowchart describing the different levels of the experimental
program followed is shown in Fig. 1. The experimental work
included one asphalt cement 共AC兲 grade, “60/70 pen” AC, one
crushed basalt stone aggregate source, and one granular volcanic
ash source. Details of the experimental program are given in the
next sections.
Materials Characteristics
Asphalt
In this study, “60/70 pen” AC was used as the binder as it is
widely used in Yemen. Penetration 共ASTM D-5兲, ductility
共ASTM D-113兲, and specific gravity 共ASTM D70-82兲 tests were
performed on the binder and the properties test results obtained
are shown in Table 1. The performance grade of the AC used is
PG 64-16 共ASTM 2003兲.
Aggregate and Filler
Two types of aggregates were used in this study: basalt aggregate,
which is the most available and frequently used type of aggregate
in road construction in Yemen, and granular volcanic ash aggre-
gate. The volcanic ash was used as a partial replacement of the
basalt aggregate. Four different mixes with varying proportions of
volcanic ash were examined. The proportions of volcanic ash as a
percentage of total aggregate dry weight were 0, 10, 20, and 30%.
Two different sizes of volcanic ash particles were used. The first
size was that passing through sieve No. 4 共4.75 mm兲 and retained
on sieve No. 10 共2.0 mm兲 and the second size was that passing
through sieve No. 16 共1.18 mm兲 and retained on No. 50
共0.3 mm兲. These two types were found to form the bulk quantity
of volcanic ash in their natural state and are readily available.
Therefore, the use of these types is expected to be the most eco-
nomical. The gradation of the aggregate used in this study is
shown in Table 2 and the aggregate nominal maximum size
共NMAS兲 is 19.0 mm.
Evaluation Criteria:
o Marshall criteria (e.g. stability, flow, VMA, VFA, …etc)
o Indirect tensile strength,
o Fatigue performance
o Dynamic creep
o Resilient Modulus
Conclusions and Recommendations
Control mix:
(0% granular volcanic
ash)
Mix design (four mix design were performed)
Mixes at 10, 20 and
30% granular volcanic
ash contents
Basic properties of collected materials
Results, Analysis and Discussion
Material’s collection:
o Asphalt cement
o Basalt aggregate (coarse and fine)
o Granular volcanic ash
o Mineral filler
Fig. 1. Followed experimental program
Table 1. Basic Properties of Asphalt Cement Used
Property Value
Penetration 60/70
Specific gravity 1.03
Ductility cm 150.00
JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / DECEMBER 2008 / 755

3. 1. Basalt aggregate. Abrasion loss 共ASTM C535-96兲, impact
value 共BS 812兲, specific gravity, and absorption 共AASHTO
T85兲 tests were conducted on the basalt material and the
results are shown in Table 3.
2. Granular volcanic ash. The granular volcanic ash was sub-
jected to a series of tests to determine its basic properties.
This included: gradation test 共ASTM D421-58兲, specific
gravity 共AASHTO T85兲, resistance to abrasion 共ASTM
C535-96兲, and some other index properties. Also a sample of
the grinded material was subjected to Atterberg limits deter-
mination in accordance with AASHTO T89 and T90. The
classification of the volcanic ash was found to be well graded
gravel 共GW兲 and 共A1-a兲 in accordance with Unified Soil
Classification System 共USCS兲 & AASHTO classification, re-
spectively. A summary of the volcanic ash index properties
and chemical composition is shown in Tables 4 and 5, re-
spectively.
3. Mineral filler. Dust, material passing sieve No. 200, ob-
tained from the crushing and screening of basalt aggregates
was used as mineral filler. The main reason for using this
filler is its abundance availability and its wide use locally.
The physical properties of the filler are included in Table 3.
Experimental Work
Mix Design
Although Marshall mix design is being phased out in favor of
SuperPave even in some developing countries, this research has
utilized the Marshall procedure 共ASTM D1559兲 because of a lack
of relevant testing facilities in Yemen 共namely, Superpave Gyra-
tory Compactor兲.
Four mix designs, with different granular volcanic ash compo-
sition of 0, 10, 20, and 30% of total aggregate weight were used
in this study. The 0% ash content mix design was used as a
reference mix. Seventy five blows on each side of the 4 in. speci-
mens were applied in accordance with the Marshall requirement
for heavy traffic. The mixing and compaction temperatures were
160⫾2 and 145⫾2°C, respectively.
Five AC percentages were used in each mix design. Three
samples 共replicates兲 were prepared at each AC percentage. Pre-
pared samples were subjected to bulk specific gravity and
stability-flow tests. Then the density-voids analysis was per-
formed and results obtained were graphically analyzed.
For each level of volcanic ash content, OAC that produced 4%
air void was obtained and used to determine the corresponding
Marshall stability, flow, voids filled with asphalt 共VFA兲, and voids
in mineral aggregate 共VMA兲. These values were checked to verify
that they were within the specification limits given in the Asphalt
Institute Manual Series MS-2 共Asphalt Institute 1997兲.
Evaluation Criteria
The four mixes, at their optimal asphalt contents, were evaluated
using a number of different tests to predict field performance,
namely, Marshall stability, flow, VFA, and VMA. Al-Kadi 共2002兲
stated that evaluation criteria using conventional evaluation pro-
cedures are not sufficient to provide critical evaluation of paving
mixtures. Therefore, the use of more advanced paving mix tests is
necessary to evaluate important mix characteristics. This includes
Table 2. Aggregate Gradation Used in Study
Sieve
size
共mm兲
Specification limits
共% pass兲
Used gradation
共% pass兲
Lower Upper
25.00 100 100 100.0
19.00 90 100 95.0
12.50 70 90 80.5
9.50 58 78 68.0
4.75 35 55 45.5
2.36 20 40 30.5
1.18 12 33 23.0
0.30 6 16 11.0
0.15 4 12 8.5
0.075 2 8 5.0
Table 3. Basic Properties of Basalt Aggregates and Mineral Filler
Property
Aggregate type
Basalt coarse
aggregate
Basalt fine
aggregate
Mineral
filler
Specific gravity 2.789 2.88 2.965
Absorption 共%兲 4.25 — —
Impact value 共%兲 5.0 — —
Abrasion loss 共Los Angeles兲 共%兲 18.0 — —
Table 4. Volcanic Ash Properties
Property Value
Specific gravity 1.98
Liquid limit NPa
Plasticity index NPa
Organic matters Non
Sulfate content Non
Passing No. 200 sieve 共%兲 0.0
Clay content Non
Unified classification GWb
AASHTO classification A-1-a
Coefficient of uniformity 5.60
Coefficient of curvature 1.15
Wearing percentage 共%兲 27.00
a
NP=nonplastic.
b
Well graded gravel.
Table 5. Chemical Composition of Volcanic Ash
Component
Percentage
共%兲
Silicon dioxide 共SiO2兲 47.20
Titanium dioxide 共TiO2兲 1.70
Aluminum oxide 共Al2O3兲 19.20
Ferric oxide 共Fe2O3兲 11.60
Manganese oxide 共MnO兲 0.80
Magnesium oxide 共MgO兲 4.20
Calcium oxide 共CaO兲 8.10
Sodium oxide 共Na2O兲 4.80
Potassium oxide 共K2O兲 1.20
Phosphorus pent oxide 共P2O5兲 0.50
Lithium oxide 共LiO兲 0.50
Total 99.80
Note: Source: Hosain 共1999兲, reprinted with permission.
756 / JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / DECEMBER 2008

4. water sensitivity, fatigue life, creep resistance, and dynamic
modulus. Thus, the results from these tests were used as addi-
tional evaluation criteria.
For each level of ash content and at its OAC, enough samples
were prepared to study the properties previously mentioned.
Results and discussion
The following sections present the effect of the volcanic ash in-
clusion on the different properties of the HMA.
Effect of Volcanic Ash Content on Optimum Asphalt
Content
The effect of volcanic ash on the OAC needed for the mixture
was studied. Results are presented in Fig. 2. It is clear from the
figure that the OAC increases with increasing volcanic ash con-
tent. This can be attributed to the fact that granular volcanic ash
contains some vesicles 共voids兲 which were created by expansion
of the gas bubbles during the eruption of magma 共USGS 2000兲.
These vesicles tend to store part of the asphalt resulting in more
required asphalt.
Statistical analysis using Statistical Package for Social Science
共SPSS兲 software was performed to study whether or not there are
statistically significant differences between the OAC means, i.e.,
to check if the difference in the OAC values obtained is due to
experimental error or to the inclusion of the volcanic ash. One
way analysis of variance 共ANOVA兲 for the single factor model
was used for this analysis. The appropriate procedure for testing
the differences of treatment means 共␮s兲 is to check the following
hypothesis 共Montgomery 1991兲:
H0: ␮1 = ␮2 = ... ... ... . = ␮n 共1兲
H1: at least two means are not equal 共2兲
For testing the previous hypothesis, ANOVA utilizes the F test
in which the estimate of between groups variance 共SSR兲 is com-
pared with the estimate of within-groups variance 共SSE兲 i.e., F
=SSR/SSE. If the SSR is considerably larger than SSE, then the
value of the F ratio will be higher, which indicates that the dif-
ferences between the means are unlikely to be due to chance
共Bryman and Cramer 1990兲.
The F ratio is considered to be high if its significance level
共SL兲 is less than the selected SL, which is usually selected to be
5%. Thus, the SL should be less than 0.05 in order to achieve a
significant effect of any factor.
Results from ANOVA 共Table 6兲 indicate that OAC means are
significantly different from each other and this difference is due to
the different percentages of volcanic ash.
Effect of Volcanic Ash Content on Stability and Flow
As expected, the inclusion of the granular volcanic ash has influ-
enced the behavior of the asphalt mixes. Fig. 3 shows the rela-
tionship between Marshal stability and volcanic ash content. The
general trend shows that as the ash content increases the stability
slightly decreases. This might be attributed to the porous nature of
volcanic ash, which led to lower strength compared with basalt
aggregate.
Although the stability slightly decreased with increasing ash
content, the stability of mixes at volcanic ash contents up to 20%
were within the limits of Marshall criteria for heavy traffic, i.e.,
above 8 kN 共1,800 lb兲. Statistical analysis using one way
ANOVA was used to check whether or not the differences be-
tween stability means, of the volcanic ash contents studied, are
statistically different. Results from ANOVA revealed that stability
means are significantly different at 5% SL.
The flow property of the mixture, as shown in Fig. 4, increases
slightly with the increase in the amount of volcanic ash, and this
may be due to the increased amount of the asphalt content with
the increase of the ash content. Although the flow increased with
the increase of ash content, the flow at all levels of volcanic ash
contents was also within the limits of Marshall criteria for heavy
traffic, i.e., 2–3.5 mm.
Effect of Volcanic Ash Content on Unit Weight
Fig. 5 illustrates the effect of granular volcanic ash content on
sample unit weight. The densities of the HMA samples containing
0
2
4
6
8
0 10 20 30
Volcanic Ash Content (%)
Optimum
Asphalt
Content
(%)
Fig. 2. Effect of granular volcanic ash content on optimum asphalt
content
Table 6. Analysis of Variance for Optimum Asphalt Content Results Obtained
Source of variation Sum of squares DOF Mean square F Sig. level
Between group 共SSR兲 2.151 3 0.717 224.023 0.000
Within group 共SSE兲 0.026 8 0.003 — —
Total 共SST兲 2.176 11 — — —
0
3
6
9
12
0 10 20 30
Volcanic Ash Content (%)
Stability
(KN)
Fig. 3. Effect of granular volcanic ash content on mixes Marshall
stability
JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / DECEMBER 2008 / 757

5. granular volcanic ash were lower than those made without the
addition of volcanic ash and this is ascribed to the lower specific
gravity of the volcanic ash compared with that of basalt aggre-
gates.
Effect of Volcanic Ash Content on VMA and VFA
Studying VMA is important because it represents the space that is
available to accommodate the effective volume of asphalt and the
volume of air voids necessary in the mixture. Therefore, mini-
mum VMA is necessary to achieve an adequate asphalt film thick-
ness, which results in a durable asphalt pavement. Increasing
density of aggregate gradation to a point where below minimum
VMA values are obtained leads to thin films of asphalt and low
durability mix. Thus, economizing in asphalt content by lowering
VMA is actually counterproductive and detrimental to pavement
quality 共Asphalt Institute 2001兲.
In this study, the effect of volcanic ash addition on VMA per-
centage was evaluated and results are shown in Fig. 6. It can be
seen that VMA increases with the increase in the percentage of
granular volcanic ash content. This effect might be attributed to
the presence of vesicles in volcanic ash particles. These vesicles
tend to increase the VMA in the mixture. All values of VMA
obtained were within the limits of Marshall criteria given in As-
phalt Institute Manual Series MS-2 共Asphalt Institute 1997兲 for
the gradation used, i.e., 19 mm nominal maximum particle size
gradation.
Fig. 7 shows the relationship between the volcanic ash content
and the percentage of VFA. As indicated by the graph, the VFA
decreases with the increase in ash content. The reason for such a
decrease may be attributed to the increase in VMA with volcanic
ash content at a higher rate than that of OAC.
It is important to indicate that all values obtained were within
the specification limits given in the Asphalt Institute Manual Se-
ries MS-2 共Asphalt Institute 1997兲.
Statistical analysis using one way ANOVA indicates that VFA
means are significantly different at 5% SL.
Water Sensitivity Test
„Lottman Test, AASHTO T-283-89…
The resistance to stripping 共water susceptibility兲 of the asphalt
concrete mixes containing granular volcanic ash was evaluated by
measuring the loss of the indirect tensile strength 共ITS兲 after im-
mersion in water for 24 h at 60°C, in accordance with AASHTO
T-283 test procedure. To obtain samples having air voids close to
7% and since no gyratory compactor was available, samples were
compacted by applying 45 blows on each sample side using the
Marshall compactor. The results obtained 共Fig. 8兲 indicate that the
average loss in strength due to water damage was increased by the
increase in the quantity of the granular volcanic ash. Factors that
might have influenced this trend are the relatively high permeabil-
ity of volcanic ash particles and the low unit weight of samples
containing granular volcanic ash compared to control samples.
8
10
12
0 10 20 30
Volcanic Ash Content (%)
Flow
(0.25
mm)
Fig. 4. Effect of granular volcanic ash content on Marshall flow
1
1.5
2
2.5
3
0 10 20 30
Volcanic Ash Content (%)
Unit
Weight
(gm/cm3)
Fig. 5. Effect of granular volcanic ash content on density of mixes
0
10
20
0 10 20 30
Volcanic Ash Content (%)
VMA
(%)
Fig. 6. Effect of granular volcanic ash content on voids in mineral
aggregate 共VMA兲
60
70
80
0 10 20 30
Volcanic Ash Content (%)
VFA
(%)
Fig. 7. Effect of granular volcanic ash content on voids filled with
asphalt
50
60
70
80
90
100
0 10 20 30
Volcanic Ash Content (%)
Tensile
Strength
Ratio
(%)
Fig. 8. Effect of granular volcanic ash content on loss of tensile
strength
758 / JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / DECEMBER 2008

6. The loss in ITS value at 10% volcanic ash content was within
the allowable limit, i.e., 20% loss in ITS 共Cominsky et al. 1994兲.
At percentages higher than 10% volcanic ash content, the loss in
ITS was higher than the allowable limit. Therefore, it is necessary
either to improve the stripping resistance of the mixes containing
more than 10% granular volcanic ash by adding antistripping
agent, like lime or cement, or to limit the granular volcanic ash
content to 10%.
Dynamic Creep
The dynamic creep test is a test that applies a repeated pulsed
uniaxial stress/load to an asphalt specimen and measures the re-
sulting deformations in the same axis using linear variable dis-
placement transformers 共LVDTs兲. A repeated uniaxial load strain
test was performed in accordance with the protocol developed by
the United States, NCHRP 9-19 Superpave models draft test
method W2 -unconfined 共Witczak et al. 2001兲. The applied stress
on the specimens was haversine in shape. The loading pulse rep-
etition of 1,000 ms 共1 s兲 and pulse width of 100 ms 共0.1 s兲 was
selected. The deviator stress during each loading pulse was
69 kPa, and the constant stress that was used to prevent lifting off
the test specimen during the rest period was 11 kPa. The test was
performed at 25°C. The specimen’s skin and core temperatures
during the test were monitored by two thermocouples which were
inserted in a dummy specimen and located near the specimen
under test. The test was continued until the maximum axial strain
limit reached 10,000 ␮strains, or until 10,000 cycles, whichever
occurred first.
Four in. specimens, compacted using the Marshall compactor
at the OAC for each mix, were used in this test. Fig. 9 shows a
typical relationship between the number of load repetitions and
the percentage of accumulated strain for the samples tested at the
different volcanic ash contents 共i.e., 0, 10, 20, and 30%兲. The
figure indicates that as the volcanic ash content increases the ac-
cumulated strain decreases. This suggests that volcanic ash affects
the creep properties of the mixture in a positive manner and this
might be attributed to the rough texture properties of volcanic ash
particles which resulted in an improvement of the interlocking
properties of the aggregate in the mix 共Asi and Shalabi 2007兲.
In addition, creep stiffness analysis indicated that creep stiff-
ness increased with the increase in volcanic ash content. As indi-
cated in Eq. 共3兲, creep stiffness is the ratio between the deviator
stress and the axial accumulated/permanent strain. Creep stiffness
gives an indication of the resistance of the HMA to creep
Eca = ␴d/苸pa
where Eca=axial creep stiffness 共MPa兲; ␴d =deviator stress 共kPa兲;
and 苸pa =axial accumulated/permanent strain 共microstrain or %兲.
One way ANOVA for the single factor model was used for the
analysis of the creep stiffness means. Results indicate that at 5%
SL, creep stiffness means are significantly different from each
other and this difference is due to the variation of the volcanic ash
percentage.
Fatigue Resistance
Fatigue is considered to be one of the significant distress modes in
pavements that are associated with repeated traffic loads. The
fatigue resistance of an asphalt concrete mix is its ability to with-
stand repeated loading without fracture. Fatigue in asphalt con-
crete pavements starts at the bottom of the asphalt concrete layer
and propagates to the surface of the pavement.
In this research, fatigue tests were conducted using universal
hydraulic testing equipment and a haversine loading pulse having
a 0.25 s loading time and 1.25 s rest time. Tests were performed
at 25°C in an environmental chamber where the temperature of
the specimens was maintained within ⫾1°C of the set tempera-
ture. Controlled-stress repeated indirect tensile loading was used
in the fatigue study. For comparison reasons, the applied repeated
loading was varied to create nearly the same initial tensile strain
for all the test samples. Six 4 in.⫻2.5 in. Marshall compacted
cylindrical samples for each volcanic ash content were tested.
Loading was continued until complete failure 共splitting兲 of the
test sample. Fatigue life, which is the number of load repetitions
until failure, was recorded for each sample.
Fig. 10 shows the effect of volcanic ash content on fatigue life.
The figure indicates that fatigue life was improved at 10% addi-
tion of volcanic ash. However, considerable decrease in fatigue
life was noticed at higher volcanic ash contents. The reason be-
hind the increase in fatigue life at 10% volcanic ash content may
be due to the rough surface texture of the granular volcanic ash
particles which resulted in an improvement in the interlocking of
the aggregate. When the percentage of the granular volcanic ash
increased, the lower strength of the granular volcanic ash was
more effective than its rough texture. A previous study, conducted
on basalt and lime aggregate, reported close results 共Asi and
Shalabi 2007兲.
Resilient Modulus Test „MR…
Resilient modulus of HMA is conducted by applying pulsed com-
pressive loads with a haversine waveform. The load is applied
vertically in the vertical diametral plane of the cylindrical speci-
men of the asphalt concrete mix. The resulting total recoverable
diametral deformation 共horizontal兲 is then measured from an axis
90° from the applied force. A resilient Poisson’s ratio is calculated
by dividing the measured recoverable vertical deformation by the
0% Volcanic Ash
0
0.1
0.2
0.3
0.4
0.5
0.6
10 100 1000 10000
No. of load repetitions
Accumulated
Strain
(%)
10% Volcanic Ash
20% Volcanic Ash
30% Volcanic Ash
Fig. 9. Effect of granular volcanic ash content on creep deformation
0
10000
20000
30000
0 10 20 30
Volcanic Ash Content (%)
No.
of
Repetition
to
Failure
Fig. 10. Effect of volcanic ash content on fatigue life
JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / DECEMBER 2008 / 759

7. horizontal deformation. The total resilient modulus is calculated
using the total recoverable deformation which includes both the
instantaneous recoverable and the time-dependent continuing re-
coverable deformation during the unloading and rest period por-
tion of one cycle 共ASTM D-4123兲. The test would usually be used
to gauge the relative performance of HMA for road pavement
design and to evaluate the relative quality of materials 共ASTM
2003兲. The resilient modulus value varies with temperature and
speed/time of loading due to the AC viscoelastic behavior 共Kamal
et al. 2005兲.
In this study, 4 in.⫻2.5 in. cylindrical samples were prepared
at OAC for resilient modulus testing. Eight replicates for each
mix were tested under the diametral resilient modulus 共MR兲 test.
The test was performed by applying a pulse width of 0.1 s and a
pulse repetition of 1.0 s at 25°C test temperature.
The effect of volcanic ash content on resilient modulus values
is presented in Fig. 11. The figure indicates that replacement of
part of the aggregate by granular volcanic ash 共up to 20% ash
content兲 has increased the diametral resilient modulus. However,
the MR value decreased at higher ash contents. The rough surface
texture of the granular volcanic ash particles, which resulted in an
improvement of the interlocking of the aggregate, was the reason
behind the increase in the MR values at the low volcanic ash
contents. At higher volcanic ash contents, the effect of the lower
strength of the granular volcanic ash was more effective than its
rough texture, resulting in a decrease of the MR values.
Statistical analysis was performed to study the significance of
replacing aggregate by volcanic ash in changing the MR values.
ANOVA analysis indicated that there is a significant difference in
the means of the MR values at different volcanic ash contents.
This indicates that the differences in MR values are due to treat-
ments rather than experimental errors.
Conclusions and Recommendations
In this research, the effects of using granular volcanic ash mate-
rial, as a partial replacement of conventional basalt aggregate, on
the properties of HMA were studied. Four different aggregate
replacement proportions were used specifically at 0, 10, 20, and
30% of the total weight of dry aggregate. The effectiveness of the
replacement was judged mainly by the improvements in stripping
resistance, resilient modulus, fatigue life, and creep resistance of
the samples tested. The following can be concluded regarding the
use of granular volcanic ash in HMA:
1. Experimental results proved that partial replacement of basalt
aggregates by granular volcanic ash is technically feasible;
2. The use of volcanic ash in road construction will serve two
purposes: one to reduce the construction cost and the second
a contribution towards an efficient waste management of this
undesirable material;
3. Except for stability at 30% volcanic ash content, the volcanic
ash percentages used did not move the volumetric properties
of the HMA outside Marshall mix design specification limits;
4. Obtained loss of indirect tensile strength results indicated
that using up to 10% granular volcanic ash will generate
mixes that have appropriate stripping resistance;
5. Mixes containing volcanic ash aggregate are expected to per-
form well in terms of creep resistance;
6. The use of up to 10% volcanic ash aggregate in asphalt con-
crete mixes will improve both the resilient modulus and fa-
tigue life; and
7. The asphalt concrete mix that has basalt aggregate, 10% vol-
canic ash aggregate, and basalt dust mineral filler was found
to be the optimal mix, i.e., it has the best mechanical prop-
erties among all the mixes included.
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