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Citation: Chowdhury, R.; Al Biruni,
M.T.; Afia, A.; Hasan, M.; Islam, M.R.;
Ahmed, T. Medical Waste
Incineration Fly Ash as a Mineral
Filler in Dense Bituminous Course in
Flexible Pavements. Materials 2023,
16, 5612. https://doi.org/10.3390/
ma16165612
Academic Editors: Rui Vasco Silva,
António P.C. Duarte and Miguel
Bravo
Received: 5 July 2023
Revised: 4 August 2023
Accepted: 7 August 2023
Published: 13 August 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
materials
Article
Medical Waste Incineration Fly Ash as a Mineral Filler in Dense
Bituminous Course in Flexible Pavements
Rumpa Chowdhury 1, Mir Tanvir Al Biruni 1, Antara Afia 1, Mehedi Hasan 1, Mohammed Russedul Islam 2
and Tanvir Ahmed 1,*
1Department of Civil Engineering, Bangladesh University of Engineering and Technology,
Dhaka 1000, Bangladesh; rumpa.ce.buet@gmail.com (R.C.); tanvirmir444@gmail.com (M.T.A.B.);
afia.tajalli@gmail.com (A.A.); mehedi@itn-buet.org (M.H.)
2Department of Civil Engineering, Military Institute of Science and Technology, Mirpur Cantonment,
Dhaka 1216, Bangladesh; russed@ce.mist.ac.bd
*Correspondence: tanvirahmed@ce.buet.ac.bd
Abstract:
Medical waste incineration fly ash (MWIFA) contains heavy metals that are toxic by nature
and pose numerous health risks. The paper deals with the suitability of MWIFA as a mineral filler
in the bituminous layer as an alternative to conventional stone dust (SD) through an appropriate
combination of engineering and environmental assessments. Engineering parameters, such as
Marshall stability, stability loss, flow, unit weight, air voids (V
a
), voids filled with asphalt (VFA),
and voids in the mineral aggregate (VMA) of the asphalt mixtures, were evaluated with varying
filler ratios, from 2% to 10%. All parameters for both fillers at optimum bitumen content satisfied
the Marshall Mix Design criteria. The optimum bitumen contents of all filler ratios were within the
standard limit recommended by the Bangladesh Roads and Highways Department. It was found that
mixes prepared with MWIFA can resist moisture effects, making them durable in the monsoon. The
mixes with 5.5% MWIFA as mineral filler performed the best, whereas 9% SD filler was required to
achieve similar performance. The environmental test results show no environmental restriction on
stabilizing the MWIFA into paving mixtures. The mobility of heavy metals (As, Pb, Cu, Cr, Ni, Cd,
Hg, and Zn) from the asphalt-MWIFA mix was insignificant. The cumulative concentrations of heavy
metals (Cd, Ni, Zn, Cu, and Pb) from long-term leaching tests were far below the Dutch regulatory
limit (U1). MWIFA can be considered an eco-friendly and sustainable mineral filler for the dense
bituminous pavement layer.
Keywords:
fly ash; mineral filler; sustainable pavement; Marshall properties; heavy metal leaching;
environmental impact
1. Introduction
Medical waste is a source of pollution and infection for humans and the natural
environment. With the rapid growth of healthcare facilities, enormous quantities of medical
waste are generated in Bangladesh, with an annual generation rate of 93,075 tons (average
rate of 0.8–1.67 kg/bed/day) [
1
,
2
]. The incineration of medical waste, followed by the
dumping of ash into landfills, is the most common practice for disposal [
3
]. The incineration
process can reduce waste by 70% but generates significant residual ashes [
4
]. The ashes
generated from medical waste incineration are enriched with heavy metals, and exposure to
these can cause damage to the environment and human health [
5
]. Fly ash can spread to a
greater distance by the wind, which helps them enter the food chain using the air, soil, and
surface water as exposure pathways and cause bioaccumulation in the food chain [
6
]. At
present, stabilization/solidification, one of the most renowned and appropriate pre-landfill
waste treatment techniques, has been adopted to alleviate the leaching toxicity of fly ash
and convert the heavy metals into a stabilized insoluble structure [
7
,
8
]. Medical Waste
Materials 2023,16, 5612. https://doi.org/10.3390/ma16165612 https://www.mdpi.com/journal/materials
Materials 2023,16, 5612 2 of 18
Incineration Fly Ash (MWIFA) can be successfully stabilized in construction materials using
cement, ceramic tiles, and synthetic geotextile [6,9,10].
Some recent research has focused on using waste materials in highway construction
and road layers from the top layer to the subgrade [
11
,
12
]. Studies on using waste material
in pavement construction are documented in the literature [
11
–
17
]. Using fly ash in asphalt
pavement is promising due to its positive impacts on the performances of asphalt concrete
mixtures and cost and eco-friendly characteristics [
18
]. Fly ash not only seals the voids in
the asphalt concrete mix but also provides contact points between larger aggregate particles
and thus can be an ideal filler material [
19
]. Fly ash has been found to provide good stability
in asphalt mixtures [
18
,
20
,
21
]. Mistry and Roy [
22
] found that fly ash in hot mix asphalt
(HMA) provides lesser deformation with good strength properties.
Filler is a crucial component of the asphalt paving mix, and it modulates the properties
of asphalt concrete mixtures [
23
]. Well-packed aggregates (coarse and fine aggregates)
combined with filler are the backbone of the asphalt mixture [
24
]. The mixture of asphalt
binder and mineral filler controls the complete performance of pavement mixtures [
25
].
Filler controls the mechanical properties of asphalt mixtures by providing additionalcontact
points between larger aggregates and increasing the viscosity of asphalt binders [
26
,
27
].
The Asphalt Institute recommends 4% to 8% filler usage in asphalt concrete [28].
Several researchers have investigated the suitability of using fly ash as mineral filler
in bituminous mixes in recent years. Fly ash from the combustion of pulverized coal [
29
],
thermal power plants [
30
,
31
], incinerated domestic and industrial products and wastewater
sludge [
32
], burning coal [
33
], municipal solid waste incineration [
34
], and burning crude
oil [
35
] have been used to evaluate and improve bituminous mixes performance in asphalt
pavement. Sobolev et al. [
36
] studied the viability of fillers, i.e., fly ash, lime, and cement
in asphalt concrete and demonstrated that adding these fillers improved the rheological
properties of the asphalt. Al-Hdabi [
37
] found that using rice husk ash as a mineral filler
improved the Marshall stability of hot asphalt mixtures more than conventional mineral
fillers. Radwan et al. [
38
] found higher stability values and lower flow values for the
coal fly ash mixes than conventional filler. The mixes showed strong moisture resistance
and durability, which validated the suitability of coal fly ash filler for HMA mixes. Zhao
et al. [
39
] showed that asphalt mixture with fly ash had more thermal susceptibility but
recommended a maximum 25% fly ash ratio considering moisture intrusion.
The physical, chemical, rheological, and mechanical properties of asphalt mixtures
containing fly ash from municipal solid waste used as a substitute for fine aggregate
or filler material have been explored [
32
,
39
–
43
]. Owing to the attractive outcomes of
these studies, the probability of using fly ash from medical waste incineration, which is
highly contaminated compared to municipal solid waste in nature, as a filler material
in similar applications appears to be highly promising. MWIFA as a filler material in
pavement construction is comparatively recent. Only a few studies have demonstrated its
feasibility as a paving material. Jaber et al. [
44
] studied the suitability of using residual
ashes from medical waste in the base layer of pavement, and a ratio of 25% of the ashes was
recommended based on Marshall properties only. According to prior experimental findings,
it might be feasible for toxic MWIFA to be used as a filler material. Most studies on fly ash
stabilization in asphalt pavements are confined to assessing engineering suitability without
considering the environmental effects after stabilization for long-term usage. MWIFA is
hazardous, and its leaching activity can cause several adverse impacts on human health and
the environment [
5
,
6
]. To our knowledge, no study assessed the environmental effects of
incorporating hazardous MWIFA in pavement construction. There are substantial research
deficiencies in computing the environmental impacts of MWIFA-incorporated pavements,
which require further investigation. Hence, a combination of appropriate environmental
tests is required to evaluate the suitability of using MWIFA as filler material in bituminous
mixes.
The materials used as common fillers, such as cement, limestone, and granite powder,
are not easily and economically available in countries such as Bangladesh [
15
]. Therefore,
Materials 2023,16, 5612 3 of 18
fly ash can be an economical alternative to more expensive filler materials. This study
investigates the environmental compatibility of stabilized MWIFA as a mineral filler in the
bituminous layer as an alternative to conventional fillers. The Marshall and leaching prop-
erties of asphalt paving mixes containing different proportions of MWIFA and stone dust
(SD) were determined and compared with available standards and guidelines. Marshall
mix designs using MWIFA and SD as fillers were performed to determine the optimum
bitumen and filler contents. The heavy metal leaching characteristics of the solidified
asphalt fly ash matrix were investigated to evaluate the environmental impacts. The results
of this study will contribute to the developing knowledge of the engineering feasibility
and environmental impacts of using fly ash from hazardous medical waste incineration in
pavement construction.
2. Methods and Materials
2.1. Test Scheme
Figure 1presents an outline of the tests required in this research. The details will be
described in the following sections.
Materials 2023, 16, x FOR PEER REVIEW 3 of 18
The materials used as common llers, such as cement, limestone, and granite pow-
der, are not easily and economically available in countries such as Bangladesh [15]. There-
fore, y ash can be an economical alternative to more expensive ller materials. This study
investigates the environmental compatibility of stabilized MWIFA as a mineral ller in
the bituminous layer as an alternative to conventional llers. The Marshall and leaching
properties of asphalt paving mixes containing dierent proportions of MWIFA and stone
dust (SD) were determined and compared with available standards and guidelines. Mar-
shall mix designs using MWIFA and SD as llers were performed to determine the opti-
mum bitumen and ller contents. The heavy metal leaching characteristics of the solidi-
ed asphalt y ash matrix were investigated to evaluate the environmental impacts. The
results of this study will contribute to the developing knowledge of the engineering feasi-
bility and environmental impacts of using y ash from hazardous medical waste incinera-
tion in pavement construction.
2. Methods and Materials
2.1. Test Scheme
Figure 1 presents an outline of the tests required in this research. The details will be
described in the following sections.
Figure 1. Flow chart showing the test outline.
2.2. Bitumen
Considering the weather paern and trac volume of Bangladesh, 60/70 grade bitu-
men was used in this study. The properties of bitumen used in the asphalt mix with
AASHTO standard designations are given in Table 1. All the properties except solubility
are within the standard ranges. The lower solubility value than the standard could be due
to mineral impurities in the bitumen.
Figure 1. Flow chart showing the test outline.
2.2. Bitumen
Considering the weather pattern and traffic volume of Bangladesh, 60/70 grade
bitumen was used in this study. The properties of bitumen used in the asphalt mix with
AASHTO standard designations are given in Table 1. All the properties except solubility
are within the standard ranges. The lower solubility value than the standard could be due
to mineral impurities in the bitumen.
Materials 2023,16, 5612 4 of 18
Table 1. Properties of bitumen and aggregate.
Properties Test Designation Sample Values Standard Specifications
Bitumen
Penetration at 25 ◦C (0.1 mm) AASHTO T49 61 60–70 a
Flash Point (◦C) AASHTO T48 295 min 232 a
Ductility at 25 ◦C (cm) AASHTO T51 100+ min 100 a
Solubility in Trichloroethylene (%) AASHTO T44 97.8 min 99.0 a
Loss on Heating (%) AASHTO T179 0.06 <0.8 a
Softening Point (◦C) AASHTO T53 49 48–56 a
Aggregate
Aggregate Impact Value (%) BS 812-3 28 <30 b
Aggregate Crushing Value (%) BS 812-3 17 <30 c
Ten Percent Fine Value (KN) BS 812-111 130 min 100 b
Flakiness Index (%) BS 812-105.1 26 <30 b
Elongation Index (%) BS 812-105.2 29 <30 b
Angularity Number BS 812-1 11 0–12 b
Los Angeles Abrasion (%) AASHTO T96 31 <35 c
Specific Gravity (CA) AASHTO T85 2.72 -
Specific Gravity (FA) AASHTO T84 2.6 -
a
AASHTO M 20-70 (2004). Standard Specification for Penetration Graded Asphalt Cement. American Association
of State and Highway Transportation Officials.
b
BS 882 (1992). Specification for aggregates from natural sources
for concrete.
c
RHD (2011). Standard specifications for pavement work, Ministry of Communications Roads and
Highways Department, Bangladesh.
2.3. Aggregates
The aggregate gradation used in this study is shown in Figure 2, which fulfills the
ASTM D3515-01 [
45
] hot mix paving mixtures standard specification criteria for the dense
mixture (mix designation D-4). An equal portion of fine aggregate was substituted by filler
material while increasing the filler ratios to keep the specified total aggregate quantity
constant. Table 1shows the aggregate properties, test specifications, and standard limits.
All aggregate properties were within standards set by RHD and BS. Stone chips were dried
to a constant temperature of from 105
◦
C to 110
◦
C (220
◦
F to 230
◦
F) and separated by
dry-sieving into the desired size fraction for the aggregate preparation.
Materials 2023, 16, x FOR PEER REVIEW 4 of 18
Table 1. Properties of bitumen and aggregate.
Properties
Test Designation
Sample Values
Standard Specifications
Bitumen
Penetration at 25 °C (0.1 mm)
AASHTO T49
61
60–70 a
Flash Point (°C)
AASHTO T48
295
min 232 a
Ductility at 25 °C (cm)
AASHTO T51
100+
min 100 a
Solubility in Trichloroethylene
(%)
AASHTO T44
97.8
min 99.0 a
Loss on Heating (%)
AASHTO T179
0.06
<0.8 a
Softening Point (°C)
AASHTO T53
49
48–56 a
Aggregate
Aggregate Impact Value (%)
BS 812-3
28
<30 b
Aggregate Crushing Value (%)
BS 812-3
17
<30 c
Ten Percent Fine Value (KN)
BS 812-111
130
min 100 b
Flakiness Index (%)
BS 812-105.1
26
<30 b
Elongation Index (%)
BS 812-105.2
29
<30 b
Angularity Number
BS 812-1
11
0–12 b
Los Angeles Abrasion (%)
AASHTO T96
31
<35 c
Specific Gravity (CA)
AASHTO T85
2.72
-
Specific Gravity (FA)
AASHTO T84
2.6
-
a AASHTO M 20-70 (2004). Standard Specication for Penetration Graded Asphalt Cement. Ameri-
can Association of State and Highway Transportation Ocials. b BS 882 (1992). Specication for ag-
gregates from natural sources for concrete. c RHD (2011). Standard specications for pavement
work, Ministry of Communications Roads and Highways Department, Bangladesh.
2.3. Aggregates
The aggregate gradation used in this study is shown in Figure 2, which fullls the
ASTM D3515-01 [45] hot mix paving mixtures standard specication criteria for the dense
mixture (mix designation D-4). An equal portion of ne aggregate was substituted by ller
material while increasing the ller ratios to keep the specied total aggregate quantity
constant. Table 1 shows the aggregate properties, test specications, and standard limits.
All aggregate properties were within standards set by RHD and BS. Stone chips were
dried to a constant temperature of from 105 °C to 110 °C (220 °F to 230 °F) and separated
by dry-sieving into the desired size fraction for the aggregate preparation.
Figure 2. Gradation of combined aggregate.
Figure 2. Gradation of combined aggregate.
Materials 2023,16, 5612 5 of 18
2.4. Preparation of MWIFA and SD Fillers
The methodology proposed by Tang et al. [
46
] was implemented to process the fly ash
sample into filler material. Fly ash samples were dried at 105
◦
C for 24 h, cooled at room
temperature, and passed through ASTM standard test sieves (#4, #8, #16, #30, #50, #100,
and #200) using a mechanical sieve shaker. As per ASTM D242 [
47
], finely separated fly ash
or stone dust with a mass ranging from 70% to 100% passing through a #200 (75
µ
m) sieve
can be used as mineral filler in asphalt mixes. This study used the sample portion passing
through the #200 sieve (75 microns) in asphalt mixtures as a mineral filler. The SD filler
was collected from the local market and similarly processed. Pictures of both fillers after
sieving are shown in Figure 3a,b. The filler samples were stored in an air-tight container to
keep them dry before experiments.
Materials 2023, 16, x FOR PEER REVIEW 5 of 18
2.4. Preparation of MWIFA and SD Fillers
The methodology proposed by Tang et al. [46] was implemented to process the y
ash sample into ller material. Fly ash samples were dried at 105 °C for 24 h, cooled at
room temperature, and passed through ASTM standard test sieves (#4, #8, #16, #30, #50,
#100, and #200) using a mechanical sieve shaker. As per ASTM D242 [47], nely separated
y ash or stone dust with a mass ranging from 70% to 100% passing through a #200 (75
μm) sieve can be used as mineral ller in asphalt mixes. This study used the sample por-
tion passing through the #200 sieve (75 microns) in asphalt mixtures as a mineral ller.
The SD ller was collected from the local market and similarly processed. Pictures of both
llers after sieving are shown in Figure 3a,b. The ller samples were stored in an air-tight
container to keep them dry before experiments.
Figure 3. Images of (a) MWIFA and (b) SD ller materials.
2.5. Properties of Mineral Fillers
Table 2 presents the chemical composition of MWIFA and SD obtained from XRF-
Spectrometer analysis. It can be seen that the signicant elements of MWIFA are CaO, SiO2
and SO3, while the signicant elements of SD are SiO2, CaO, Al2O3, Fe2O3 and MgO. In
MWIFA, the (SiO2 + Al2O3 + Fe2O3) content is 14.40%, less than 50%, and SiO3 exceeds 5%.
According to ASTM C618-19 [48] standard classication, MWIFA cannot be considered
class F or C y ash. The chemical composition of mineral ller controls the ller properties
and aects the adhesion properties of the asphalt mixtures [49]. As y ash comprises a
high content of CaO (62.39%), it can be used in asphalt mixtures with highly adhesive
aggregates and a bituminous binder, positively aecting mixture stability [31]. The spe-
cic gravity of SD ller is 2.79, which is slightly higher than that of MWIFA (sp. gravity =
2.57). ASTM C188-16 [50] and ASTM D854-02 [51] standard test procedures were followed
to determine the specic gravity of MWIFA and SD llers, respectively.
Table 2. Chemical composition (wt%) of MWIFA and SD.
Chemical Components
MWIFA
SD
CaO
62.39
25.53
SiO2
8.92
51.71
SO3
5.92
0.61
Na2O
5.35
0.10
TiO2
3.73
0.79
Al2O3
3.73
6.17
MgO
2.65
5.50
Figure 3. Images of (a) MWIFA and (b) SD filler materials.
2.5. Properties of Mineral Fillers
Table 2presents the chemical composition of MWIFA and SD obtained from XRF-
Spectrometer analysis. It can be seen that the significant elements of MWIFA are CaO, SiO
2
and SO
3
, while the significant elements of SD are SiO
2
, CaO, Al
2
O
3
, Fe
2
O
3
and MgO. In
MWIFA, the (SiO
2
+ Al
2
O
3
+ Fe
2
O
3
) content is 14.40%, less than 50%, and SiO
3
exceeds
5%. According to ASTM C618-19 [
48
] standard classification, MWIFA cannot be considered
class F or C fly ash. The chemical composition of mineral filler controls the filler properties
and affects the adhesion properties of the asphalt mixtures [
49
]. As fly ash comprises a high
content of CaO (62.39%), it can be used in asphalt mixtures with highly adhesive aggregates
and a bituminous binder, positively affecting mixture stability [
31
]. The specific gravity of
SD filler is 2.79, which is slightly higher than that of MWIFA (sp. gravity = 2.57). ASTM
C188-16 [
50
] and ASTM D854-02 [
51
] standard test procedures were followed to determine
the specific gravity of MWIFA and SD fillers, respectively.
The external morphology (texture) and particle shape analyzed using SEM are shown
in Figure 4a–d (Figure S1). The SEM images of MWIFA reveal that the particles have
irregular shapes and assorted sizes. The surface texture of MWIFA seems rough, and the
internal space between particles can be visibly detected. In contrast, the particles of SD
have angular and prismatic shapes with smooth surface textures.
Materials 2023,16, 5612 6 of 18
Table 2. Chemical composition (wt%) of MWIFA and SD.
Chemical Components MWIFA SD
CaO 62.39 25.53
SiO28.92 51.71
SO35.92 0.61
Na2O 5.35 0.10
TiO23.73 0.79
Al2O33.73 6.17
MgO 2.65 5.50
ZnO 2.13 -
Fe2O31.75 6.11
P2O51.38 0.19
K2O 1.19 2.16
NiO 0.50 -
Cr2O30.21 0.07
MnO 0.07 0.10
CuO 0.04 -
Br 0.03 -
ZrO2- 0.01
SrO - 0.05
Materials 2023, 16, x FOR PEER REVIEW 6 of 18
ZnO
2.13
-
Fe2O3
1.75
6.11
P2O5
1.38
0.19
K2O
1.19
2.16
NiO
0.50
-
Cr2O3
0.21
0.07
MnO
0.07
0.10
CuO
0.04
-
Br
0.03
-
ZrO2
-
0.01
SrO
-
0.05
The external morphology (texture) and particle shape analyzed using SEM are shown
in Figure 4a–d (Figure S1). The SEM images of MWIFA reveal that the particles have ir-
regular shapes and assorted sizes. The surface texture of MWIFA seems rough, and the
internal space between particles can be visibly detected. In contrast, the particles of SD
have angular and prismatic shapes with smooth surface textures.
Figure 4. SEM images of (a) MWIFA ller (10,000× magnication) (b) MWIFA ller (30,000× magni-
cation) (c) SD ller (10,000× magnication) (d) SD ller (25,000× magnication).
2.6. Marshall Mix Design
Three dierent types of specimens, namely (a) reference specimen using conven-
tional ller (stone abrasion dust), (b) modied specimen using varying proportions of
MWIFA as ller, and (c) control specimen without any ller, were prepared for testing as
per ASTM D6926-20 [52] to observe and compare the eect of using MWIFA instead of
conventional ller material. Filler contents were varied to determine the optimum ller
content as 0% (control), 2%, 4%, 6%, 8%, and 10%, slightly extending the recommended
ller range by Asphalt Institute. The specimens were prepared with 4.0%, 4.5%, 5.0%,
(a)
(b)
(c)
(d)
Figure 4.
SEM images of (
a
) MWIFA filler (10,000
×
magnification) (
b
) MWIFA filler (30,000
×
magnification) (c) SD filler (10,000×magnification) (d) SD filler (25,000×magnification).
2.6. Marshall Mix Design
Three different types of specimens, namely (a) reference specimen using conventional
filler (stone abrasion dust), (b) modified specimen using varying proportions of MWIFA as
filler, and (c) control specimen without any filler, were prepared for testing as per ASTM
D6926-20 [
52
] to observe and compare the effect of using MWIFA instead of conventional
filler material. Filler contents were varied to determine the optimum filler content as 0%
(control), 2%, 4%, 6%, 8%, and 10%, slightly extending the recommended filler range by
Asphalt Institute. The specimens were prepared with 4.0%, 4.5%, 5.0%, 5.5%, and 6.0%
Materials 2023,16, 5612 7 of 18
of the binder for each proportion of filler. All specimens were tested according to ASTM
D1559 [
53
] (Marshall Mix Design Method). The Marshall stability and flow tests were
performed to determine the mechanical properties of the samples according to ASTM
D6927-15 [
54
], and their corresponding maximum load resistance and flow values were
recorded. The bulk specific gravity and density, percent air voids, and theoretical maximum
specific gravity were determined for the volumetric analysis of each specimen.
2.7. Immersion Test
Following the methodology proposed by Akbulut et al. [
55
], Marshall immersion tests
were performed to inspect the deviations in the properties of hot bituminous mixtures
under the effect of moisture. Specimens with varying filler ratios were produced using their
optimum bitumen contents and cured for 48 h in a water bath at 60
◦
C. After the curing,
the Marshall stability test was performed. The stability loss is defined as the reduction in
stability after immersion in hot water for 48 h.
2.8. Determination of Optimum Filler Percentage
If the filler ratio is not optimized in hot bituminous mixtures, it can adversely af-
fect the performance of the mix [
56
]. The optimum filler content is determined using
Equation (1) [55] as follows:
Optimum Filler Content (%) = (Fs+Fmi +Fd+Fv)
4(1)
Here, F
s
is the filler content corresponding to maximum stability; F
mi
is the filler
content corresponding to minimum stability loss (determined from the Marshall mechan-
ical immersion test); F
d
is the filler content corresponding to maximum unit weight; F
v
is the filler content corresponding to the minimum percentage of voids in mineral aggre-
gate. F
s
is selected to obtain the maximum stability, F
mi
is selected to ensure minimum
water susceptibility, and the other two parameters are selected to obtain the most tightly
packed mix.
2.9. Leaching Test
USEPA 1311 [
57
] protocol (Toxicity Characteristics Leaching Procedure (TCLP)) was
used to determine the leaching potential. Samples were dried in an oven at 105
◦
C until
constant weight, lightly ground for homogenization and crushed to a particle size smaller
than 9.5 mm. The extraction fluid (pH of 2.88
±
0.05) was added to a zero-headspace
extractor (ZHE) at a liquid–solid ratio of 20:1, and the samples were agitated with a National
Bureau of Standards (NBS) rotary tumbler for 18 h at 30
±
2 rpm. The leachate was filtered
with 0.45
µ
m pore size filter paper and analyzed for selected heavy metals (As, Cr, Cd, Cu,
Hg, Ni, Pb and Zn) using Atomic Absorption Spectroscopy (AAS) (Shimadzu AA 6800).
The Dutch tank test (NEN 7345 [
58
]) was used to evaluate the leaching performance of
stabilized samples over a large period (64 days). Two leaching limits (U1 and U2) were
used to categorize the environmental impact of the materials [
59
]. The sample was put in
a polyethylene container and filled with acidified water (HNO
3
at pH = 4). The leachate
was removed and replaced with fresh extractant fluid eight times after 0.25, 1, 2.25, 4, 9, 16,
36, and 64 days. Leachate obtained from each extraction was analyzed for heavy metals.
Equation (2) was used to compute the leachability of each pollutant (heavy metals) at the
ith extraction [60].
Ei=(Ci−Co)V
1000A(2)
Here, E
i
= leachability of a pollutant at the i-th extraction (mg/m
2
), C
i
= pollutant
concentration at the i-th extraction (mg/L), C
o
= pollutant concentration in the blank
(mg/L), V= volume of extractant agent (L), A= surface area of the sample (m2).
Materials 2023,16, 5612 8 of 18
After eight extractions, Equation (3) was used to compute the leachability (E) for the
heavy metals [60].
E=
8
∑
i=1
Ei(3)
3. Results and Discussion
3.1. Unit Weight
The relationship between unit weight and the bitumen content in the bituminous
mixes for MWIFA and SD filler is shown in Figure 5a,b. The unit weight increased with the
increase in asphalt content for both fillers. The increasing bitumen content fills the voids,
increasing the unit weight in the mix [
15
]. Similar results were observed in the studies
using fly ash, SD, brick dust and cement as fillers in the hot bituminous mixes [
15
,
61
,
62
].
In the case of MWIFA, the maximum unit weight was found in 4% filler (8% for SD filler),
indicating that the most compact mix is obtained in this filler ratio. MWIFA enters the
voids between sand particles, thus raising the density and unit weight. However, MWIFA,
being more irregularly shaped than SD, thrusts out the sand particles while forming more
voids, consequently decreasing the unit weight. Mazumdar and Rao [
63
] observed similar
behavior with other fly ash forms.
Materials 2023, 16, x FOR PEER REVIEW 8 of 18
E=
∑
𝐸𝑖
8
𝑖=1
(3)
3. Results and Discussion
3.1. Unit Weight
The relationship between unit weight and the bitumen content in the bituminous
mixes for MWIFA and SD ller is shown in Figure 5 a,b. The unit weight increased with
the increase in asphalt content for both llers. The increasing bitumen content lls the
voids, increasing the unit weight in the mix [15]. Similar results were observed in the stud-
ies using y ash, SD, brick dust and cement as llers in the hot bituminous mixes
[15,61,62]. In the case of MWIFA, the maximum unit weight was found in 4% ller (8% for
SD ller), indicating that the most compact mix is obtained in this ller ratio. MWIFA
enters the voids between sand particles, thus raising the density and unit weight. How-
ever, MWIFA, being more irregularly shaped than SD, thrusts out the sand particles while
forming more voids, consequently decreasing the unit weight. Mazumdar and Rao [63]
observed similar behavior with other y ash forms.
Figure 5. Relationships between unit weight and bitumen content for (a) MWIFA ller and (b) SD
ller, and between Marshall stability and bitumen content for (c) MWIFA ller and (d) SD ller.
(a)
(b)
(c)
(d)
Figure 5.
Relationships between unit weight and bitumen content for (
a
) MWIFA filler and (
b
) SD
filler, and between Marshall stability and bitumen content for (c) MWIFA filler and (d) SD filler.
Materials 2023,16, 5612 9 of 18
3.2. Stability
The stability property of the bituminous mix indicates the pavements’ resistance to
traffic-induced stresses [
55
]. The relationships between the stability values and bitumen
contents for MWIFA and SD fillers are depicted in Figure 5c,d. The stability values of all
hot mix samples, except the one with 10% MWIFA, initially increase with bitumen content
and decrease after reaching a peak. The 2% and 8% SD samples follow the same pattern.
Sutradhar et al. [
14
], Kar et al. [
61
], Saltan et al. [
11
], Jony et al. [
64
], Rahman et al. [
62
], and
Mistry and Roy [
22
] found similar stability results for their respective experiments with
asphalt mixes. On the other hand, the stability values decrease with increasing asphalt
binder content for 4%, 6%, and 10% SD filler ratios. Although the stability graphs of MWIFA
and SD fillers follow different trends, all the Marshall stability values meet the minimum
Marshall mix design criteria (5.34 kN) recommended by the Asphalt Institute.
The maximum stability values of mixes with 0%, 2%, 4%, 6%, 8%, and 10% MWIFA
filler are found to be 22.37 kN, 21.47 kN, 23.82 kN, 20.11 kN, 19.70 kN, and 25.80 kN,
respectively. Fly ash filler goes into the voids of FA and interlocks the particles, which may
cause an initial increase in stability values [
63
]. The maximum stability values of mixes with
2%, 4%, 6%, 8%, and 10% SD filler are 25.15 kN, 22.68 kN, 20.75 kN, 23.78 kN, and 27.82 kN,
respectively. The bitumen content corresponding to the maximum stability is higher for
the mixes containing MWIFA filler than those with SD filler, and the maximum stability
values of SD filler mixes are comparatively higher, as seen in Figure 5c,d. For example, if
we choose a 2% filler content, the corresponding bitumen content for maximum stability of
the MWIFA mix (21.47 kN) is 5%, while for maximum stability of the SD mix (25.15 kN), it
is 4.5%. This phenomenon is the same for other filler contents. This may be because SD
filler produces a viscous asphalt cement mixture with lower bitumen content [
15
]. It is
possible that the greater dispersion of binders in asphalt mixes having SD as a filler confers
more stiffness and, consequently, more stability [65].
3.3. Flow
The flow value denotes the vertical deformation under maximum load. It signifies
that bituminous mixtures’ plasticity and flexibility properties are inversely related to
internal friction [
11
]. Figure 6a,b illustrates the relationship between the Marshall flow
value and bitumen content with varying MWIFA and SD fillers. The flow values for both
filler materials, except the 8% MWIFA filler ratio, follow the general trend of a consistent
rise with the increasing bitumen contents. Uzun and Terzi [
66
], Sutradhar et al. [
15
] and
Kar et al. [
61
] found that the flow values increased with the increase in bitumen contents in
their studies. For the case of 8% MWIFA, the decrease in flow values may be ascribed to
the increased interlocking offered by fly ash particles, and the successive rise in the flow
values may be because of the large surface area, resulting in insufficient coating [
63
]. All
the flow values for all filler percentages closely comply with the Marshall mix design limit
(from 2 mm to 4 mm) of the Asphalt Institute [67].
3.4. Air Voids
The presence of air voids in a dense-graded mix prevents the pavement from flushing,
shoving, and rutting. Figure 6c,d shows the relationship between the percentage of air void
and bitumen content with MWIFA and SD fillers. The percentage of air voids decreases
with the increase in bitumen contents for both fillers. An increased bitumen content reduces
air voids by filling more voids in the paving mixture. Nayak and Mohanty [
68
], Uzun and
Terzi [
66
], Kar et al. [
61
], and Mazumdar and Rao [
63
] found a similar decreasing trend of
air voids with increased bitumen content, with fly ash and SD as mineral fillers. Adding
filler to hot bituminous mixtures eases the compensation of fine aggregates in the mix, and
thus voids in the mixtures reduce with the increase in filler proportions [
15
]. Except for
a few ratios, mixes with MWIFA filler ratios have comparatively higher air voids values
than those with the same SD filler ratios. The differences in size, shape, surface structure
and physio-chemical properties between the MWIFA and SD fillers could be responsible
Materials 2023,16, 5612 10 of 18
for this Marshall property variation [
62
,
69
]. Zulkati et al. [
24
] mentioned that some fillers
create stiff asphalt mastic and require greater compaction effort. It is possible that SD, being
less fine than MWIFA, has lower air void values in Marshall samples despite having the
same mix proportions and compaction energies. All the air voids values except for a few
percentages for both fillers are within the standard Marshall mix design limit (3 to 5), and
an OBC value was calculated from the test results for each filler type and ratio according to
the Marshall mix design method.
Materials 2023, 16, x FOR PEER REVIEW 10 of 18
Figure 6. Relationships between Marshall ow value and bitumen content for (a) MWIFA ller and
(b) SD ller, and between air voids and bitumen content for (c) MWIFA ller and (d) SD ller.
3.4. Air Voids
The presence of air voids in a dense-graded mix prevents the pavement from ush-
ing, shoving, and ruing. Figure 6c,d shows the relationship between the percentage of
air void and bitumen content with MWIFA and SD llers. The percentage of air voids
decreases with the increase in bitumen contents for both llers. An increased bitumen
content reduces air voids by lling more voids in the paving mixture. Nayak and Mohanty
[68], Uzun and Terzi [66], Kar et al. [61], and Mazumdar and Rao [63] found a similar
decreasing trend of air voids with increased bitumen content, with y ash and SD as min-
eral llers. Adding ller to hot bituminous mixtures eases the compensation of ne aggre-
gates in the mix, and thus voids in the mixtures reduce with the increase in ller propor-
tions [15]. Except for a few ratios, mixes with MWIFA ller ratios have comparatively
higher air voids values than those with the same SD ller ratios. The dierences in size,
shape, surface structure and physio-chemical properties between the MWIFA and SD ll-
ers could be responsible for this Marshall property variation [62,69]. Zulkati et al. [24]
mentioned that some llers create sti asphalt mastic and require greater compaction ef-
fort. It is possible that SD, being less ne than MWIFA, has lower air void values in Mar-
shall samples despite having the same mix proportions and compaction energies. All the
air voids values except for a few percentages for both llers are within the standard Mar-
shall mix design limit (3 to 5), and an OBC value was calculated from the test results for
each ller type and ratio according to the Marshall mix design method.
(a)
(b)
(c)
(d)
Figure 6.
Relationships between Marshall flow value and bitumen content for (
a
) MWIFA filler and
(b) SD filler, and between air voids and bitumen content for (c) MWIFA filler and (d) SD filler.
3.5. Voids in Mineral Aggregate (VMA)
An adequate VMA is necessary to ensure the film thickness within the mix without
too much asphalt bleeding or flushing, ensuring durability in the mix [
66
,
70
]. Figure 7a,b
depicts the relationship between VMA (%) and bitumen content with varying MWIFA and
SD fillers. All the VMA (%) values for both fillers, except a few values for SD filler, satisfy
the Marshall minimum design requirement of 13% (the horizontal line in Figure 7a,b) for
VMA recommended by the Asphalt Institute. The VMA has been found to decrease with
increasing asphalt content, reach a minimum, and subsequently increase for both fillers
except for the 6% and 8% of MWIFA filler ratios. VMA initially decreases due to better
compaction and rises again as the extra bitumen in the mix pushes apart the aggregates [
67
].
Previous studies found a decreasing trend of %VMA values to the increasing bitumen
contents in paving mixtures with various fly ashes and SD as mineral fillers [15,61,62,64].
Materials 2023,16, 5612 11 of 18
Materials 2023, 16, x FOR PEER REVIEW 11 of 18
3.5. Voids in Mineral Aggregate (VMA)
An adequate VMA is necessary to ensure the lm thickness within the mix without
too much asphalt bleeding or ushing, ensuring durability in the mix [66,70]. Figure 7a,b
depicts the relationship between VMA (%) and bitumen content with varying MWIFA and
SD llers. All the VMA (%) values for both llers, except a few values for SD ller, satisfy
the Marshall minimum design requirement of 13% (the horizontal line in Figure 7a,b) for
VMA recommended by the Asphalt Institute. The VMA has been found to decrease with
increasing asphalt content, reach a minimum, and subsequently increase for both llers
except for the 6% and 8% of MWIFA ller ratios. VMA initially decreases due to beer
compaction and rises again as the extra bitumen in the mix pushes apart the aggregates
[67]. Previous studies found a decreasing trend of %VMA values to the increasing bitumen
contents in paving mixtures with various y ashes and SD as mineral llers [15,61,62,64].
Figure 7. Relationships between voids in mineral aggregate and bitumen content for (a) MWIFA
ller and (b) SD ller, and between voids lled with asphalt and asphalt content for (c) MWIFA
ller and (d) SD ller. The horizontal line in (a,b) represents the minimum Marshall mix design
requirement for VMA. The horizontal lines in (c,d) represent the upper and lower limits of VFA for
the Marshall mix design.
3.6. Voids Filled with Asphalt (VFA)
The VFA property regulates the plasticity, durability, and friction coecient of the
bituminous mixtures. The relationships between VFA and bitumen contents for MWIFA
(a)
(b)
(c)
(d)
Figure 7.
Relationships between voids in mineral aggregate and bitumen content for (
a
) MWIFA filler
and (
b
) SD filler, and between voids filled with asphalt and asphalt content for (
c
) MWIFA filler and
(
d
) SD filler. The horizontal line in (
a
,
b
) represents the minimum Marshall mix design requirement
for VMA. The horizontal lines in (
c
,
d
) represent the upper and lower limits of VFA for the Marshall
mix design.
3.6. Voids Filled with Asphalt (VFA)
The VFA property regulates the plasticity, durability, and friction coefficient of the
bituminous mixtures. The relationships between VFA and bitumen contents for MWIFA and
SD fillers percentages are shown in Figure 7c,d. The %VFA values of compacted mixtures
increase with bitumen contents for both fillers. This trend is consistent with previous
studies of paving mixtures with various fly ashes and SD as mineral fillers [
12
,
15
,
61
,
64
,
66
].
The VFA values for all samples are not within the Marshall mix design criteria of 65–78%
(horizontal lines in Figure 7c,d), specified by the Asphalt Institute. However, the VFA
design value obtained for the corresponding filler ratio is within the standard limit.
3.7. Marshall Properties at Optimum Bitumen Content (OBC)
The OBC for each filler percentage is defined as the respective bitumen content at
4% air voids. The properties of the mixes at their OBC with each filler type and contents
are shown in Table 3. All the OBC levels satisfy the Roads and Highway Department,
Bangladesh standard limit. No particular trend was observed in OBC values with the
increase in MWIFA or SD fillers (Table 3). It appears that, apart from 2% and 4% MWIFA
fillers, there is an increasing trend for OBC, but no such trend was observed for SD fillers.
The determination of OBC employs a graphical method (corresponds to 4% air voids in
the graph). If there are limited data, the determination could have some anomalies. It
Materials 2023,16, 5612 12 of 18
is possible that such anomalies masked the effect of the varying filler ratios. However,
the OBC requirement of MWIFA filler mixes was consistently higher than that of SD
filler. Joumblat et al. [
34
] also found a slight increase in the OBC values for the samples
modified with municipal solid waste incineration fly ash. Fly ash absorbs slightly more
bitumen than SD; therefore, it needs more asphalt to bind [
61
]. The high porosity, specific
surface area, surface roughness, and particle shape of the incineration fly ash can cause this
phenomenon [34].
Table 3. Volumetric and Marshall properties of bituminous mixes at OBC content.
Design Criteria OBC (%) %Va%VMA %VFA Stability (kN) Flow (mm) Stability Loss (%)
0% Filler 5.22 4 14.55 72.66 21.16 3.22 32.91%
2% MWIFA Filler 4.85 4 13.86 71.49 21.06 4.00 7.59%
4% MWIFA Filler 4.84 4 13.54 70.45 22.99 3.92 35.12%
6% MWIFA Filler 5.3 4 14.53 72.52 17.98 3.96 24.9%
8% MWIFA Filler 5.99 4 16.55 75.83 15.88 3.98 0.70%
10% MWIFA Filler 6.25 4 16.70 75.48 22.69 3.69 23.56%
2% SD Filler 4.51 4 13.24 69.80 25.06 4.24 31.35%
4% SD Filler 4.3 4 13.10 69.55 21.18 3.51 30.86%
6% SD Filler 4.7 4 13.77 71.95 18.37 4.00 21.86%
8% SD Filler 4.12 4 13.02 69.37 17.79 3.83 29.18%
10% SD Filler 4.37 4 13.42 70.47 25.27 3.53 12.52%
Standard limit a b 4.90–6.5 a3–5 bmin 13 b65–78 bmin 5.338 b2–4 b-
a
RHD (2011). Standard specifications for pavement work, Government of the People’s Republic of Bangladesh
Ministry of Communications Roads and Highways Department, Bangladesh.
b
Asphalt Institute (2014). MS-2
asphalt mix design methods (7th Edition). Asphalt Institute.
The Marshall Stability values of the mixes with MWIFA filler at the optimum bitumen
content are 15 kN to 23 kN (Table 3). On the other hand, the stability values vary from
17 kN to 25.5 kN for SD filler. Therefore, the SD filler exhibits slightly higher stability than
the MWIFA filler at OBC for most filler contents. However, the stability values of both
fillers at OBC meet the minimum Marshall mix design requirement of 5.34 kN.
In mixes including MWIFA filler, Marshall flow values at their respective OBC are
from 3.22 mm to 4.00 mm, whereas, for SD filler, this range is within 3.51–4.24 mm (Table 3).
The flow values of hot bituminous mixtures used in medium traffic surface and base must
be between 2 mm and 4 mm according to the Marshall mix design criteria of the Asphalt
Institute. The flow values of the two fillers at OBC generally conform to the Marshall mix
design limit. VFA for the OBC with 0%, 2%, 4%, 6%, 8% and 10% MWIFA filler is within
70.45–75.83%. For SD filler samples, this range is from 69.37% to 71.95% (Table 3). The
VFA values for both fillers at OBC have satisfied the Marshall mix design maximum and
minimum VFA requirements. In mixes including 0%, 2%, 4%, 6%, 8% and 10% MWIFA filler,
the VMA corresponding to the optimum level of bitumen is found within 13.54–16.70%
(Table 3). Design %VMA increases with an increase in MWIFA filler content. A similar
trend in VMA at OBC is also observed by Jony et al. [
64
] and Sargın et al. [
71
] in their
respective studies. For SD filler samples, this range is from 13.02% to 13.77% (Table 3).
The VMA values for samples with MWIFA are slightly higher than those with SD as filler.
Joumblat et al. [
34
] observed a similar result, where all samples modified with municipal
waste incineration fly ash showed higher VMA values. The VMA values for both fillers at
OBCs complied with the Marshall mix design minimum requirement of 13%.
3.8. Marshall Immersion
Mechanical immersion tests determine the loss of stability in hot bituminous mixtures
under moisture action. At OBC, there is no definite trend with stability loss in immersion
with the increase in filler content. However, mixes with MWIFA showed less immersion
loss than SD (Table 3). The Marshall stability loss is the lowest for the mix containing 8%
MWIFA among all mixtures prepared with both fillers (Table 3). Carpenter [
72
] found that
Materials 2023,16, 5612 13 of 18
fly ash favored retaining the compressive strength of asphalt concrete immersed in water.
The likely reason for this is that the predominant constituent in MWIFA is CaO, which ex-
hibits water-resistive properties regarding moisture stability in bituminous mixes [
73
]. On
the other hand, the asphalt mixture prepared with SD had comparatively low moisture re-
sistance and poor adherence with asphalt binder because of its high presence of SiO
2[49,74]
.
Akbulut et al. [
55
] found a similar trend of stability losses with the increasing granite sludge
filler ratios and obtained the minimum stability loss in the 8% filler-containing specimens.
3.9. Optimum Filler Content
The Optimum filler content (OFC), calculated using Equation (1), which corresponds
to maximum stability, lowest Marshall stability loss, maximum density and the lowest
percentage of voids in the hot bituminous mixtures, is 5.5% and 9%, respectively, for
MWIFA and SD fillers. The required optimum filler amount is lower in the asphalt mixes
with MWIFA filler than those containing SD filler. Several studies using fly ash as a mineral
filler obtained OFC values between 4% and 7% and exhibited better performance than
conventional fillers [67,75,76].
3.10. Heavy Metal Leaching
The concentration of leachates from raw fly ash and Marshall samples in standard
TCLP leaching test and a comparison with Land Disposal Restrictions Limits (LDR) for
hazardous wastes are given in Table 4. The concentrations of the heavy metals found in
raw fly ash and asphalt samples with MWIFA filler are far below the USEPA regulatory
limits. The maximum amount of As, Cr and Zn metals in MWIFA that could be reduced
was 37.3%, 94.4%, and 100%, respectively, when using a 2% filler in a bituminous mix. The
highest reduction for Pb (57.7%) was found in the mix containing 4% MWIFA filler, while
the maximum reduction in Cd (69.8%) was observed in the 6% MWIFA filler sample. There
was an increase in copper and nickel metals, probably from other constituents, but it did not
exceed the EPA Land Disposal limit. These results ensure that the leaching tendency of the
heavy metals from the asphalt paving mixture incorporating MWIFA is significantly lower
than in raw MWIFA. This suggests that MWIFA can be reliably used in paving mixtures
without any concerns for environmental hazards.
Table 4.
TCLP test results of raw MWIFA and MWIFA filler (units are in ppm, except heavy metals
reduction (%)).
Heavy Metals As Pb Cu Cr Cd Zn Ni Hg
Raw MWIFA 0.0298 0.169 0.003 0.054 0.106 0.011 0.003 ND a
MWIFA as filler in
Marshall Samples
2% filler 0.0187 0.16 0.059 0.003 0.089 0 0.377 ND
Heavy Metal Reduction (%) 37.3 5.3 - 94.4 16.0 100 - -
4% filler 0.0254 0.072 0.025 0.067 0.042 0.001 0.087 ND
Heavy Metal Reduction (%) 14.8 57.4 - - 60.4 90.9 - -
6% filler 0.0256 0.08 0.019 0.027 0.032 0.002 0.076 ND
Heavy Metal Reduction (%) 14.1 52.7 - 50 69.8 81.8 - -
8% filler 0.0688 0 0.01 0.009 0.085 0 0.045 ND
Heavy Metal Reduction (%) - 100 - 83.3 19.8 100 - -
10% filler 0.0251 0.125 0.012 0.07 0.048 0.002 0.15 ND
Heavy Metal Reduction (%) 15.8 26.0 - - 54.7 81.8 - -
EPA Land Disposal
Restriction for
Hazardous Waste b
Universal Treatment Standards
limit 5 0.75 - 0.6 0.11 4.3 11 0.2
Toxicity Characteristic Regulatory
Limit 5 5 - 5 1 - - 0.2
a
ND: Not Detected.
b
USEPA (1996). Land Disposal Restrictions for Hazardous Waste, United States Environmen-
tal Protection Agency.
Materials 2023,16, 5612 14 of 18
The cumulative leached concentrations of all the heavy metals were determined
using the Dutch tank test and summarized in Table 5. According to NEN 7345, if the
cumulative heavy metal concentrations of stabilized samples are below U1, the stabilized
waste can be used on land and construction material without restriction [
59
,
77
]. All the
cumulative concentrations are found far below the regulatory limit U1. Heavy metals
(Cd, Ni, Zn, Cu and Pb) leached insignificantly from monolithic asphalt specimens in
acidic water. Therefore, the inclusion of MWIFA in asphalt pavement can be considered
environmentally friendly.
Table 5. Results of the tank leaching tests in Marshall samples after eight extractions.
Heavy Metals Cd Ni Zn Cu Pb
Unit mg/m2mg/m2mg/m2mg/m2mg/m2
2% MWIFA 0.00018 0.00028 0.00002 0.00005 0.00034
4% MWIFA 0.00034 0.00022 0.00002 0.00005 0.00018
6% MWIFA 0.00022 0.00028 0.00001 0.00008 0.00040
8% MWIFA 0.00035 0.00027 0.00003 0.00015 0.00022
10% MWIFA 0.00022 0.00033 0.00002 0.00006 0.00041
Leaching limits as per NEN 7345 [58]
U1 1 50 200 50 100
U2 7 350 1500 350 800
4. Conclusions
4.1. Mechanical and Sustainable Performance
The study evaluates the environmental and physical performances of the bituminous
mixes prepared with MWIFA as mineral filler. The study concludes with the following
findings:
(1) All OBC values for mixes with MWIFA fall within the specified limits of the
Roads and Highways Department, Bangladesh, depicting compliance with the existing
practices. The Marshall properties, such as stability, flow, air voids, VMA and VFA at
respective OBCs, satisfy the criteria recommended by the Asphalt Institute for each of
the varying MWIFA filler ratios. MWIFA performs similarly to SD, verifying its potential
as an alternative filler in bituminous courses, especially in a country where the source of
traditional filler is limited.
(2) The OFC values for MWIFA and SD fillers are 5.5% and 9%, respectively. The
bituminous mixes with a 5.5% MWIFA filler would perform better in pavements, whereas
those with a 9% SD filler will exhibit the same performance. The optimum filler required in
asphalt concrete mixes for MWIFA is less than that of SD filler. So, the MWIFA filler could
be a promising substitute for SD, especially where SD is imported with foreign currency.
(3) The Marshall stability loss of mixes with MWIFA is less than that of SD, showing
its ability to protect against the moisture effect. So, using MWIFA as a mineral filler in the
pavement can be more suitable than conventional SD filler, especially in tropical areas.
(4) Leaching test results depict no environmental restrictions on using MWIFA in
asphalt pavement as filler. Long-term heavy metal leaching is negligible. The incorporated
MWIFA–asphalt matrix reduces the leachability of the toxic heavy metals contained in the
MWIFA. MWIFA will have no adverse impact on the environment after stabilization.
4.2. Practical Implications on the Utilization of MWIFA
From the evaluation of the test results, MWIFA can be used efficiently as a mineral
filler in the asphalt paving mix as a replacement for conventional SD filler, especially in
areas where MWIFA is abundantly available with affordable transportation costs. This can
also be an eco-friendly solution to medical waste disposal problems, especially for a country
with a scarcity of land to provide a landfill area. However, effective guidelines and policies
from the local government are needed to avoid potential confusion regarding its use. Such
Materials 2023,16, 5612 15 of 18
measures would lead to the greater consumption of MWIFA in the pavement industry and
reduce the demand for virgin materials, resulting in sustainable waste management.
4.3. Limitations and the Scope for the Future Studies
The conclusion of the paper is based on findings from environmental tests as well as the
observation of Marshall properties. Future works should consider some of the mechanical
properties obtained from Indirect Tensile Strength (ITS), Indirect Tensile Stiffness Modulus
(ITSM), Retained Marshall Stability (RMS), and Dynamic Modulus tests to assess the
long-term impact of MWIFA’s incorporation in asphalt mixes.
Supplementary Materials:
The following supporting information can be downloaded at: https://
www.mdpi.com/article/10.3390/ma16165612/s1, Figure S1: SEM image of MWIFA with 500
×
zoom; Figure S2: Prepared samples: (a) after demolding and (b) during submerged for SSD weight
calculation. Table S1: Mix proportions of the asphalt mixes for both fillers.
Author Contributions:
R.C.: Conceptualization, methodology, formal analysis, investigation, original
draft preparation; M.T.A.B.: investigation, data curation; A.A.: investigation, data curation; M.H.:
methodology, validation, supervision; M.R.I.: data curation, supervision, writing—reviewing and
editing; T.A.: conceptualization, supervision, writing—reviewing and editing, project administration.
All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement:
All data generated or analyzed during the study are included in this
manuscript.
Acknowledgments:
The authors acknowledge the assistance of the Transportation and Environmen-
tal Engineering Laboratories staff of BUET in carrying out this research. Graduate student funding
from CASR BUET is also acknowledged.
Conflicts of Interest: The authors declare they have no known competing financial interests.
References
1.
Syed, E.H.; Mutahara, M.; Rahman, M. Medical Waste Management (MWM) in Dhaka, Bangladesh. Home Health Care Manag.
Pract. 2012,24, 140–145. [CrossRef]
2.
Ministry of Health and Family Welfare, Environmental Assessment and Action Plan for the Health, Population and Nutrition Sector
Development Program (HPNSDP), 2011–2016; Environment Management Plan; Government of the People’s Republic of Bangladesh:
Dhaka, Bangladesh, 2011.
3.
Azni, I.; Katayon, S.; Ratnasamy, M.; Johari, M.M.N.M. Stabilization and utilization of hospital waste as road and asphalt
aggregate. J. Mater. Cycles Waste Manag. 2005,7, 33–37. [CrossRef]
4.
Zhao, L.; Zhang, F.-S.; Chen, M.; Liu, Z.; Wu, D.B.J. Typical pollutants in bottom ashes from a typical medical waste incinerator.
J. Hazard. Mater. 2010,173, 181–185. [CrossRef] [PubMed]
5.
Kimani, N.G. Environmental Pollution and Impacts on Public Health: Implications of the Dandora Municipal Dumping Site in Nairobi,
Kenya; Nairobi United Nations Environment Program: Nairobi, Kenya, 2007.
6.
Agamuthu, P.; Chitra, S. Solidification/stabilization disposal of medical waste incinerator fly ash using cement. Malays. J. Sci.
2009,28, 241–255. [CrossRef]
7.
Tzanakos, K.; Mimilidou, A.; Anastasiadou, K.; Stratakis, A.; Gidarakos, E. Solidification/stabilization of ash from medical waste
incineration into geopolymers. Waste Manag. 2014,34, 1823–1828. [CrossRef]
8.
Liu, F.; Liu, H.-Q.; Wei, G.-X.; Zhang, R.; Zeng, T.-T.; Liu, G.-S.; Zhou, J.-H. Characteristics and Treatment Methods of Medical
Waste Incinerator Fly Ash: A Review. Processes 2018,6, 173. [CrossRef]
9. Kumar, U.; Srivastava, V.; Singh, A.K. Suitability of biomedical waste ash in concrete. Int. J. Eng. Tech. Res. 2016,5, 2454–4698.
10.
Al-Mutairi, N.; Terro, M.; Al-Khaleefi, A.-L. Effect of recycling hospital ash on the compressive properties of concrete: Statistical
assessment and predicting model. Build. Environ. 2004,39, 557–566. [CrossRef]
11.
Huang, Y.; Bird, R.N.; Heidrich, O. A review of the use of recycled solid waste materials in asphalt pavements. Resour. Conserv.
Recycl. 2007,52, 58–73. [CrossRef]
12.
Saltan, M.; Öksüz, B.; Uz, V.E. Use of glass waste as mineral filler in hot mix asphalt. Sci. Eng. Compos. Mater.
2015
,22, 271–277.
[CrossRef]
Materials 2023,16, 5612 16 of 18
13.
Kandhal, P.S. Waste Materials in Hot Mix Asphalt—An Overview; National Center for Asphalt Technology: Auburn, AL, USA, 1992.
14.
Amir, M.; Morteza, R. Application of coal waste powder as filler in hot mix asphalt. Constr. Build. Mater.
2014
,66, 476–483.
[CrossRef]
15.
Alnealy, D.S.K.T.; Sutradhar, D.; Miah, M.; Chowdhury, G.J.; Sobhan, M.A. Effect of Using Waste Material as Filler in Bituminous
Mix Design. Am. J. Civ. Eng. 2015,3, 88–94. [CrossRef]
16.
Bhageerathy, K.P.; Alex, A.P.; Manju, V.S.; Raji, A.K. Use of biomedical plastic waste in bituminous road construction. Int. J. Eng.
Adv. Technol. 2014,3, 89–92.
17.
Raji, A.K.; Babu, K.K.; Sreekala, G. Utilisation of medical plastic wastes in bituminous pavement. In Proceedings of the XXI
Kerala Science Congress, Kollam, India, 19–21 August 2009; pp. 325–327.
18.
Tapkın, S. Mechanical evaluation of asphalt–aggregate mixtures prepared with fly ash as a filler replacement. Can. J. Civ. Eng.
2008,35, 27–40. [CrossRef]
19.
Warden, W.B.; Hudson, S.B.; Howell, H.C. Evaluation of mineral fillers in terms of practical pavement performance. Proc. Assoc.
Asph. Paving Technol. 1952,27, 101–110.
20. Sankaran, K.S. The influence of the quality of filler in asphaltic paving mixtures. J. Indian Roads Congr. 1973,35, 141–151.
21.
Henning, N.E. Evaluation of Lignite Fly Ash as a Mineral Filler in Asphaltic Concrete; Twin City Testing and Engineering Laboratory,
Inc.: St. Paul, MN, USA, 1974.
22. Mistry, R.; Roy, T.K. Effect of using fly ash as alternative filler in hot mix asphalt. Perspect. Sci. 2016,8, 307–309. [CrossRef]
23.
Anderson, D.A.; Bahia, H.U.; Dongre, R. Rheological Properties of Mineral Filler-Asphalt Mastics and Its Importance to Pavement
Performance; ASTM International: West Conshohocken, PA, USA, 1992.
24.
Zulkati, A.; Diew, W.Y.; Delai, D.S. Effects of Fillers on Properties of Asphalt-Concrete Mixture. J. Transp. Eng.
2012
,138, 902–910.
[CrossRef]
25.
Anderson, D.A.; Le Hir, Y.M.; Marasteanu, M.O.; Planche, J.-P.; Martin, D.; Gauthier, G. Evaluation of Fatigue Criteria for Asphalt
Binders. Transp. Res. Rec. J. Transp. Res. Board 2001,1766, 48–56. [CrossRef]
26.
Wang, H.; Al-Qadi, I.L.; Faheem, A.F.; Bahia, H.U.; Yang, S.-H.; Reinke, G.H. Effect of Mineral Filler Characteristics on Asphalt
Mastic and Mixture Rutting Potential. Transp. Res. Rec. J. Transp. Res. Board 2011,2208, 33–39. [CrossRef]
27.
Diab, A.; Enieb, M. Investigating influence of mineral filler at asphalt mixture and mastic scales. Int. J. Pavement Res. Technol.
2018,11, 213–224. [CrossRef]
28.
Rajitha, K.R.; Koramutla, T. Effect of Fillers on Bituminous Paving Mixes. Int. J. Eng. Res. Technol.
2019
,8, 2391–2397. [CrossRef]
29.
Mishra, B.; Gupta, M.K. Use of fly ash plastic waste composite in bituminous concrete mixes of flexible pavement. Am. J. Eng. Res.
2017,6, 253–262.
30.
Joshi, A.R.; Patel, S. Investigation into Sustainable Application of Class C Fly Ash Layer in Flexible Pavement. J. Hazard. Toxic
Radioact. Waste 2023,27, 04022033. [CrossRef]
31.
Mirkovi´c, K.; Toši´c, N.; Mladenovi´c, G. Effect of Different Types of Fly Ash on Properties of Asphalt Mixtures. Adv. Civ. Eng.
2019
,
2019, 1–11. [CrossRef]
32. Al Nageim, H.; Dulaimi, A.; Al-Busaltan, S.; Kadhim, M.A.; Al-Khuzaie, A.; Seton, L.; Croft, J.; Drake, J. The development of an
eco-friendly cold mix asphalt using wastewater sludge ash. J. Environ. Manag. 2023,329, 117015. [CrossRef]
33.
Suryani, F.M.; Yusuf, I.; Aida, H.; Farhan, A. Coal Ash Utilization as a Filler in Flexible Pavement Construction. In International
Conference on Experimental and Computational Mechanics in Engineering; Springer: Singapore, 2023; pp. 215–223.
34.
Joumblat, R.A.; Masri, Z.A.B.A.; Absi, J.; ElKordi, A. Investigation of using municipal solid waste incineration fly ash as alternative
aggregates replacement in hot mix asphalt. Road Mater. Pavement Des. 2022,24, 1290–1309. [CrossRef]
35.
Dahim, M.; Abuaddous, M.; Al-Mattarneh, H.; Rawashdeh, A.; Ismail, R. Enhancement of road pavement material using
conventional and nano-crude oil fly ash. Appl. Nanosci. 2021,11, 2517–2524. [CrossRef]
36.
Sobolev, K.; Vivian, I.F.; Saha, R.; Wasiuddin, N.M.W.; Saltibus, N.E. The effect of fly ash on the rheological properties of
bituminous materials. Fuel 2014,116, 471–477. [CrossRef]
37.
Al-Hdabi, A. Laboratory investigation on the properties of asphalt concrete mixture with Rice Husk Ash as filler. Constr. Build.
Mater. 2016,126, 544–551. [CrossRef]
38.
Radwan, A.A.M.; Satar, M.K.I.M.; Hassan, N.A.; Rogo, K.U. The Influence of Coal Fly Ash on the Mechanical Properties of Hot
Mix Asphalt Mixture. IOP Conf. Ser. Earth Environ. Sci. 2022,971, 012012. [CrossRef]
39.
Zhao, X.; Ge, D.; Wang, J.; Wu, D.; Liu, J. The Performance Evaluation of Asphalt Mortar and Asphalt Mixture Containing
Municipal Solid Waste Incineration Fly Ash. Materials 2022,15, 1387. [CrossRef]
40.
Joumblat, R.; Masri, Z.A.B.A.; Elkordi, A. Dynamic Modulus and Phase Angle of Asphalt Concrete Mixtures Containing Municipal
Solid Waste Incinerated Fly Ash as Mineral Filler Substitution. Int. J. Pavement Res. Technol. 2022, 1–21. [CrossRef]
41.
Joumblat, R.; Elkordi, A.; Khatib, J.; Masri, Z.A.B.A.; Absi, J. Characterisation of asphalt concrete mixes with municipal solid
waste incineration fly ash used as fine aggregates substitution. Int. J. Pavement Eng. 2022, 1–12. [CrossRef]
42.
Lu, Y.; Tian, A.; Zhang, J.; Tang, Y.; Shi, P.; Tang, Q.; Huang, Y. Physical and Chemical Properties, Pretreatment, and Recycling of
Municipal Solid Waste Incineration Fly Ash and Bottom Ash for Highway Engineering: A Literature Review. Adv. Civ. Eng.
2020
,
2020, 1–17.
43.
Yan, K.; Li, L.; Zheng, K.; Ge, D. Research on properties of bitumen mortar containing municipal solid waste incineration fly ash.
Constr. Build. Mater. 2019,218, 657–666. [CrossRef]
Materials 2023,16, 5612 17 of 18
44.
Jaber, S.K.; Aljawad, A.A.; Pop, E.; Prisecaru, T.; Pisa, I. The use of bottom ash and fly ash from medical incinerators as road
construction material. Sci. Bull. Univ. Politeh. Buchar. 2022,84, 2.
45.
ASTM-D3515-01; Standard Specification for Hot-Mixed, Hot-Laid Bituminous Paving Mixtures. ASTM International: West
Conshohocken, PA, USA, 2001.
46.
Tang, Q.; Liu, Y.; Gu, F.; Zhou, T. Solidification/Stabilization of Fly Ash from a Municipal Solid Waste Incineration Facility Using
Portland Cement. Adv. Mater. Sci. Eng. 2016,2016, 1–10. [CrossRef]
47.
ASTM D242; Standard Specification for Mineral Filler For Bituminous Paving Mixtures. ASTM International: West Conshohocken,
PA, USA, 2014.
48.
ASTM C618-19; Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete. ASTM
International: West Conshohocken, PA, USA, 2019.
49.
Chen, Y.; Xu, S.; Tebaldi, G.; Romeo, E. Role of mineral filler in asphalt mixture. Road Mater. Pavement Des.
2020
,23, 247–286.
[CrossRef]
50. ASTM C188-16; Standard Test Method for Density of Hydraulic Cement. ASTM International: West Conshohocken, PA, USA, 2016.
51.
ASTM D854-02; Standard Test Methods for Specific Gravity of Soil Solids by Water Pycnometer. ASTM International: West
Conshohocken, PA, USA, 2002.
52.
ASTM D6926-20; Standard Practice for Preparation of Asphalt Mixture Specimens Using Marshall Apparatus. ASTM International:
West Conshohocken, PA, USA, 2020.
53.
ASTM D1559; Test Method for Resistance of Plastic Flow of Bituminous Mixtures Using Marshall Apparatus. ASTM International:
West Conshohocken, PA, USA, 1989.
54.
ASTM D6927-15; Standard Test Method for Marshall Stability and Flow of Asphalt Mixtures. ASTM International: West
Conshohocken, PA, USA, 2015.
55.
Akbulut, H.; Gürer, C.; Çetin, S.; Elmacı, A. Investigation of using granite sludge as filler in bituminous hot mixtures. Constr.
Build. Mater. 2012,36, 430–436. [CrossRef]
56.
Mehari, Z.B. Effect of Different Types of Filler Materials on Characteristics of Hot-Mix-Asphalt Concrete; Addis Ababa University: Addis
Ababa, Ethiopia, 2007.
57.
USEPA 1311; Toxicity Characteristic Leaching Procedure. United States Environmental Protection Agency: Washington, DC, USA, 1992.
58.
NEN 7345; Leaching Characteristics of Solid Earthy and Stony Building and Waste Materials—Leaching Tests—Determination
of the Leaching of Inorganic Components from Buildings and Monolitic Waste Materials with the Diffusion Test. Nederlands
Normalisatie Instituut: Delft, The Netherlands, 1995.
59.
Malviya, R.; Chaudhary, R. Evaluation of leaching characteristics and environmental compatibility of solidified/stabilized
industrial waste. J. Mater. Cycles Waste Manag. 2006,8, 78–87. [CrossRef]
60.
Juel, A.I.; Mizan, A.; Ahmed, T. Sustainable use of tannery sludge in brick manufacturing in Bangladesh. Waste Manag.
2017
,60,
259–269. [CrossRef] [PubMed]
61. Kar, D.; Panda, M.; Giri, J.P. Influence of fly ash as a filler in bituminous mixes. ARPN J. Eng. Appl. Sci. 2014,9, 895–900.
62.
Rahman, A.; Ali, S.A.; Adhikary, S.K.; Hossain, Q.S. Effect of fillers on bituminous paving mixes: An experimental study. J. Eng.
Sci. 2012,3, 121–127.
63.
Mazumdar, M.; Rao, S.K. Effect of fly ash on engineering properties of sand-asphalt-sulfur paving mixes. Transp. Res. Rec.
1993
,
1993, 144.
64.
Jony, H.H.; Al-Rubaie, M.; Jahad, I. The effect of using glass powder filler on hot asphalt concrete mixtures properties.
Eng. Technol. J. 2011,29, 44–57.
65.
Sojobi, A.O.; Nwobodo, S.E.; Aladegboye, O.J. Recycling of polyethylene terephthalate (PET) plastic bottle wastes in bituminous
asphaltic concrete. Cogent Eng. 2016,3, 1133480. [CrossRef]
66.
Uzun, I.; Terzi, S. Evaluation of andesite waste as mineral filler in asphaltic concrete mixture. Constr. Build. Mater.
2012
,31,
284–288. [CrossRef]
67. Asphalt Institute. MS-2 Asphalt Mix Design Methods, 7th ed.; Asphalt Institute: Lexington, KY, USA, 2014.
68. Nayak, S.P. Characterization of bituminous concrete using flyash as filler. Gedrag Organ. Rev. 2020,33, 1326–1333. [CrossRef]
69.
Akter, R.; Hossain, M.K. Influence of rice husk ash and slag as fillers in asphalt concrete mixes. Am. J. Eng. Res.
2018
,6, 303–311.
70.
Chadbourn, B.A.; Skok, E.L., Jr.; Newcomb, D.E.; Crow, B.L.; Spindle, S. The Effect of Voids in Mineral Aggregate (VMA) on Hot-Mix
Asphalt Pavements; Minnesota Department of Transportation: Saint Paul, MN, USA, 1999.
71.
Sargın, ¸S.; Saltan, M.; Morova, N.; Serin, S.; Terzi, S. Evaluation of rice husk ash as filler in hot mix asphalt concrete. Constr. Build.
Mater. 2013,48, 390–397. [CrossRef]
72.
Carpenter, C.A. A Cooperative Study of Fillers in Asphaltic Concrete; Federal Highway Administration: Washington, DC, USA, 1952.
73.
Choudhary, J.; Kumar, B.; Gupta, A. Utilization of solid waste materials as alternative fillers in asphalt mixes: A review. Constr.
Build. Mater. 2020,234, 117271. [CrossRef]
74.
Kuity, A.; Jayaprakasan, S.; Das, A. Laboratory investigation on volume proportioning scheme of mineral fillers in asphalt mixture.
Constr. Build. Mater. 2014,68, 637–643. [CrossRef]
75.
Sai, G.M.; Datta, Y.S.; Lakshmayya, M.T.S. Effect of using pond ash as filler in bituminous mix. Int. J. Res. Anal. Rev.
2019
,6,
1492–1495.
Materials 2023,16, 5612 18 of 18
76.
Sharma, V.; Chandra, S.; Choudhary, R. Characterization of Fly Ash Bituminous Concrete Mixes. J. Mater. Civ. Eng.
2010
,22,
1209–1216. [CrossRef]
77.
Juel, M.A.I.; Chowdhury, Z.U.M.; Ahmed, T. Heavy metal speciation and toxicity characteristics of tannery sludge. In AIP
Conference Proceedings; AIP Publishing: Melville, NY, USA, 2016; p. 060009. [CrossRef]
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