sustainability

Article
Study on the Performances of Waste Crumb Rubber
Modified Asphalt Mixture with Eco-Friendly
Diatomite and Basalt Fiber
Wensheng Wang 1,2, * , Yongchun Cheng 1 , Heping Chen 2, *, Guojin Tan 1 , Zehua Lv 3
and Yunshuo Bai 1
1 College of Transportation, Jilin University, Changchun 130025, China; chengyc@jlu.edu.cn (Y.C.);
tgj@jlu.edu.cn (G.T.); baiys19@mails.jlu.edu.cn (Y.B.)
2 Ingram School of Engineering, Texas State University, San Marcos, TX 78666, USA
3 Hebei Provincial Communications Planning and Design Institute, Shijiazhuang 050000, China;
lvzh2019@163.com
* Correspondence: wangws17@mails.jlu.edu.cn (W.W.); hc15@txstate.edu (H.C.)




Received: 23 August 2019; Accepted: 24 September 2019; Published: 25 September 2019


Abstract: A sustainable and environmentally friendly society is developing rapidly, in which

pavement engineering is an essential part. Therefore, more attention has been paid toward waste
utilization and urban noise pollution in road construction. The object of this study was not only
to investigate the mix proportion of waste crumb modified asphalt mixtures with diatomite and
basalt fiber but also to evaluate the comprehensive performances including sound and vibration
absorption of modified asphalt mixtures. Firstly, the mix proportion scheme was designed based
on Marshall indices and sound and vibration absorption properties according to the orthogonal
experimental method. Considering the specification requirements, as well as better performances,
the optimal mix proportion was determined as follows: diatomite content at 7.5%, basalt fiber content
at 0.3%, and asphalt-aggregate ratio at 5.5%. The range and variance analysis results indicated that
asphalt-aggregate ratio has the most significant influence on volumetric parameters, diatomite has
the most significant influence on sound absorption, and basalt fiber has the most significant influence
on vibration reduction. Furthermore, the conventional pavement performances and sustainable
sound and vibration absorption performances of modified asphalt mixtures were also analyzed.
The results showed that the performances of modified asphalt mixtures were improved to different
extents compared to the base asphalt mixture. This may be attributed to the microporous structure
property of diatomite and the spatial network structure formed by basalt fibers. The pavement as
well as sound and vibration absorption performances of the waste crumb modified asphalt mixture
with diatomite and basalt fiber would be a good guidance for asphalt pavement design.

Keywords: asphalt mixture; diatomite; basalt fiber; orthogonal experiment; sound absorption;
vibration absorption

1. Introduction
Modern pavements not only need to satisfy the mechanical performances but they also need meet
the requirements of service performances in regard to security, smoothness, comfortable driving, and
environmental effects according to different traffic environments. Compared with cement concrete
pavement, asphalt pavement produces less road noise and is more comfortable to drive [1,2]. The
performance of asphalt pavement is still a hot and difficult point in the field of pavement engineering.
Nowadays, in order to improve the physical and mechanical properties of asphalt mixtures, adding
modifiers to asphalt has gradually become the focus of research and is a commonly used method [3,4].

Sustainability 2019, 11, 5282; doi:10.3390/su11195282 www.mdpi.com/journal/sustainability

Sustainability 2019, 11, 5282 2 of 15

Polymers are one kind of the widely adopted modifiers for asphalt, and much research has
been carried out on the addition of various polymers into asphalt [5–7]. Due to the urgent need for
waste recycling, crumb rubber as one early used modifier is widely used in asphalt to improve the
performances of asphalt mixtures [8,9]. Nowadays, there are many of end-of-life tires in the world
because of the rapid development of the vehicle industry. The end-of-life tires are considered a great
threat to the environment and to human beings, and it will be very helpful and beneficial if those
end-of-life tires are recycled as crumb rubber used for pavement engineering. La Rosa et al. [10] used
life cycle assessment to study the effect of styrene-isoprene-styrene by adding ground end-of-life
tire rubber. Peralta et al. [11] investigated the quantitative relationship between asphalt and rubber,
and the test results showed that the addition of rubber into asphalt would improve the physical and
rheological performances. Manosalvas-Paredes et al. [12] found that rubber modified stone mastic
asphalt had better moisture stability and resistance to permanent deformation. Based on a large
number of previous studies, crumb rubber has been proven as a very effective modifier for asphalt,
and it has many advantages such as high- and low-temperature anti-deformation, noise absorption,
moisture stability, and so on [13].
Fibers, such as glass fiber, corn stalk fiber, polyester, etc., are usually regarded as the skeleton
materials for asphalt and have been widely applied in asphalt pavement engineering [14–16]. Basalt
fiber is a kind of eco-friendly fiber additive with many excellent performances, such as high toughness
and good damping properties. Basalt fiber has been widely used in the field of aeronautics and in
ships for their sound absorption, insulation, and vibration reduction properties. [17]. Wang et al. [18]
studied the effect of basalt fiber on asphalt materials with the help of direct tension and fatigue tests,
and they found that the addition of basalt fiber could improve the low-temperature performance
of road materials to some extent. Gu et al. [19] found that asphalt materials reinforced with basalt
fiber has better high-temperature mechanical properties due to its superior mechanical and thermal
properties. Zhang et al. [20] adopted the numerical method and related software to investigate and
analyze the mechanical performance of asphalt mix modified by basalt fiber. They also discussed the
influences of basalt fiber content and aspect ratio on the mechanical performances of asphalt mix. Qin
et al. [21] studied the influences of basalt fiber contents and lengths on the pavement performances of
asphalt mixtures, and they concluded that the optimal basalt fiber length was 6 mm for the excellent
asphalt absorption.
Diatomite, as a kind of natural and eco-friendly inorganic modifier, can not only improve the
pavement performances of asphalt mixtures but it also has the characteristics of strong adsorption
performance and high micro-porosity. This is because diatomite is a sedimentary rock composed
of fossilized skeletons of diatoms, which forms a honeycomb silica structure and results in a higher
specific surface area [22]. It has been widely used in the construction industry for its performance in
sound absorption, air purification, and moisture removal [23]. Tan et al. [24] compared and analyzed
the low-temperature performances of asphalt mixtures with and without diatomite and found that
diatomite could improve the low-temperature performance. They also discussed the influence of
diatomite content. Guo et al. [14] also showed that diatomite could improve the low-temperature and
thermal mechanical properties of asphalt mixtures based on a large number of experiments. Yang
et al. [25] aimed to test the pavement performances of asphalt mixtures with diatomite content and
they found that diatomite was strongly correlated with the high-temperature properties and there was
little correlation between diatomite and the low-temperature properties. Bao [26] also investigated the
comprehensive road performances of asphalt mixtures with diatomite, and test results showed that the
modified asphalt mixture had better high-temperature and mechanical properties and water stability
compared to base asphalt mixtures.
With the development of modernization, noise has become a serious environmental problem
affecting human beings, animals, and plants. Relevant research shows that road traffic noise is one
of the main noise sources [27]. Low noise pavements are actually used as the best solution in order
to comply with mitigations and action plans demands [28–31]. According to current research on
Sustainability 2019, 11, 5282 3 of 15

basalt fiber and diatomite modified asphalt mixtures, many studies aimed to improve the conventional
pavement performances of asphalt mixture. However, less research has been carried out on the noise
investigation of pavement engineering. While dealing with pavement designs for noise reduction,
the acoustic performances of a road surface are due to both acoustic absorption and tire/road noise
generation [32]. Exciting research has shown that the impedance tube test has been proven as an
effective method to characterize the sound absorption property of materials [33]. Guo et al. [34] studied
the noise absorption and corresponding factors of porous asphalt mixtures and field asphalt pavements
by using the impedance tube method. They found that rubber, air void, and surface texture could
influence the noise absorption property of asphalt pavement. In addition, there are methods to evaluate
the vibration reduction property of pavement, including tire free vibration attenuation and pavement
hammering tests [35]. Thereafter, it is necessary to investigate the comprehensive performances,
including sound and vibration absorption of asphalt mixtures with diatomite and basalt fibers.
The main objective of this study was not only to investigate the mix proportion of diatomite and
basalt fiber composite modified asphalt mixtures but also to evaluate the comprehensive performances
including sound and vibration absorption of modified asphalt mixtures. Firstly, the mix proportion
scheme was designed based on the orthogonal experimental method. Then, the optimal mix proportion
was determined considering the specification requirements as well as better performances. Moreover,
the conventional pavement performances and sustainable sound and vibration absorption performances
of modified asphalt mixtures were also analyzed.

2. Experimental Materials and Methods

2.1. Experimental Materials

The experimental materials used in this study included waste crumb rubber modified asphalt,
aggregates, mineral filler, basalt fiber, as well as diatomite. The waste rubber modified asphalt was
made from base asphalt AH–90# and waste rubber, in which the technical properties of base asphalt
AH–90# from Liaoning Province are shown in Table 1, and the properties of waste crumb rubber with
a maximum particle size of 550 µm from Jilin Province are shown in Table 2. The technical properties
of course and fine aggregates as well as mineral filler from Jiutai, Jilin Province, are listed in Tables 3–5,
respectively. The basalt fiber with a length of 6 mm was chosen for the asphalt mixtures in this study.
The appearance of basalt fiber is golden brown, and basalt fibers have good mechanical properties,
low water absorption, and a high melting point. The detailed technical properties have been given in
previous studies [2,21]. The properties of diatomite have been introduced in a previous study [36].
The above physical properties meet the requirement of the specifications JTG F40–2004.

Table 1. Technical properties of base asphalt AH–90#.

Test Items Standards Requirements Values

Penetration 0.1 mm (@ 25 ◦ C, 100 g, 5 s) T0604 80~100 86
Ductility cm (@ 15 ◦ C, 5 cm/min) T0605 ≥100 135
Softening point ◦C T0606 ≥44 44.5
Density g/cm3 T0603 — 1.052
RTFOT
Mass loss % T0609 ±0.8 0.06
Penetration ratio % (@ 25 ◦ C) T0609 ≥57 66.3
Sustainability 2019, 11, 5282 4 of 15

Table 2. Technical properties of waste crumb rubber.

Test Items Requirements Values

Apparent Density (g/cm3 ) 1.1~1.3 1.18
Moisture Content (%) <1 0.32
Metal Content (%) <0.05 0.038
Fiber Content (%) <1 0.43
Carbon Black Content (%) ≥28 39.6
Rubber Hydrocarbon Content (%) ≥42 51

Table 3. Technical properties of basalt coarse aggregates.

Test Items Requirements Values

Crushing Value % ≤26 10.1
Los Angeles Abrasion Value % ≤28 16.4
13.2 mm 2.821
Apparent Specific Gravity 9.5 mm — ≥2.6 2.796
4.75 mm 2.718
13.2 mm 0.6
Water Absorption 9.5 mm % ≤2.0 0.29
4.75 mm 0.8
Soundness % ≤12 9
Elongated Particle Content % ≤15 7.3
Passing 0.075 mm Sieve % ≤1 0.3

Table 4. Technical properties of basalt fine aggregates.

Test Items Requirements Values

Apparent Specific Gravity ≥2.5 2.725
Water Absorption (%) — 0.63
Angularity (s) ≥30 40.2
Sand Equivalent (%) ≥60 72.3

Table 5. Technical properties of limestone mineral filler.

Test Items Requirements Values

Apparent Density (g/cm3 ) ≥2.5 2.707
Hydrophilic Coefficient <1 0.6
Water Content (%) ≤1 0.4
Plastic Index (%) <4 2
<0.6 mm 100 100
Granular Composition (%) <0.15 mm 90~100 91.4
<0.075 mm 75~100 72.9

2.2. Mix Design and Specimen Preparations

The gradation of AC-13 (which is usually used in the upper layers of highways), as illustrated
in Figure 1, was selected for the asphalt mixtures in this study. For the mix design, the orthogonal
experimental design and the Marshall design were combined to study the diatomite and basalt fiber
composite modified asphalt mixtures. The diatomite content, basalt fiber content, and asphalt-aggregate
ratio were chosen as the orthogonal factors. The L9 orthogonal table was used to design the three-factor
experiment, and the mix design of composite modified asphalt mixtures is shown in Table 6. The
mentioned AC specimens with diatomite and basalt fiber were prepared by the Marshall compaction
method. The detailed procedures have been illustrated in previous studies [16,30].
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100
90 Upper limit
80
Lower limit

Cumulative passing/%
Selected gradation
70
60
50
40
30
20
10
0
9.5

0.6

0.3
2

75
16

4.7

2.3

1.1

0.1
13.

0.0
Mesh size/mm

Figure 1. Gradation of AC-13.

Figure 1. Gradation of AC-13.
Table 6. Mix orthogonal design of diatomite and basalt fiber composite modified asphalt mixture.
Table 6. Mix orthogonal design of diatomite and basalt fiber composite modified asphalt mixture.
Basalt Fiber Content Asphalt-Aggregate
GroupDiatomite
Group No. No. Diatomite
Content Content
(%) (%)Basalt Fiber Content
(%) (%) Asphalt-Aggregate
Ratio (%) Ratio (%)
1 1 5 (L1) 5 (L1) 0.2 (L1)
0.2 (L1) 5.05.0 (L1)
(L1)
2 2 5 (L1) 5 (L1) 0.3 (L2)
0.3 (L2) 5.55.5 (L2)
(L2)
3 3 5 (L1) 5 (L1) 0.4 (L3)
0.4 (L3) 6.06.0
(L3)
(L3)
4 4 7.5 (L2)7.5 (L2) 0.2 (L1)
0.2 (L1) 5.55.5
(L2)
(L2)
5 7.5 (L2) 0.3 (L2) 6.0 (L3)
5 7.5 (L2) 0.3 (L2) 6.0 (L3)
6 7.5 (L2) 0.4 (L3) 5.0 (L1)
6 7 7.5 (L2)10 (L3) 0.4 (L3)
0.2 (L1) 6.05.0 (L1)
(L3)
7 8 10 (L3) 10 (L3) 0.2 (L1)
0.3 (L2) 5.06.0 (L3)
(L1)
8 9 10 (L3) 10 (L3) 0.4 (L3)
0.3 (L2) 5.55.0
(L2)
(L1)
9 10 (L3) 0.4 (L3) 5.5 (L2)
2.3. Experimental Methods
2.3. Experimental Methods
2.3.1. Design Indices of Orthogonal Experiment
2.3.1. Design Indices of Orthogonal Experiment
Marshall Design Indices
Marshall Design Indices
The volumetric properties of the Marshall design method will directly influence the performances
of asphalt mixtures. In properties
The volumetric the study, air
ofvoids
the (VA), voidsdesign
Marshall in mineral aggregates
method will (VMA),
directlyand voids filled
influence the
with asphalt (VFA), as well as Marshall stability (MS) and flow (FL), were adopted as
performances of asphalt mixtures. In the study, air voids (VA), voids in mineral aggregatesthe dependent
(VMA),
variables
and voidsoffilled
orthogonal experiments.
with asphalt (VFA), asThese
well Marshall design
as Marshall indices
stability have
(MS) andbeen
flowdefined in previous
(FL), were adopted
studies [16,31].
as the dependent variables of orthogonal experiments. These Marshall design indices have been
defined in previous studies [16,31].
Sound and Vibration Absorption Properties
Sound and Vibration
Effective methodsAbsorption Properties
for characterizing the sound absorption property of materials mainly include
the reverberation chamber method and the impedance tube method, and the reverberation chamber
Effective methods for characterizing the sound absorption property of materials mainly include
method is relatively expensive. The impedance tube method has low requirements for specimens and
the reverberation chamber method and the impedance tube method, and the reverberation chamber
is precise and convenient while measuring the sound absorption properties of specimens [28]. The
method is relatively expensive. The impedance tube method has low requirements for specimens and
measurement system using the impedance tube method is shown in Figure 2a; it consists of a power
is precise and convenient while measuring the sound absorption properties of specimens [28]. The
amplifier, loudspeaker, impedance tube, microphone, and data acquisition system. The specimen was
measurement system using the impedance tube method is shown in Figure 2a; it consists of a power
firstly placed on one side of impedance tube, and the loudspeaker was placed on the other side to
amplifier, loudspeaker, impedance tube, microphone, and data acquisition system. The specimen
was firstly placed on one side of impedance tube, and the loudspeaker was placed on the other side
 |Pmin| = P0 × (1  |r|), (2)

G = |Pmax|/|Pmin| = (1 + |r|)/(1  |r|), (3)

α = 1  |r|2 = 4 × G/(G + 1)2, (4)

Sustainability 2019, 11, 5282 6 of 15
where P0 is the acoustic amplitude of loudspeaker; r is the reflective defined by the ratio of reflected
wave Pr and acoustic wave Pi; Pmax and Pmin are obtained when Pr and Pi are in phase or out of phase,
produce an acoustic wave. Then, the sound absorption properties of materials could be measured
respectively; G is the standing wave ratio; and α is the sound absorption coefficient.
through the standing wave ratio, which could be calculated by Equations (1–4).
According to the ASTM C423–09a standard, the sound absorption average (SAA) is a single
number rating—the average, rounded off to the nearest 0.01, of the sound absorption coefficients of
|Pmax | = P0 × (1 + |r|), (1)
a material for the twelve one-third octave bands from 200 through 2500 Hz, inclusive, measured
according to this method. |Pmin | = P0 × (1 − |r|), (2)
In this study, the tire free vibration attenuation test was selected to evaluate the vibration
G = |Pmax
absorption property of modified asphalt |/|Pmin | and
mixture, = (1 the
+ |r|)/(1 − |r|), of tire free vibration attenuation
schematic (3)
test is shown in Figure 2b. The damping α = 1ratio
− |r|2(DR)
= 4 ×isG/(G
defined
+ 1)2in
, the Equation (5) and was adopted (4)
for evaluating the damping vibration reduction property.
where P0 is the acoustic amplitude of loudspeaker; r is the reflective defined by the ratio of reflected
wave Pr and acoustic wave Pi ; Pmax and Pminζ are = δ/(4π 2
+δ2)1/2when
obtained , (5)
Pr and Pi are in phase or out of phase,
where ζ is theGdamping
respectively; is the standing wave
ratio and δ isratio; and α is theattenuation
the logarithmic sound absorption
rate. coefficient.

Data acquisition
Power amplifier
PC

Microphone Piston

Loudspeaker Impedence tube Specimen

(a)
Tyre
Accelerometer

Dynamic
measurement
PC system
Slab specimen
(b)
Figure
Figure 2.
2. Schematic
Schematicof
ofsound
soundand
andvibration
vibrationabsorption:
absorption: (a)
(a)impedance
impedancetube;
tube;(b)
(b)tire
tirefree
free vibration.
vibration.

According to the ASTM C423–09a standard, the sound absorption average (SAA) is a single
number rating—the average, rounded off to the nearest 0.01, of the sound absorption coefficients
of a material for the twelve one-third octave bands from 200 through 2500 Hz, inclusive, measured
according to this method.
In this study, the tire free vibration attenuation test was selected to evaluate the vibration absorption
property of modified asphalt mixture, and the schematic of tire free vibration attenuation test is shown
Sustainability 2019, 11, 5282 7 of 15

in Figure 2b. The damping ratio (DR) is defined in the Equation (5) and was adopted for evaluating
the damping vibration reduction property.

ζ = δ/(4π2 +δ2 )1/2 , (5)

where ζ is the damping ratio and δ is the logarithmic attenuation rate.

2.3.2. Pavement Performances for Asphalt Mixtures

Based on the optimal mix proportion of diatomite and basalt fiber composite modified asphalt
mixtures, the pavement performance tests were carried out to evaluate the diatomite and basalt
fiber composite modified asphalt mixtures, which focused on the high-temperature rutting test,
low-temperature splitting test, moisture stability (immersion Marshall and freeze-thaw splitting), as
well as sound and vibration absorption tests. The specific experimental processes and steps can be
found for the high-temperature rutting test, low-temperature splitting test, and moisture stability in
previous studies [37,38].

3. Results and Discussion

For each orthogonal group, six Marshall specimens were used for Marshall design indices and
the sound absorption test, and three slab specimens were used for the vibration absorption test. The
orthogonal experimental results (i.e., Marshall design indices and sound and vibration absorption) of
diatomite and basalt fiber composite modified asphalt mixtures are summarized in Table 7.

Table 7. Orthogonal results of diatomite and basalt fiber composite modified asphalt mixtures.

Group No. VA (%) VMA (%) VFA (%) MS (kN) FL (mm) SAA DR
1 4.6 14.8 69.2 13.70 3.69 0.090 0.03854
2 3.7 15.1 75.5 14.31 3.43 0.100 0.04209
3 3.4 15.9 78.7 13.82 3.63 0.098 0.05150
4 3.6 15.0 76.3 14.56 3.18 0.106 0.04324
5 3.5 15.9 78.0 14.17 3.32 0.102 0.05117
6 5.0 15.3 67.1 14.16 3.38 0.111 0.05123
7 3.4 15.9 78.6 13.58 3.56 0.114 0.05222
8 4.8 15.0 68.4 14.20 3.31 0.118 0.04427
9 4.9 16.1 69.6 14.36 3.07 0.157 0.05481
Note: VA—air voids, VMA—voids in mineral aggregates, VFA—voids filled with asphalt, MS—Marshall stability,
FL—flow, SAA—sound absorption average, DR—damping ratio.

3.1. Analysis of Orthogonal Experimental Design for Composite Modified Asphalt Mixtures

3.1.1. Range Analysis

In this study, the range method was used to calculate the range (R) of each index, and the
relationship trend between design indices and factor levels was plotted for the orthogonal experiment
to determine the order and the optimal mix proportion of the three factors, i.e., the diatomite content,
basalt fiber content, and asphalt-aggregate ratio. The range analysis results are shown in Figure 3,
in which L1, L2, and L3 represent three levels of the orthogonal factors and R is the range value of
different orthogonal factors. A larger R value indicates the corresponding orthogonal factor has a
greater influence on the design index.
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5.0 16.0

4.5

R=0.533
R=0.400

R=0.867
15.5

R=1.367
R=0.567
R=0.467

VMA (%)
VA (%)

4.0

15.0
3.5 Diatomite content (%) Diatomite content (%)
Basalt fiber content (%) Basalt fiber content (%)
Asphalt-aggregate ratio (%) Asphalt-aggregate ratio (%)
3.0 14.5
L1 L2 L3 L1 L2 L3
Orthogonal factor level Orthogonal factor level

(a) (b)
80 Diatomite content (%) 14.6 Diatomite content (%)
Basalt fiber content (%) 14.5 Basalt fiber content (%)
78
Asphalt-aggregate ratio (%) Asphalt-aggregate ratio (%)
14.4
76
14.3
VFA (%)

MS (kN)
R=10.200
R=2.267
R=2.900

74 14.2

R=0.353
R=0.553
R=0.280
14.1
72
14.0
70
13.9

68 13.8
L1 L2 L3 L1 L2 L3
Orthogonal factor level Orthogonal factor level

(c) (d)
4.0 Diatomite content (%) 0.14 Diatomite content (%)
Basalt fiber content (%) Basalt fiber content (%)
3.8 Asphalt-aggregate ratio (%) 0.13 Asphalt-aggregate ratio (%)

3.6 0.12
FL (mm)

SAA

R=0.033
R=0.018
R=0.017
R=0.123

R=0.277
R=0.290

3.4 0.11

3.2 0.10

3.0 0.09
L1 L2 L3 L1 L2 L3
Orthogonal factor level Orthogonal factor level

(e) (f)

Figure 3. Cont.
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Sustainability 2019, 11, x FOR PEER REVIEW 10 of 16

0.054 Diatomite content (%)

Basalt fiber content (%)
0.052 Asphalt-aggregate ratio (%)

0.050

R=0.008
R=0.007
DR

R=0.006
0.048

0.046

0.044

0.042
L1 L2 L3
Orthogonal factor level
(g)
Figure
Figure 3.
3. Relationships
Relationshipsbetween
betweendesign
designindices and
indices factor
and levels
factor for for
levels the the
orthogonal experiment:
orthogonal (a)
experiment:
VA—air voids;
(a) VA—air (b) VMA—voids
voids; (b) VMA—voids in mineral aggregates;
in mineral (c) VFA—voids
aggregates; filled with
(c) VFA—voids asphalt;
filled with(d) MS—
asphalt;
Marshall stability;stability;
(d) MS—Marshall (e) FL—flow; (f) SAA—sound
(e) FL—flow; (f) SAA—soundabsorption coefficient;
absorption and
coefficient; and(g)
(g)DR—vibrations
DR—vibrations
absorption
absorption coefficient.

Air Voids
3.1.2. (VA) Analysis
Variance
According
The to Figuremethod
range analysis 3a, withdoes
different levels ofthe
not consider theinfluence
orthogonal of factors,
errors on VAorder
thethe valuesofof diatomite
orthogonal
factors and cannot quantitatively analyze the importance of each orthogonal factor. Therefore,order
and basalt fiber composite modified asphalt mixtures met the standard of 3.0–5.0%. The influence the
of three orthogonal
variance analysis method on VA
factors was wastoasphalt-aggregate
used accurately analyze the>significance
ratio of each >
basalt fiber content diatomite content.
orthogonal factor.
The increase of asphalt
The variance content
analysis would
results fill the voids
of diatomite in thefiber
and basalt asphalt mixture,
composite leadingasphalt
modified to a decrease
mixturesin
the V A. Due to the adsorption of asphalt by diatomite and basalt
are listed in Table 8. From Table 8, the following conclusions can be drawn: fibers, the increase of diatomite and
basalt fiber content would absorb more asphalt, reduce free asphalt, and then increase the VA. At the
(a)
sameThe F-value
time, indicates
the spatial the significance
network structure madeof different orthogonal
by basalt factors
fibers would on the the
enhance design indices,
asphalt and
mixture,
the significances of three orthogonal factors on these design indices were consistent
resulting in difficulties in compacting asphalt mixtures. Therefore, the addition of basalt fibers would with the
influencethe
also increase order in the range analysis.
VA gradually.
(b) The F-values of the asphalt-aggregate ratios for VA, VMA, VFA, and MS were larger than those
Voidsofindiatomite and basalt fiber
Mineral Aggregates (VMA) content, which indicates that the influences of asphalt-aggregate
ratio were larger than the others on VA, VMA, VFA, and MS. The F-value of the asphalt-
From Figure 3b, with different levels of the orthogonal factors, the VMA values of diatomite and
aggregate ratio on VA was larger than F0.1, which represents a 90% probability that the asphalt-
basalt fiber composite modified asphalt mixtures met the standard of >14.0%. The influence order of
aggregate ratio had a significant influence. The F-value of asphalt-aggregate ratio on VMA was
three orthogonal factors on VMA is asphalt-aggregate ratio > basalt fiber content > diatomite content.
larger than F0.2, which represents a 80% probability that asphalt-aggregate ratio had a significant
The increase of the asphalt-aggregate ratio, basalt fibers, and diatomite content would increase the
influence. The F-value of the asphalt-aggregate ratio on VFA was larger than F0.05, which
VMA value of asphalt mixtures. This is because the excessive amount of asphalt would gradually
represents a 95% probability that the asphalt-aggregate ratio had a significant influence.
expand the mineral aggregates, resulting in an increase of the voids in mineral aggregates (VMA).
(c) For the sound absorption property, the F-value of diatomite was the largest, the F-value of basalt
Voidsfiber was
Filled smaller
with than
Asphalt diatomite, and asphalt-aggregate ratio was lightly smaller than basalt
(VFA)
fiber. This means that diatomite had a more significant influence on SAA compared with basalt
Figure
fiber and3c the
shows that the influence
asphalt-aggregate order of three orthogonal factors on VFA was asphalt-aggregate
ratio.
ratio > basalt fiber content > diatomite
(d) For the vibration absorption property, content. Because
the F-value of thefiber
of basalt absorption
was theoflargest,
asphalttheof F-value
diatomiteof
and basalt fibers, with the
asphalt-aggregate ratioincrease of their
was smaller content,
than basaltthe VFAand
fiber, of the asphalt was
diatomite mixture would
slightly gradually
smaller than
decrease. Compared with diatomite,
the asphalt-aggregate ratio. Thisbasalt
meansfiber
thathad a greater
basalt fiber hadimpact the VFA. influence on DR
on significant
a more
compared with diatomite and the asphalt-aggregate ratio.
Marshall Stability (MS) and Flow (FL)
Figure 3d indicates that the influence
Table 8. Variance order
analysis for of threeresults
orthogonal orthogonal factors
of modified on MSmixture.
asphalt was asphalt-aggregate
ratio > diatomite content > basalt fiber content. Meanwhile, Figure 3e indicates that the influence order
Factor Diatomite (%) Basalt Fiber (%) Asphalt-Aggregate Ratio (%)
of three orthogonal factors on FL was diatomite content > asphalt-aggregate ratio > basalt fiber content.
F-value 1.333 2.026 10.795
VAthe increase of the asphalt-aggregate ratio, basalt fibers, and diatomite content, the MS values
With
Significance — — **
would firstly increase and then decrease, while the FL values would firstly decrease and then increase.
F-value 1.836 3.557 8.377
Diatomite
VMA can enhance the adhesion of asphalt mortar, while excessive diatomite would affect the
Significance — — *
VFA F-value 1.081 1.812 20.786
Sustainability 2019, 11, 5282 10 of 15

adhesion between asphalt binder and aggregate, decreasing the stability of asphalt mixtures. Basalt
fibers would form a spatial network structure, thus improving the stability; excessive basalt fibers
would agglomerate, reducing the stability of the network structure and making the stability decline.

Sound Absorption Coefficient (SAA)

It can be seen from Figure 3f that the influence order of three orthogonal factors on SAA was
diatomite content > basalt fiber content > asphalt-aggregate ratio. With the increase of diatomite and
basalt fiber content, the SAA of composite modified asphalt mixtures showed an increasing trend. The
larger the diatomite and basalt fiber content, the better the sound absorption ability of the asphalt
mixture. This is because the microporous structure of diatomite has an excellent sound absorption
effect, and the addition of basalt fibers forming the network structure plays a role in the loss of sound
energy, so the sound absorption coefficient becomes larger.

Vibration Absorption Coefficient (DR)

It can be seen from Figure 3g that the influence order of three orthogonal factors on DR is basalt
fiber content > asphalt-aggregate ratio > diatomite content. The increase of diatomite, basalt fibers,
and asphalt would increase the damping ratio of the asphalt mixture. The addition of basalt fiber had
the best effect on the vibration reduction. The special network structure by basalt fibers will strength
and enhance asphalt mixtures, leading to a better vibration reduction performance.

3.1.2. Variance Analysis

The range analysis method does not consider the influence of errors on the order of orthogonal
factors and cannot quantitatively analyze the importance of each orthogonal factor. Therefore, the
variance analysis method was used to accurately analyze the significance of each orthogonal factor.
The variance analysis results of diatomite and basalt fiber composite modified asphalt mixtures
are listed in Table 8. From Table 8, the following conclusions can be drawn:

(a) The F-value indicates the significance of different orthogonal factors on the design indices, and
the significances of three orthogonal factors on these design indices were consistent with the
influence order in the range analysis.
(b) The F-values of the asphalt-aggregate ratios for VA, VMA, VFA, and MS were larger than those
of diatomite and basalt fiber content, which indicates that the influences of asphalt-aggregate
ratio were larger than the others on VA, VMA, VFA, and MS. The F-value of the asphalt-aggregate
ratio on VA was larger than F0.1 , which represents a 90% probability that the asphalt-aggregate
ratio had a significant influence. The F-value of asphalt-aggregate ratio on VMA was larger than
F0.2 , which represents a 80% probability that asphalt-aggregate ratio had a significant influence.
The F-value of the asphalt-aggregate ratio on VFA was larger than F0.05 , which represents a 95%
probability that the asphalt-aggregate ratio had a significant influence.
(c) For the sound absorption property, the F-value of diatomite was the largest, the F-value of basalt
fiber was smaller than diatomite, and asphalt-aggregate ratio was lightly smaller than basalt fiber.
This means that diatomite had a more significant influence on SAA compared with basalt fiber
and the asphalt-aggregate ratio.
(d) For the vibration absorption property, the F-value of basalt fiber was the largest, the F-value of
asphalt-aggregate ratio was smaller than basalt fiber, and diatomite was slightly smaller than
the asphalt-aggregate ratio. This means that basalt fiber had a more significant influence on DR
compared with diatomite and the asphalt-aggregate ratio.
Sustainability 2019, 11, 5282 11 of 15

Table 8. Variance analysis for orthogonal results of modified asphalt mixture.

Factor Diatomite (%) Basalt Fiber (%) Asphalt-Aggregate Ratio (%)

F-value 1.333 2.026 10.795
VA
Significance — — **
F-value 1.836 3.557 8.377
VMA
Significance — — *
F-value 1.081 1.812 20.786
VFA
Significance — — ***
F-value 4.089 2.458 10.015
MS
Significance * — **
F-value 9.559 1.753 8.069
FL
Significance ** — *
F-value 11.023 3.608 3.056
SAA
Significance ** — —
F-value 7.857 13.051 9.301
DR
Significance — ** **
Note: * is significant at 0.2 level, ** is significant at 0.1 level, *** is significant at 0.05 level, F0.2 = 4, F0.1 = 9, F0.05 = 19.

3.2. Pavement Performances and of Diatomite and Basalt Fiber Composite Modified Asphalt Mixtures
Based on the range analysis and variance analysis, different orthogonal factors had different
influences and significances on the orthogonal design indices. Considering the specification
requirements as well as better performances of modified asphalt mixture, the optimal mix proportion
in the orthogonal experiment was determined as follows: diatomite content at 7.5%, basalt fiber content
at 0.3%, and asphalt-aggregate ratio at 5.5%. The corresponding Marshall indices were as follows:
VA = 3.9%, VMA = 15.2%, VFA = 74.4%, MS = 15.74 kN, FL = 3.85 mm. For the comparison and
illustration of the performances of the diatomite and basalt fiber composite modified asphalt mixture,
the base asphalt mixture was selected as the control group. The optimal asphalt-aggregate ratio of
the base asphalt mixture was 5.1%. The corresponding Marshall indices were as follows: VA = 3.6%,
VMA = 14.1%, VFA = 75%, MS = 14.28 kN, FL = 3.26 mm. Three replicate specimens of both the control
group and the experimental group were prepared for each performance test.
In order to further evaluate the improvement effect of composite modified asphalt mixtures on
pavement performances, sound and vibration absorption performances, high-temperature rutting,
low-temperature splitting, moisture stability, impedance tube, and tire free vibration tests were
conducted, and the comparison results are plotted in Figures 4 and 5. As shown in Figure 4a, compared
with the base asphalt mixture, the dynamic stability of diatomite and basalt fiber composite modified
asphalt mixture was greatly improved, and its high-temperature rutting resistance was improved by
66.7%. This is because diatomite enhances the adhesion between asphalt mortar and aggregate, and
the special network structure of basalt fibers reduces the mobility of asphalt and then improves the
high-temperature rutting resistance. Meanwhile, Figure 4a shows that the low-temperature cracking
energy of the modified asphalt mixture also increased by 77.8%. Therefore, the low-temperature
cracking resistance of diatomite and basalt fiber composite modified asphalt mixtures was significantly
improved compared with the base asphalt mixture. With respect to the moisture stability, the residual
Marshall stability and freeze-thaw splitting ratio of the modified asphalt mixture were improved by
7.1% and 8.0%, respectively. This is because diatomite increases the cohesive force of asphalt mortar,
enhances the overall structural performance of asphalt mixture, and the special network structure of
basalt fibers also plays a role in anti-spalling and water damage.
Therefore, the low-temperature cracking resistance of diatomite and basalt fiber composite modified
asphalt mixtures was significantly improved compared with the base asphalt mixture. With respect
to the moisture stability, the residual Marshall stability and freeze-thaw splitting ratio of the modified
asphalt mixture were improved by 7.1% and 8.0%, respectively. This is because diatomite increases
the cohesive
Sustainability force
2019, of asphalt mortar, enhances the overall structural performance of asphalt mixture,
11, 5282 12 of 15
and the special network structure of basalt fibers also plays a role in anti-spalling and water damage.

6000 40
Control Group Experimental Group
35

(%) stability (cycle/mm)

5000

Cracking energy (Jm)

30
+66.7%
4000 +77.8% 25
Sustainability 2019, 11, x FOR PEER REVIEW 13 of 16
3000 20
100 Control Group Experimental Group 100
15
2000 +7.1%
Dynamic

+8.0%

Tensile strength ratio (%)Tensile strength ratio (%)

80 8010
Marshall stability

1000
5
60 0 600
High-temperature rutting Low-temperature splitting
Sustainability 2019, 11, x FOR PEER REVIEW 13 of 16
40 (a) 40
100 Control Group Experimental Group 100
Residual Marshall stability Residual

20 +7.1% 20
(%)

+8.0%
80 80
0 0
Residual Marshall stability Freeze-thaw splitting ratio
60 60
(b)
Figure 4. The conventional pavement performances of asphalt mixtures: (a) high and low temperature
40 40
test; (b) moisture stability test.

With regard to sound20 and vibration absorption performances of asphalt20 mixtures, SAA and DR
were chosen to characterize the sustainable performances, and the comparison results are illustrated
in Figure 5. From Figure 5, the addition of diatomite and basalt fiber composite modifier could
0 0
significantly improve the sound absorption performance of the asphalt mixture by about 38.5%. At
Residual Marshall stability Freeze-thaw splitting ratio
the same time, the vibration reduction of the diatomite and basalt fiber composite modified asphalt
(b)
mixture also improved, and the DR improved by 10.9% compared with the base asphalt mixture,
whichFigure
means
Figure 4.
4. The
The conventional
the modified
conventional pavement
asphalt performances
pavement
pavement of asphalt
had a more
performances of mixtures:performance.
comfortable
asphalt mixtures: (a)
(a) high
high and
and low temperature
Moreover,
low crumb
temperature
test;
rubber was
test; (b) moisture
(b) proven stability
moisturetostability
improve test.
test.the acoustic performances of asphalt pavement [39,40].

0.15 and vibration absorption performances of asphalt0.06

With regard to sound mixtures, SAA and DR
Control Group Experimental Group
were chosen to characterize the sustainable performances, and the comparison results are illustrated
in Figure 5. From Figure 0.05
0.12 5, the addition of diatomite and basalt fiber composite
+10.9%
modifier could
significantly improve the sound absorption performance of the asphalt mixture by about 38.5%. At
+38.5%
0.04 modified asphalt
the same time, the vibration reduction of the diatomite and basalt fiber composite
0.09 and the DR improved by 10.9% compared with the base asphalt mixture,
mixture also improved,
SAA

DR

0.03 Moreover, crumb

which means the modified asphalt pavement had a more comfortable performance.
rubber was proven to0.06
improve the acoustic performances of asphalt pavement [39,40].
0.02
0.15 0.06
Control Group Experimental Group
0.03
0.01
0.05
0.12 +10.9%
0.00 +38.5% 0.00
SAA DR 0.04
0.09
SAA

Figure 5. The sound

5. The sound and
and vibration
vibration absorption
absorption performances
performances of
of asphalt
asphalt0.03
mixtures.
DR

Figure mixtures.
0.06
4. Conclusions 0.02
In this study, the Marshall design indices and sound and vibration absorption properties of
0.03
waste crumb rubber modified asphalt mixtures with diatomite and basalt 0.01
fibers were carried out
based on the orthogonal design experiment using different diatomite content, basalt fiber content,
0.00 0.00
Sustainability 2019, 11, 5282 13 of 15

With regard to sound and vibration absorption performances of asphalt mixtures, SAA and DR
were chosen to characterize the sustainable performances, and the comparison results are illustrated
in Figure 5. From Figure 5, the addition of diatomite and basalt fiber composite modifier could
significantly improve the sound absorption performance of the asphalt mixture by about 38.5%. At
the same time, the vibration reduction of the diatomite and basalt fiber composite modified asphalt
mixture also improved, and the DR improved by 10.9% compared with the base asphalt mixture, which
means the modified asphalt pavement had a more comfortable performance. Moreover, crumb rubber
was proven to improve the acoustic performances of asphalt pavement [39,40].

4. Conclusions
In this study, the Marshall design indices and sound and vibration absorption properties of
waste crumb rubber modified asphalt mixtures with diatomite and basalt fibers were carried out
based on the orthogonal design experiment using different diatomite content, basalt fiber content,
and asphalt-aggregate ratios. Then, the range and variance analyses were adopted to investigate
the orthogonal experimental design for the mix proportion. Finally, the conventional pavement
performances and sustainable sound and vibration absorption properties of the optimal modified
asphalt mixture were also analyzed and evaluated compared to the base asphalt mixture. Therefore,
the experimental findings were drawn as follows:

• Based on the range and variance analysis of orthogonal experiment, the influence order of three
orthogonal factors on VA, VMA, VFA, and MS was asphalt-aggregate ratio > diatomite content >
basalt fiber content, which indicates that asphalt-aggregate ratio had the most significant influence.
Besides, it was found that diatomite had the most significant influence on sound absorption, and
basalt fiber had the most significant influence on vibration reduction.
• Considering the specification requirements as well as better performances of modified asphalt
mixture, the optimal mix proportion in the orthogonal experiment was determined as follows:
diatomite content at 7.5%, basalt fiber content at 0.3%, and asphalt-aggregate ratio at 5.5%.
• Compared to the base asphalt mixture, the high-temperature rutting, low-temperature splitting,
moisture stability, as well as sound and vibration absorption properties of the waste crumb rubber
modified asphalt mixture with diatomite and basalt fiber were improved to different extents.
• Due to the microporous structure of diatomite, diatomite can enhance the adhesion of asphalt
mortar, and the spatial network structure formed by basalt fibers plays an important role. Thus,
to some extent, diatomite and basalt fibers could reinforce the asphalt mixture. Besides, the
addition of diatomite and basalt fiber would improve the sound and vibration absorption
properties significantly.
• A test road will be constructed with the optimal mix proportion and tested through sound and
vibration absorption experiments, which provides a guidance for composite modified asphalt
mixtures and a reference for the sound and vibration absorption performances.

Author Contributions: Conceptualization, W.W. and Y.C.; methodology, W.W., H.C., Z.L., and G.T.; validation,
Y.C. and H.C.; formal analysis, H.C., G.T., and Y.B.; Investigation, W.W., Z.L., and Y.B.; writing—original draft
preparation, W.W.; writing—review and editing, Y.C. and G.T.; project administration, Y.C. and W.W.; funding
acquisition, W.W.
Funding: This research was supported by the Graduate Innovation Fund of Jilin University, grant number
101832018C003, and the China Scholarship Council, grant number 201906170186, and was funded by the National
Natural Science Foundation of China, grant number 51678271, and the Science Technology Development Program
of Jilin Province, grant number 20160204008SF.
Acknowledgments: The authors would like to appreciate the anonymous reviewers for their constructive
suggestions and comments to improve the quality of the paper.
Conflicts of Interest: The authors declare no conflict of interest.
Sustainability 2019, 11, 5282 14 of 15

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