Vigorous and continued efforts by researchers and engineers have contributed towards maintaining environmental sustainability through the utilization of waste materials in civil engineering applications as an alternative to natural sources. In this study, granite aggregates in asphaltic mixes were replaced by electric arc furnace (EAF) steel slag aggregates with different proportions to identify the best combination in terms of superior performance. Asphalt mixtures showing the best performance were further reinforced with polyvinyl alcohol (PVA), acrylic, and polyester fibers at the dosages of 0.05%, 0.15%, and 0.3% by weight of the aggregates. The performance tests of this study were resilient modulus, moisture susceptibility, and indirect tensile fatigue cracking test. The findings of this study revealed that the asphalt mixtures containing coarse steel slag aggregate exhibited the best performance in comparison with the other substitutions. Moreover, the reinforced asphalt mixtures with synthetic fibers at the content of 0.05% exhibited an almost comparable performance to the unreinforced asphalt mixtures. Modifying the asphalt mixtures with PVA, acrylic, and polyester fibers at the proportion of 0.15% have improved the fatigue cracking resistance by 41.13%, 29.87%, and 18.97%, respectively. Also, the fiber-modified asphalt mixtures with PVA, acrylic, and polyester have enhanced the fatigue cracking resistance by about 57%, 44%, and 39%, respectively. The results of the resilient modulus demonstrated that as the fiber content increase, the resilient modulus of the reinforced asphalt mixtures decreases. Therefore, introducing synthetic fibers at the content of 0.3% has slightly decreased the resilient modulus in comparison with unreinforced mixtures. On the other hand, the results of the mechanistic-empirical pavement design showed that the reinforced asphalt mixes with a high content of synthetic fibers have shown lower service life than the control mixes due to the low resilient modulus. On the contrary, based on the laboratory results, the asphalt mixes incorporating PVA, acrylic, and polyester fibers at the proportion of 0.15% have shown the potential to reduce the thickness of the asphalt layer by about 14.9%, 11.80%, and 8.70%, respectively.
Management and getting rid of waste materials become a major issue in recent years due to the large quantities of waste and by-product materials generated from multiple industries. Therefore, researchers have made efforts to use industrials wastes as an alternative for natural aggregate in civil engineering applications as a strategy to ensure environmental sustainability. Steel slag aggregate is one of the common waste materials used in civil engineering applications because of its characteristic properties that improve the mechanical properties of the asphalt mixtures. The utilization of steel slag aggregates in asphalt mixtures has become the focus of researchers’ attention due to the superior performance of the asphalt mixtures incorporating steel slag aggregates. Several studies have assessed the asphalt mixtures incorporating steel slag aggregates. Behnood et al. [
Nevertheless, one of the main problems associated with utilizing steel slag aggregate in asphalt mixtures is its high density, which increases the cost of transportation. In this regard, enhancing the mechanical properties of the asphalt mixtures by modifying the asphalt mixtures with certain additives may allow the thickness of the asphalt layer to be decreased. Thus, transportation and construction costs are minimized. Modifying the binder with the additives of polymer and copolymers has been documented as a successful strategy regarding improving the properties of the binder, which in turn enhances the performance of the asphalt mixes. Otherwise, modifying the binder with polymer and copolymer additives produce asphalt mixtures susceptible to aging [
Carbon fiber is a type of synthetic fiber with its unique properties regarding its high melting point (over 1000°C), high tensile strength, and high thermal conductivity. The utilization of carbon fiber has been evaluated on asphalt mixtures for many years. Jahromi et al. [
Basalt fiber is another type of synthetic fiber made from fine basalt fiber. Basalt fiber is characterized by its high melting point (higher than 1000°C) and high tensile strength (4500 MPa). The utilization of basalt fiber in the asphalt mixture has been performed in many studies. Morova [
Glass fiber is a type of inorganic fiber with a high melting point and high tensile strength. Fiberglass has been used vastly to improve the properties of the asphalt mixture. Guo et al. [
Nylon fiber is a type of synthetic polymers. Various studies have shown that reinforcing the asphalt mixtures with nylon fiber heightens the efficiency of properties of the asphalt mixtures. Lee et al. [
Aramid fiber is another type of synthetic fiber, which is characterized by its high melting point over 500°C and its high tensile strength (3800 MPa). Klinsky et al. [
Furthermore, Alnadish et al. [
In this study, the suitability of using steel slag aggregates in asphalt mixtures was investigated. The natural aggregates were substituted with different proportions of steel slag aggregates
The dense-graded asphalt mixtures were prepared with a binder of 80/100 penetration grade, which is produced by PETRONAS (Kuala Lumpur, Malaysia). The physical properties of the binder are summarized in
Properties | Result | Standard |
---|---|---|
Bitumen grade | 80/100 | – |
Penetration @ 25°C (0.1 mm) | 93 | ASTM D5 [ |
Softening Point (°C) | 45 | ASTM D36 [ |
Ductility @ 25°C (cm) | 141 | ASTM D113 [ |
Penetration Index (PI) | −1 | – |
Viscosity @ 135°C (mPa.s) | 487 | – |
Viscosity @ 165°C (mPa.s) | 144 | ASTM D4402 [ |
Mixing temperature | 160°C | ASTM D2493 [ |
Compaction temperature | 150 °C | ASTM D2493 [ |
Properties | Result | Specification | Standard | |
---|---|---|---|---|
Granite | Steel slag | |||
Loss angeles abrasion | 22 | 17.80 | ≤25% | ASTM C131 [ |
Aggregate crushing value (%) | 25 | 22.60 | ≤25% | IS: 2386 (Part IV) [ |
Bulk S.G. (g/cm3) | 2.63 | 3.22 | N/A | ASTM C127 [ |
Water absorption (%) | 0.84 | 2.75 | ≤3% | ASTM C127 |
Flat and elongated (%) | 8.40 | 3.90 | ≤10% | ASTM D4791 [ |
Angularity (%) | 84 | 95 | ≥80% | ASTM D5821 [ |
Free CaO content (%) | – | 1.17 | ≤4% | – |
Physical properties | Polyvinyl alcohol (PVA) | Acrylic | Polyester |
---|---|---|---|
Density (g/ cm3) | 1.29 | 1.17 | 1.38 |
Tensile strength (MPa) | >1200 | >700 | >500 |
Young’s modulus (GPa) | >20 | >28 | >7 |
Melting Point (°C) | >200 | >230 | >240 |
Color | Light yellow | Yellow | White |
Length (mm) | 6 | 6 | 6 |
Diameter (μm) | 10–20 | 10–25 | 10–25 |
In this study, granite aggregates were substituted by steel slag aggregate
To study the positive effect of the steel slag aggregates and synthetic fibers on the performance of the asphalt mixtures different tests were carried out.
The resilient modulus of the asphalt mixtures is an important variable in the mechanistic-empirical pavement design for the pavement structures. The resilient modulus test was conducted by means of a Universal Testing Machine (UTM-5P) (Inopave Group, Singapore). This test was conducted in accordance with ASTM D7369 [
The moisture susceptibility test was performed to study the resistance of the asphalt mixtures to moisture damage. This test was carried out following the procedures stated in AASHTO T 283 [
The resistance of the asphalt mixtures to cracking was investigated through the test of repeated indirect tensile strength by means of Universal Testing Machine (UTM-5P) (Inopave Group, Singapore). Three specimens were tested per mix. This test was conducted in accordance with the specifications in BS EN 12697-24 Annex E [
This section presents the results of the performance tests of the unreinforced asphalt mixtures.
The results of the resilient modulus are utilized as indication for the performance of the asphalt mixtures. The higher resilient modulus at 25°C implies the better resistance to cracking. Also, the higher resilient modulus at 40°C, the lower the permanent deformation.
The resistance of the unreinforced asphalt mixtures to moisture sensitivity is shown in
This section focuses on the results of the asphalt mixtures containing coarse steel slag aggregates and reinforced with polyvinyl alcohol (PVA), acrylic, and polyester fibers.
The T-test was conducted by means of Origin 9 software to compare the difference in the resilient modulus at the temperatures of 25 and 40°C. The test was selected to study the difference between the groups with the assumption that the normality of the data was attained. The assumption of normality was assessed by means of the Anderson–Darling test. As seen in
Group | Statistic | p-value | Decision at level (5%) |
---|---|---|---|
1 | 0.46338 | 0.23873 | Can’t reject normality |
2 | 0.34758 | 0.45544 | Can’t reject normality |
Group | N | Mean | SD | SEM | |
---|---|---|---|---|---|
1 | 30 | 6343.13 | 298.782 | 54.54998 | |
2 | 30 | 793.233 | 18.9512 | 3.46001 | |
T-test statistics | |||||
t Statistic | DF | p-value | |||
Equal variance assumed |
101.5357 | 58 | 0.000 | ||
Equal variance not assumed (Welch correction) | 101.5357 | 29.2333 | 0.000 |
The indirect tensile strength of the unconditioned samples is used as an indication of the resistance of the asphalt mixes to cracking. The high indirect tensile strength indicates that the mixtures are less susceptible to cracking.
Moisture susceptibility of the asphalt mixtures is considered as one of the main distress that influences the performance of the asphalt layer [
The test of Anderson–Darling was carried out to study the distribution of the data for the effect of moisture on the indirect tensile strength (ITS) of the asphalt mixtures.
Group | Statistic | p-value | Decision at level (5%) |
---|---|---|---|
1 | 0.72912 | 0.05115 | Can’t reject normality |
2 | 0.76147 | 0.04235 | Reject normality |
Group | N | Mean rank | Sum rank |
---|---|---|---|
1 | 30 | 21.55 | 646.5 |
2 | 30 | 39.45 | 1183.5 |
Mann-Whitney test statistics | |||
U | Z | p-value | |
181.5 | 3.962 | 0.000 |
PVA fiber | ||||||
---|---|---|---|---|---|---|
Group | N | Mean rank | Sum rank | |||
1 | 3 | 3 | 9 | |||
2 | 3 | 4 | 12 | |||
3 | 3 | 8 | 24 | |||
4 | 3 | 11 | 33 | |||
Kruskal-Wallis test statistics | ||||||
Chi-square | DF | p-value | ||||
9.461 | 3 | 0.02374 | ||||
Acrylic fiber | ||||||
Group | N | Mean rank | Sum rank | |||
1 | 3 | 3 | 9 | |||
2 | 3 | 4 | 12 | |||
3 | 3 | 8 | 24 | |||
4 | 3 | 11 | 33 | |||
Kruskal-Wallis test statistics | ||||||
Chi-square | DF | p-value | ||||
9.467 | 3 | 0.0233 | ||||
Polyester fiber | ||||||
Group | N | Mean rank | Sum rank | |||
1 | 3 | 4 | 12 | |||
2 | 3 | 3 | 9 | |||
3 | 3 | 8.66667 | 26 | |||
4 | 3 | 10.33333 | 31 | |||
Kruskal-Wallis test statistics | ||||||
Chi-square | DF | p-value | ||||
8.74359 | 3 | 0.0329 |
PVA fiber | |||||
---|---|---|---|---|---|
Group | N | Mean rank | Sum rank | ||
1 | 3 | 2.67 | 8 | ||
2 | 3 | 4.33 | 13 | ||
3 | 3 | 8 | 24 | ||
4 | 3 | 11 | 33 | ||
Kruskal-Wallis test statistics | |||||
Chi-square | DF | p-value | |||
9.667 | 3 | 0.02162 | |||
Acrylic fiber | |||||
Group | N | Mean rank | Sum rank | ||
1 | 3 | 3.333 | 10 | ||
2 | 3 | 3.667 | 11 | ||
3 | 3 | 8 | 24 | ||
4 | 3 | 11 | 33 | ||
Kruskal-Wallis test statistics | |||||
Chi-square | DF | p-value | |||
9.36 | 3 | 0.02488 | |||
Polyester fiber | |||||
Group | N | Mean rank | Sum rank | ||
1 | 3 | 3.333 | 10 | ||
2 | 3 | 3.667 | 11 | ||
3 | 3 | 8 | 24 | ||
4 | 3 | 11 | 33 | ||
Kruskal-Wallis test statistics | |||||
Chi-square | DF | p-value | |||
9.3589 | 3 | 0.0249 |
The decrease in the thickness of the asphalt layer contributes towards saving the cost of the construction and the transportation of the materials as well as the environmental sustainability. In this study, the mechanistic-empirical pavement design (MEPD) by means of Bisar software was employed to investigate the possibility of decreasing the thickness of the asphalt layer incorporating steel slag aggregate and synthetic fibers. The allowable number of repetitions loads to fatigue and rutting failures are calculated by
where Nd is the allowable number of repetitions loads to produce a rut depth of 12.7 mm with. While
The allowable number of repetitions axles to fatigue failure is calculated as follow:
where Nf is the allowable number of repetitions loads until fatigue failure, while
where TBR is the service life of asphalt layer and
where LTR is the decrease in thickness of the asphalt layer, while Tu and Tm are the thickness of the unreinforced and reinforced asphalt layer.
Layer | Thickness (mm) | Resilient modulus (MPa) | Poisson’s ratio (ν) |
---|---|---|---|
HMA | 100 | Various | 0.35 |
Base | 250 | 350 | 0.4 |
Sub-base | 300 | 200 | 0.4 |
Subgrade | – | 100 | 0.45 |
The outputs of Bisar software are presented in
On the contrary, the results of the cracking tests showed that the reinforced asphalt mixtures with synthetic fibers at the content of 0.3% by weight of aggregates exhibited the highest resistance to cracking in comparison with the other proportions. Therefore, adopting the mechanistic-empirical pavement design approach in determining the possibility of decreasing the thickness and the extension in the service life of the asphalt layer may introduce inaccurate analysis due to the high elastic behavior of the reinforced asphalt mixtures. It is acknowledged that the high elastic behavior of the asphalt mixtures has a low resilient modulus. Accordingly, espousing the resilient modulus in assessing the possibility of reducing the thickness of the asphalt layer may present an inexact assessment, in particular for the reinforced asphalt mixture characterized by its high elastic behavior.
Mix type | LTR | h (mm) | εh | εv | Nf | Nd | TBR |
---|---|---|---|---|---|---|---|
Granite | 0 | 100 | 102.36 | 196.56 | 28592501 | 53595604 | – |
Steel slag | 0 | 100 | 97.91 | 194.19 | 34650894 | 56578889 | 1.21 |
The reinforced asphalt mixtures with synthetic fibers at the proportion of 0.05% | |||||||
0 | 100 | 93.51 | 191.86 | 42263812 | 59727512 | 1.22 | |
PVA | 5 | 95 | 97.83 | 197.25 | 34778379 | 52759321 | 1.00 |
10 | 90 | 102.14 | 202.64 | 28860630 | 46760229 | 0.83 | |
0 | 100 | 95.21 | 192.77 | 39099526 | 58486198 | 1.13 | |
Acrylic | 5 | 95 | 99.53 | 198.16 | 32284240 | 51692420 | 0.93 |
10 | 90 | 103.84 | 203.55 | 26874569 | 45839491 | 0.78 | |
0 | 100 | 95.7 | 193.03 | 38240548 | 58133631 | 1.10 | |
Polyester | 5 | 95 | 100.02 | 198.42 | 31605345 | 51389254 | 0.91 |
10 | 90 | 104.33 | 203.81 | 26332629 | 45577746 | 0.76 | |
The reinforced asphalt mixtures with synthetic fibers at the proportion of 0.15% | |||||||
0 | 100 | 95.63 | 192.99 | 38366327 | 58185699 | 1.11 | |
PVA | 5 | 95 | 99.95 | 198.38 | 31704805 | 51434030 | 0.91 |
10 | 90 | 104.26 | 203.77 | 26412061 | 45616408 | 0.76 | |
0 | 100 | 96.05 | 193.21 | 37649986 | 57887086 | 1.09 | |
Acrylic | 5 | 95 | 100.36 | 198.6 | 31138124 | 51177218 | 0.90 |
10 | 90 | 104.68 | 203.99 | 25959317 | 45394651 | 0.75 | |
0 | 100 | 97.26 | 193.85 | 35669520 | 57034192 | 1.03 | |
Polyester | 5 | 95 | 101.57 | 199.24 | 29568420 | 50443472 | 0.85 |
10 | 90 | 105.89 | 204.63 | 24703012 | 44760864 | 0.71 | |
The reinforced asphalt mixtures with synthetic fibers at the proportion of 0.3% | |||||||
0 | 100 | 98.329 | 194.42 | 34018830 | 56290328 | 0.98 | |
PVA | 5 | 95 | 102.64 | 199.81 | 28256612 | 49803228 | 0.82 |
10 | 90 | 106.96 | 205.20 | 23650547 | 44207597 | 0.68 | |
0 | 100 | 99.99 | 195.30 | 31640698 | 55160034 | 0.91 | |
Acrylic | 5 | 95 | 104.31 | 200.69 | 26360864 | 48829849 | 0.76 |
10 | 90 | 108.63 | 206.08 | 22125265 | 43366014 | 0.64 | |
0 | 100 | 101.18 | 195.93 | 30063246 | 54367939 | 0.87 | |
Polyester | 5 | 95 | 105.50 | 201.32 | 25099399 | 48147328 | 0.72 |
10 | 90 | 109.82 | 206.72 | 21107353 | 42775587 | 0.71 |
In this study, the possibility of reducing the thickness of the reinforced asphalt layer was evaluated using the results of the cracking tests (static and dynamic (repeated) indirect tensile strength). It is recognized that the results of the indirect tensile strength test are in a strong relationship with the results of the other cracking tests. The higher the indirect tensile strength, the higher the resistance to cracking. Therefore, the results of the indirect tensile strength and the repeated indirect tensile strength were chosen to investigate the possibility of decreasing the thickness of the reinforced asphalt layer because the outputs of Bisar software showed that the critical damage was fatigue cracking.
Modifying the asphalt mixtures with the synthetic fibers of PVA, acrylic, and polyester at the content of 0.15% by weight of the aggregates may increase the cost of the production by about 10.9%, 7.6%, and 5.4%, respectively. On the other hand, reinforcing the asphalt mixes with the synthetic fibers of PVA, acrylic, and polyester at the dosage of 0.3% by weight of the aggregates may raise the cost of production by about 22%, 15%, and 11% per ton, respectively. Therefore, the fiber-modified asphalt mixtures with the synthetic fibers at the content of 0.15% by weight of the aggregates are the best in economic terms.
Mix type | Type of fiber | ITS (MPa) | Cycles to failure | ITS improvement rate (%) | Cycles improvement rate (%) |
---|---|---|---|---|---|
Mix0 | – | 0.966 | 9250 | – | – |
PVA | 0.975 | 9791 | 0.94 | 5.85 | |
Mix1 | Acrylic | 0.972 | 9440 | 0.62 | 2.05 |
Polyester | 0.969 | 9389 | 0.30 | 1.50 | |
PVA | 1.11 | 13055 | 14.90 | 41.13 | |
Mix2 | Acrylic | 1.08 | 12013 | 11.80 | 29.87 |
Polyester | 1.05 | 11005 | 8.70 | 18.97 | |
PVA | 1.21 | 14581 | 25.26 | 57.63 | |
Mix3 | Acrylic | 1.14 | 13389 | 18.01 | 44.74 |
Polyester | 1.11 | 12873 | 14.90 | 39.17 |
Based on the results of this study, the following conclusions were made:
The asphalt mixes incorporated coarse steel slag aggregate exhibited the best performance in comparison with the other substitutions in terms of the resilient modulus and fatigue resistance. While the asphalt mixes incorporating 100% of steel slag aggregates exhibited the worst performance. Reinforcing the asphalt mixtures with synthetic fiber at the content of 0.05% have shown an almost comparable performance to the unreinforced asphalt mixes. Moreover, introducing synthetic fiber at the dosages of 0.15% and 0.3% exhibited the best resistance to cracking as compared to the other mixtures. The outputs of mechanistic-empirical pavement design demonstrated that the resilient modulus of the asphalt mixtures has a direct influence on the allowable repetitions loads to fatigue and rutting damage. The higher the resilient modulus, the higher the allowable repetitions loads. Thus, reinforcing the asphalt mixtures with synthetic fibers at the content of 0.3% showed lower repetitions loads as compared to the other mixtures. This is attributed to the high elastic behavior of the reinforced asphalt mixtures. The results of cracking tests showed that the resistance of the asphalt mixes to cracking increases with the increase of fiber content. Therefore, assessing the possibility of decreasing the thickness and extending the lifespan of the asphalt layer based on the laboratory tests may produce a better evaluation and understanding than the mechanistic-empirical pavement design, in particular for the asphalt mixture characterized by its high elastic behavior. The fiber-modified asphalt mixtures with the synthetic fibers of PVA, acrylic, and polyester at the proportion of 0.15% possess the possibility to decrease the thickness of asphalt layer by about 14.9%, 11.80%, and 8.70%, respectively. Therefore, adding the synthetic fibers at the content of 0.15% by weight of the aggregates is the best in economic terms.
The authors would like to acknowledge Universiti Tun Hussein Onn Malaysia and Universiti Tenaga Nasional for technical and financial support to this research.