The objective of this research was to investigate rutting and fatigue distresses in asphalt containing 2, 4, 6, and 8 percent of nanosilica (NC) and to find out the correlation between engineering properties of the modified binder and mixture asphalt. In order to study the effect of NC on the rutting and fatigue properties of modified binders, the multiple stress creep recovery (MSCR) and linear amplitude sweep (LAS) tests were carried out. The Marshall stability, dynamic creep, and four-point bending beam fatigue tests were used to evaluate performance characteristics of the mixtures. The binder and mixture tests all indicated an improvement of fatigue and rutting resistance using NC as a modifier. Furthermore, some statistical correlations between engineering properties were developed successfully.
Binder plays an important role in preventing common distresses associated with asphalt mixture such as fatigue cracking and rutting. For instance, binder with enough adhesion and cohesion can significantly hinder the segregation and separation of aggregates from the pavement surface [
The effect of nanoclay as an asphalt binder additive on the mechanical properties of the asphalt mixture demonstrated a considerable increase on rutting resistance and resilient modulus of asphalt concrete (AC) samples. However, the additive has no considerable effect on low-temperature fatigue resistance of the modified sample [
Amirkhanian et al. studied the effects of carbon nanoparticles on the performance characteristics of asphalt binder. The viscosity, performance grade (PG), creep and creep recovery, and frequency sweep tests were carried out on modified binder. Experiment results indicate that the addition of the carbon nanoparticle was effective in increasing viscosity, failure temperature, complex modulus and elastic modulus, and as a result, rutting resistance of the binder [
Yao et al. used NC as a binder modifier. They added NC to an SBS-modified asphalt in 4 and 6 percent by the weight of the modified base binder. Experiment results showed that the value of viscosity at high temperatures decreased slightly; in fact, at low temperatures, modified binder with NC behaves similar to control binder samples; furthermore, NC improved binder antioxidation characteristics. The rutting and fatigue cracking performance of asphalt binder modified by NC was improved [
Among the advantages of NC are its functional features and low-cost production. NC is one of the new minerals which include potential useful features, such as huge surface area, good distribution, high absorption, high stability, and high percentage of purity.
Today, researchers are looking for binder tests that not only could demonstrate the mixture’s performance-related characteristics of both modified and unmodified binder but also are easy and quick to conduct. Insufficiency of the performance grade (PG) binder specification as one of the common methods to evaluate binder performance, especially when it is modified or rejuvenated by additives, has been proved by many researchers [
In this research study, the binder is modified by 2, 4, 6, and 8 percent of NC, and two important distresses of asphalt, rutting and fatigue, are evaluated through the LAS, MSCR, 4-point bending beam, and dynamic creep tests. Finally, some correlation between binder and mixture test results was developed successfully.
The asphalt binder used in this study was AC-60/70, provided by Pasargad Oil Company, Tehran. The characteristics of the binder are presented in Table
Physical properties measured of bitumen.
Parameter measured | Test method | Test value |
---|---|---|
Specific gravity at 25°C (g/cm3) | AASHTO T228 | 1.01 |
Penetration at 25°C (0.1 mm) | AASHTO T49 | 60 |
Softening point (R&B) (°C) | AASHTO T53 | 56 |
Viscosity at 120°C (centistokes) | AASHTO T201 | 1055 |
Viscosity at 135°C (centistokes) | AASHTO T201 | 361 |
Viscosity at 160°C (centistokes) | AASHTO T201 | 170 |
Ductility at 25°C (cm) | AASHTO T51 | >100 |
Properties of used aggregates.
Properties | Method | Requirement | Values |
---|---|---|---|
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Los Angeles abrasion (%) | AASHTO T96 | 30 max. | 20 |
Water absorption (%) | AASHTO T85 | 5 max. | 0.8 |
Bulk specific density (g/cm3) | AASHTO T85 | — | 2.654 |
Flat and elongated (3–1) (%) | ASTM D4791 | 20 max. | 12 |
Soundness (sodium sulfate) (%) | AASHTO T104 | 15 max. | 4.8 |
Crushed content (one face) (%) | ASTM D5821 | 100 min. | 100 |
Crushed content (two faces) | ASTM D5821 | 90 min. | 100 |
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Water absorption (%) | AASHTO T84 | — | 1.4 |
Bulk specific density (g/cm3) | AASHTO T84 | — | 2.617 |
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Bulk specific density (g/cm3) | AASHTO T84 | — | 2.702 |
Gradation of the aggregates used in the study.
Sieve sizes | US | 3/4″ | 1/2″ | No. 4 | No. 8 | No. 50 | No. 200 |
---|---|---|---|---|---|---|---|
Sieve sizes | Metric | 19 | 12.50 | 4.75 | 2.36 | 0.3 | 0.075 |
Passing (%) | HMA gradation | 100 | 95 | 60 | 40 | 15 | 5 |
Gradation of designated aggregates.
NC is added to the asphalt binder by 2, 4, 6, and 8 percent of the original binder’s weight. A high-shear mixing device is used to mix NC and binder with 4000 rpm for 2 hours at 135°C. The SEM images of the modified binder with 4 percent NC in three magnitudes are shown in Figure
SEM images of NC with asphalt binder: (a) 20
The Marshall method was used to determine the stability, flow, and optimum binder of all asphalt samples (ASTM D2726 and ASTM D1559). Percentage of optimum binders obtained were 5.5, 5.3, 5.2, 5 and 4.9 at mixtures with 0%, 2%, 4%, 6% and 8% of NC content, respectively. The samples were compacted using a Gyratory compactor for the dynamic creep, indirect tensile strength, and resilient modulus tests. Samples used in fatigue tests were originally fabricated as slabs with dimensions of 5
The binder performance characteristic tests have been carried out on aged samples. Prior to the multiple stress creep recovery (MSCR) and linear amplitude sweep (LAS) tests, all the modified binder samples, as well as the 60/70 base binder, were aged in the rolling thin-film oven (RTFO) in order to represent a short-term aging condition.
This test has been used to measure the percent of recovered strain (
This test was proposed by Johnson and Hintz to investigate the fatigue resistance of asphalt binders [
In the viscoelastic continuum damage (VECD) analysis, the binder fatigue performance parameter
The test was carried out according to ASTM D1559. Before the test, all samples were put in 60°C water for 30 minutes. Marshall stability is the peak resistance load obtained during a constant rate of the deformation load sequence, and Marshall flow is a measure of deformation of the asphalt mix determined during the stability test. The Marshall quotient equals the ratio of the Marshall stability to the value of the Marshall flow. The value of the Marshall quotient indicates the resistance of asphalt mixtures against permanent deformations and the value of rutting [
Resilient modulus is one of the important parameters in the pavement design procedure. The measurement of this parameter is in the form of pavement response under dynamic loads and the corresponding strains associated with them. The value of resilient modulus is measured based on the ASTM D4123 [
In the present research, the dynamic creeping test has been used to evaluate the rutting property of the asphalt mixtures. The output creep curve of the test is made of three areas. In the present article, the flow number (
The fatigue life of the asphalt mixtures is evaluated by the 4-point bending beam test under AASHTO-T321 standard specifications. A constant sinusoidal loading was applied on beam specimens at constant strain levels of 600, 800, and 1000 microstrains until 50 percent reduction of initial stiffness.
The MSCR test encompasses different outputs. The accumulated strain versus time over a 10-cycle period for the shear stress values of 100 Pa and 3200 Pa is shown in Figure
Summary of MSCR test results.
The values of percent recovered strain (
The permanent deformation characteristics of binders can be quantified by the
The results of linear amplitude sweep (LAS) tests are analyzed based on the theory of viscoelastic continuum damage. Utilizing this theory,
Linear amplitude sweep (LAS) test results.
Parameters | 0% NC | 2% NC | 4% NC | 6% NC | 8% NC |
---|---|---|---|---|---|
|
33,200 | 49,334 | 57,990 | 134,765 | 146,928 |
|
−1.92 | −2.09 | −2.13 | −2.35 | −2.45 |
The increase in the absolute value of
The trend of fatigue life of asphalt binders based on the VECD theory is depicted in Figure
Fatigue models from the VECD analysis.
Table
Summary of mixture test outcomes.
Control | Mixture + 2% NC | Mixture + 4% NC | Mixture + 6% NC | Mixture + 8% NC | ||
---|---|---|---|---|---|---|
Average Marshall stability (KN) | — | 10.23 | 11.30 | 12.10 | 12.73 | 13.40 |
Average Marshall flow (mm) | — | 4.2 | 4.32 | 4.41 | 4.55 | 4.72 |
MQ (KN/mm) | — | 2.44 | 2.62 | 2.74 | 2.80 | 2.84 |
|
@600 |
106,092 | 120,477 | 141,428 | 151,623 | 158,685 |
@800 |
76,738 | 85,541 | 113,843 | 139,781 | 147,428 | |
@1000 |
26,246 | 33,888 | 38,133 | 42,355 | 43,414 | |
Resilient modulus | @25°C | 3520.2 | 3707.5 | 3976.2 | 4420.6 | 4828.5 |
@5°C | 11,884.6 | 12,826.2 | 13,255.3 | 13,988.7 | 14,711.5 |
Resilient modulus (
Dynamic creep test results indicate that asphalt mixtures modified with NC have higher resistance against permanent deformation in comparison to control samples. Such an increase in NC can raise the flow number, which is a parameter of resistance against rutting. Increasing the amount of NC by 8% led to an almost 71% increase in the flow number. This finding is in a good agreement with other researchers [
In the 4-point bending beam test, it was observed that, by increasing the percentage of NC, the variation trend of
Further details and discussions about engineering performance of NC-modified mixture are presented in another article by the same authors [
A series of linear regression models between binder test results, which are considered as independent, and mixture test results, which are considered as dependent, are developed. Linear regression is a statistical method that defines the relationship between two independent variables [
Summary of correlation equations and regression coefficients.
Dependent variable ( |
Independent variable ( |
Equation |
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0.8097 |
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0.9086 |
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0.8712 |
Dynamic creep |
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|
0.9626 |
Dynamic creep |
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0.9829 |
Marshall |
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0.9915 |
Marshall |
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0.9976 |
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0.9816 |
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0.9755 |
Correlation between independent vriables (a) A35 vs. Jnr100 and (b) Jnr100 vs. R3200.
Results of the flow number of mixture versus nonrecoverable compliance (
Flow number of mixture versus (a)
Fatigue properties of the mixture are strongly correlated to those of binders. Therefore, modifying the binder could considerably alter fatigue behavior of the mixture, and the binder test could give us a good estimation of fatigue characteristics of the mixture [
Fatigue life of mixture (
The Marshall stiffness index (or Marshall quotient) represents the resistance of the material to shear stress and permanent deformation. Higher MQ means the mixture is stiffer and is more resistant against rutting. The permanent deformation characteristics of binders are quantified by the
Marshall quotient versus (a)
Resilient modulus is an indicator of a material’s deflection behavior. In this research, resilient modulus at both 5°C and 25°C is correlated with
Resilient modulus at 5°C and 25°C versus
The results of the MSCR test indicate improvement of elastic properties of modified asphalt binders at a high temperature. They also show that NC not only increases rutting resistance in modified asphalt but also reduces its stress sensitivity. Results of the MSCR test are in line with the results obtained from the dynamic creep test, presenting a strong correlation between performance of the binder and mixture. Overall, it can be deduced that the binder modified by NC contributes to resistance of the asphalt mixture against permanent deformations. The LAS test results indicate a considerable increase in the fatigue life of the NC-modified asphalt binder at low strain levels. On the other hand, the fatigue life of modified asphalt binders at high strain levels is a little less than that of the unmodified binders. Furthermore, the results of the four-point bending beam test demonstrate that adding NC up to 8 percent by binder content could considerably improve fatigue resistance, which confirms the results of the LAS test. According to the correlation of the flow number, MQ, and According to a fairly well correlation between binder and mixture test outputs obtained in this research, it is promising to develop a phenomenological relation between characteristics of the binder and mixture using more extensive data and considering important parameters, in future research, so more time and materials are saved using binder tests instead of the mixture tests.
The authors declare that there are no conflicts of interest regarding the publication of this paper.