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Performance of asphalt mixture with nanoparticles
Performance of asphalt mixture with nanoparticles
8
Shaban Ali Zangena Civil Engineering Department, Faculty of Civil and Environmental Engineering, Near East University, Turkey
8.1
Introduction
The asphalt cement and asphalt mixtures need to be improved to reduce and prevent distresses. Polymers became a part of the materials used by humans in a lot of applications than any other categories of materials available, therefore to improve the properties of bitumen in the present world, polymers are used as additives to enhance asphalt cement and asphalt mixture properties because of their excellent physical and chemical properties. Polymers can be defined as large molecules composed of a large number of correlations of small particles with each other, and these small molecules are called monomers. Furthermore, there are six main thermoplastic polymers: polyvinyl chloride (PVC), polystyrene (PS), low-density polyethylene (LDPE), high-density polyethylene elements, and compounds in waste plastic such as copolymers, elastomers, and plastomers. Using an EVA polymer to investigate the mechanical behavior of the asphalt mixtures showed the highest resistance constant to deformation damage. The EVA polymer is one of the best solutions to improve the physical and mechanical properties of bitumen concrete as well as an excellent way to combat (principally rutting) permanent deformation damage (Saoula et al., 2009). Polymer modified asphalt (PMA) based on conventional tests and rheological properties with an increasing polymer content shows a significant increase in mechanical properties. On the other hand, rheological properties of PMBs represented higher complex modulus (G*) especially at high temperature and increased elastic properties of PMB at low frequency. Combination of polymers provides an opportunity to be reused and recycled and at the same time allows the possibility of maintaining sources as well as reduces the costs. On the other side, the combination of polymers successfully improved the performance and properties of asphalt (Peralta et al., 2010). The effectiveness of polymer concentration on the microstructure, thermal, and rheological properties using recycled polyethylene modified bitumen comes out with significant modification of the rheological reaction. Recycled polyethylene (RPE) polymer increases the principles of viscosity and storage as well as causes a decrease in thermal susceptibility. As a result, asphalt cement modification with RPE yields improved mechanical characteristics, thus higher resistance to rutting and also to fatigue and thermal cracking (Peralta et al., 2010). Once polymers are added to the asphalt, sometimes or in some cases, the
Nanotechnology in Eco-efficient Construction. https://doi.org/10.1016/B978-0-08-102641-0.00008-6 Copyright © 2019 Elsevier Ltd. All rights reserved.
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separation occurs between polymers and asphalt which results in poor adhesion between binder and aggregates with time, so nanotechnology appeared to be another solution to improve asphalt quality. Nanotechnology has recently become one of the attractive research fields in civil engineering and construction materials. Conventionally, it has led to advances in the areas of materials science, microelectronics, and medicine. However, several developments in nanotechnology may be applied to the field of construction engineering (Rana et al., 2009). The manufacture of new materials at the molecular level on the nanoscale leads to phenomena associated with atomic and molecular interactions to strongly affect the materials’ macroscopic properties (Chong, 2004). Nanoscale modification improves some characteristics of asphalt binders and asphalt mixtures, such as rutting and fatigue, but more investigations are required before it can be applied on a large scale (Khattak et al., 2012). As the nanotechnology is a creation of new materials and engineers are interested in studying the material properties at the level of macro and nanoscales, the nano and microscales afford fundamental insights into the development of science and technology. Fig. 8.1 shows the development of length scales of the asphalt material (You et al., 2011). Nanotechnology includes microscopic particles of a material; nanomaterials are new materials that recently become popular and one of the large and important parts in research and development worldwide, they are also defined as microscale fillers which would make polymers efficient as filler reinforcements (Mahshid et al., 2012). The obtained results from the modification of nanomaterials show improvement in mechanical behavior properties of asphalt mixtures, such as fatigue resistance, indirect tensile strength, and creep. Polymer based nanocomposites reinforced with montmorillonite nanoclay particles have drawn substantial interest; this is according to the fact that these types of composites show significant enhancements in thermal and mechanical properties compared to the virgin polymer. Also, many studies with the considerable nanocomposites show substantial improvements in strength and stiffness compared with those modified by polymer only, even by adding a small quantity of nanomaterial particles (Yasmin et al., 2006).
8.2 8.2.1
Types of nanoparticles modified asphalt mixture Nanoclay modified asphalt
The definition of nanoclay is clay that can be modified to make the clay complexes compatible with organic monomers and polymers. The common clays are occurring minerals and thus subjected to natural variation in their formation. The pureness of the clay plays a significant role in affecting the properties of the nanocomposite, and clay contains aluminaesilicates, which have a layered structure. It also includes silica SiO4 tetrahedron bonded to alumina AlO6 octahedron in several ways. Related to results of plastic limit is between the ranges of 85.4 up to 87.5%. The process of the nanoclay material is displayed in Fig. 8.2 (Jahromi and Khodaii, 2009).
Meso
Micro
Nano
Quantum
10–9
10–12
Aggregate Asphalt
100
10–3
10–6
Performance of asphalt mixture with nanoparticles
Macro
Figure 8.1 Development of length scales of asphalt. Source: You, Z., Mills-Beale, J., Foley, J.M., Roy, S., Odegard, G.M., Dai Q.,, Goh S.W., 2011. Nanoclay-modified asphalt materials: preparation and characterization. Construction and Building Materials 25 (2), 1072e1078.
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Figure 8.2 Nanoclay surface ttreatment. Source: Jahromi, S.G., Khodaii, A., 2009. Effects of nanoclay on rheological properties of bitumen binder. Construction and Building Materials 23 (8), 2894e2904.
Currently, several studies have been conducted to evaluate the effect of nanoclay particles on the performance of asphalt cement and several studies have been using the concentration of 2%e6%, and some researchers used up to 8% by weight of the asphalt cement. Jahromi and Khodaii (2009) evaluated the nanoclay effects on rheological properties of asphalt cement, the concentration of the modifier was 2, 4, and 7 wt%. The base asphalt cement was 60/70 penetration grade. Tests proved that the modifications of asphalt using nanoclay are able to increase the stiffness of the modified asphalt and delay the aging. It is observed that when asphalt was modified with a slight quantity of nanoclay, it successfully enhances the physical properties of asphalt. Moreover, the nanoclay materials have a higher aspect ratio and a huge surface area, and their particles are uniform in size and arrangement. Then, a small percentage of nanoclay modified asphalt cement able to change the rheological properties shows a decline of penetration, ductility, and an increase in softening point and aging resistance. DSR results also revealed that the sheer complex modulus (G*) increases with decreasing the temperature or increasing frequency, while the phase angle increases as the temperature increases or frequency decreases. Also, the temperature susceptibility of modified asphalt cement was reduced compared to the base asphalt cement, the results of the study show that the addition of the nanoclay had a good influence on the internal structure of the mixtures and, therefore, affects their
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rheological behavior (Jahromi and Khodaii, 2009). Zare-Shahabadi et al. used the organically modified bentonite (OBT) and bentonite clay (BT) to modified asphalt cement (60/70 penetration grade) with the addition of 1, 2, 4, 5, and 6 wt%, to investigate the physical properties and high temperature, dynamic rheological performance of the BT and OBT modified asphalt cement. Further, to evaluate the properties of low-temperature cracking of the modified asphalt cement after artificial short and long-term aging, they found that the OBT and BT modified asphalts have shown an increase in softening point and viscosity better than the base asphalt cement. Nonetheless, the ductility of the modified asphalt cement decreased with the addition of OBT and BT. Evaluation of dynamic rheological properties shows that the modified asphalt cement was better than the base asphalt cement and shows an increase in complex modulus and decrease in the phase angle which indicates that the rutting resistance of the modified asphalts was enhanced. Also, it is observed in the bending beam rheometer (BBR) test that creep stiffness was reduced. As a result, the resistance of low-temperature cracking was improved (Zare-Shahabadi et al., 2010). El-Shafie et al. (2012) investigated influences of macro and organically modified nanoclay on the properties of asphalt cement using local asphalt cement of penetration grade 60/70, a high-shear mixer was used to produce the asphalt nanocomposite at 160 C. Nanoclay was added to asphalt cement with concentrations of 2, 4, 6, and 8 wt%. The results revealed that the physical and mechanical properties of modified asphalt are significantly enhanced as the penetration decreases up to 25%, meanwhile the softening point increases up to 12 C compared to the base asphalt. The best asphalt performance was observed when the addition of nanoclay was 6% (El-Shafie et al., 2012). Abdullah et al. (2012) studied the physical properties and evaluated storage stability of the local asphalt modified with nanoclay and warm asphalt additives (WAA). The outcomes of the research showed that the modified asphalts had good storage stability; also they can improve the physical properties of asphalt, as the softening point increased and the penetration decreased. Moreover, a better decline of mixing and compaction of asphalt mixtures was observed (Abdullah et al., 2012). Yao et al. (2013) worked to investigate the rutting and fatigue resistance performance as well as changes in the microstructure of modified asphalt binders using the DSR and FTIR tests. The base asphalt cement was PG 58-34 modified with the acrylonitrile butadiene styrene (ABS). The materials used in this investigation were (A) nanometer nanoclay (NI.44P), (B) carbon microfibers (MCF), (C) nonmodified nanoclay (NMN), and (D) polymer modified nanoclay (PMN) as shown in Fig. 8.3. The concentrations of 2 and 4 wt% were added to the base asphalt. It was found that from the preparation and mixing of nano and micromodified asphalt, it is realized that the nano or micromaterials might have physical dispersion and chemical reactions with the base asphalt. Based on the DSR outcomes, the addition of all modifiers was able to increase the complex shear modulus compared to the base asphalt cement, and also improved the resistance to rutting. Results of FTIR spectroscopy show the addition
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Figure 8.3 SEM images of (A) nanometer nanoclay, (B) carbon microfibers, (C) nonmodified nanoclay, and (D) polymer modified nanoclay. Source: Yao, H., You, Z., Li, L., Goh, S.W., Lee, C.H., Yap, Y.K., Shi, X., 2013. Rheological properties and chemical analysis of nanoclay and carbon microfiber modified asphalt with Fourier transform infrared spectroscopy. Construction and Building Materials 38, 327e337.
of ultrafine materials in the asphalt cement, the oxidation response may be declining in the modified asphalt cement once it is exposed to heat and sunlight. Concisely, the consequence of modified asphalt on antioxidation enhanced when some ultrafine materials were added to the base asphalt (Yao et al., 2013). Santagata et al. (2015) evaluated the effects of sonication on high-temperature properties of base asphalt binder which is classified as a PG58-22 modified with nanoclay (NCA and NCB) and carbon nanotubes (CNT) investigated. Evaluation of the impacts of additives shows that the best resistance to rutting was found with using CNT and NCA, but the NCB displays a much lower capability to affect the rheological properties of base asphalt cement (Santagata et al., 2015). Ja and Hromi (2013) investigated the impact of nanoclay modified asphalt mixtures with concentrations of 0.2%, 0.4%, and 0.7% by weight of asphalt cement (60/70 penetration grade). Performed tests on dense asphalt mixtures indicate that the modifications using Cloisite-15A and Nanofill-15 increase the stiffness of modified asphalt mixtures and lead to improvements in the rutting resistance, resilient modulus, Marshall Stability, and indirect tensile strength. It is also noted that fatigue performance enhanced at low temperatures (Ja and Hromi, 2013).
Performance of asphalt mixture with nanoparticles
8.2.2
171
Nanosilica modified asphalt cement
One of the most abundant compound materials on earth is silica, it is mostly employed in manufacturing to produce colloidal silica, silica gels, and fumed silica. Worldwide, silica nanoparticles have been used in several industries such as medicine and engineering. Currently, silica nanocomposites become one of the conventional materials in the modification of asphalt cement and asphalt mixtures, it might be because of the low cost of manufacture and the high-performance structures of these nanomaterials (Lazzara and Milioto, 2010). Nanosilica particles have been used in many applications of civil engineering, starting from application of cement and cement composites to application of polymers and modification of asphalt cement. Fig. 8.4 shows a SEM image of nanosilica. Application of nanosilica modified asphalt cement shows better performance of asphalt cement and asphalt mixtures. Yao et al. (2013) investigated the rheological properties and chemical bonding of nanosilica modified base asphalt cement (PG 58-34). The asphalt was modified with acrylonitrile butadiene styrene (ABS) with a concentration of 4 and 6 wt% and depending on the results, they found that with an additional increase in the concentration of nanosilica in the base asphalt cement, the viscosity decreased slightly for modified asphalt cement. The complex modulus of modified asphalt cement decreases slightly compared to the base asphalt. Also, modified asphalt cement has good resistance to high-temperature rutting compared to the base asphalt cement or aging process samples. The Scanning Electron Microscopy (SEM) images observe that there are some changes in the microstructure of modified asphalt cement compared to the base asphalt cement. Also, they show that nanosilica particles have a good dispersion in the asphalt cement. Finally, the dynamic modulus of the modified asphalt mixture increases significantly compared to the unmodified asphalt mixture and the concentration of 6% has higher dynamic modulus than 4% at elevated temperatures. These indicate
Figure 8.4 SEM image of nanosilica at 3,000 magnification. Source: Kreyling et al., 2010.
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that the nanosilica modified asphalt mixture was able to enhance the rutting resistance (Yao et al., 2013).
8.2.3
Carbon nanotubes modified asphalt cement
Carbon nanotubes as shown in Fig. 8.5 are produced from pieces of graphite that have rolled up to form a tubular structure, various techniques were used to produce carbon nanotubes, the common two methods are using electricity and an inert gas in an enclosed chamber (Amirkhanian et al., 2011). As there is a need to improve the properties of asphalt cement, several studies have been conducted in application nanotechnology using carbon nanotubes. Amirkhanian et al. (2011) presented a study on the description of unaged asphalt cement modified with percentages of 0.2%, 0.5%, 1.0%, and 1.5% by weight of asphalt cement of carbon nanoparticles using PG 64-22 from three sources. The results show that the addition of nanoparticles increased the viscosity values of asphalt cement. However, at a low concentration of nanoparticles (0.2%) the increase is not significant, which might be because the modified blends are similar to the base asphalt. Meanwhile, the higher viscosity values were observed obviously with a concentration of 1.0% and 1.5% nanoparticles modified asphalt cement. Moreover, the addition of the modifier improves the resistance of rutting at high service temperatures, and a higher failure temperature was noted in modified asphalt cement with a high concentration of the modifier. Santagata et al. (2012) used the carbon nanotubes in asphalt application, using base asphalt cement 50/70 penetration grade and carbon nanotubes as a modifier; some carbon nanotubes modified asphalt cement blends were prepared at different
Figure 8.5 SEM images of carbon nanoparticles. Source: Amirkhanian, A.N., Xiao F., Amirkhanian, S.N., 2011. Characterization of unaged asphalt binder modified with carbon nanoparticles. International Journal of Pavement Research and Technology 4(5), 281e286.
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concentrations (0.1, 0.5, and 1.0 wt%). The rheological characterization was evaluated in different aging conditions: unaged, short-term aging using RTFOT, and long-term aging with PAV. From viscosity test results, an increase in viscosity with the addition of carbon nanotubes concentration can be observed. Specifically, viscosity improvements were of the order of 9% for the 0.1% carbon nanotubes and 25% for the order of 0.5% carbon nanotubes as well as up to 80% with 1% of carbon nanotubes, which has higher improvement among the blends. Besides, the analysis of results of frequency sweep test carried out on the mixtures shows that adding a high amount of carbon nanotubes results in a significant enhancement in stiffness and elasticity at high temperatures and low frequencies, thus they have beneficial impacts on the potential rutting resistance (Santagata et al., 2012). Motlagh et al. (2012) investigated the physical properties of asphalt cement using carbon nanotubes as a modifier of the base asphalt cement (60/70 penetration grade). The results show that the penetration decreased and softening point increased with the addition of modifiers. With increase in the carbon nanotube concentration it is found that the ductility increases much more than the base asphalt, which means the modified asphalt cement is more adhesive than unmodified asphalt (Motlagh et al., 2012).
8.3
Laboratory techniques for preparation of nanoparticles modified asphalt mixtures
There are three conventional materials used in the preparation of modified asphalt mixtures in the laboratory namely, asphalt cement, aggregates, and the modifier (nanomaterials), also there are different types of base asphalt cement which play a significant role in the properties of modified asphalt mixtures. The methods that are used to modify asphalt cement are usually two ways dry method which are used in the modification of asphalt mixtures by adding additives as fillers, while the wet process which is common in pavement field is used to modify asphalt cement first and mix it with aggregates. Chelovian and Shafabakhsh used wet mixing method with kerosene solvent to produce the homogeneous bitumen mix. The quantity of base bitumen is heated at 150 C till it becomes fluid. Then gradually the amounts of 0.3%, 0.6%, 0.9%, and 1.2% nanoaluminum oxide (Al2O3) were dissolved in kerosene solvent and added to the base asphalt cement. The mixing period was 15 min using a high shear mixer at a speed of 4000 revolutions per minute (rpm). Then the required modified asphalt cement was ready to produce the asphalt samples (Chelovian and Shafabakhsh, 2017). Furthermore, Enieb and Diab produced a modified asphalt cement with nanosilica using the same technique (wet method) with a different temperature, speed, and time. Nearly 500 gm of the base asphalt cement was heated at 160 C and mixed with the nanosilica using a shear mixer at a rate of 2000 rpm for 1 h. Different concentrations of the nanosilica were added 2%, 4%, and 6% by weight of asphalt cement 500 gm. The base asphalt cement has been mixed under the same mixing conditions of modified asphalt cement to avoid any varying degree of aging between the unaged prepared samples during the mixing
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process (Enieb and Diab, 2017). The wet technique is also used in another study by Shaban et al. where the modification was conducted in the laboratory by the addition of 3%, 5%, and 7% by weight of asphalt cement (wt%). A Silverson high shear mixer was used in the mixing process of base asphalt cement and Al2O3 modified asphalt cement. The blending of both modifiers with asphalt cement was prepared by melting. The asphalt was oven-heated until it became fluid at 150 C, a Silverson high shear mixer was used to mix the materials at a constant temperature of 170 1 C at 5000 rpm for 90 min to ensure the production of homogeneous mixtures (Ali et al., 2017). Alhamali in another study used nanosilica to improve asphalt properties. Nanosilica was added gradually into the base asphalt cement at concentrations of 2%, 4%, and 6% by weight of the asphalt cement while mixing in the high shear machine. The asphalt cement samples were kept at 163 C and under the speed of 3000 rpm for 1 h (Alhamali et al., 2016). Hui Yao and Zhanping You used micro and nanomaterials modified asphalt mixture to evaluate the mechanical performance of asphalt mixtures. The micro and nanomaterials (2% and 4% MCF, 2% and 4% Nanomer, 4% and 6% NS, 2% and 4% NMN, and 2% and 4% PMN) were mixed with the base asphalt cement using a high shear mixer at a temperature of 140 C and a speed of 4000 rpm for 2 h. Then the modified asphalt cement was prepared for image testing and the evaluation of the performance (Yao and You, 2016). From the previous studies it is well known that the modification of asphalt cement to produce asphalt mixture samples using a wet mix technique ensures better performance and quality of asphalt mixtures while adding nanomaterials in the base asphalt cement using a dry method shows less influences on the performance of asphalt mixtures.
8.4 8.4.1
Materials and experimental design Materials
Two materials, a commercially available asphalt binder and Al2O3 nanoparticles, were used to produce a base and modified asphalt mixture in the laboratory. The base binder was 60/70 penetration grade (PG 69-19) asphalt obtained from the Port Klang Factory in Malaysia, while the nanomaterial (nanoscale aluminum oxide Al2O3 white powder) was supplied by Company in China. The physical properties of the base asphalt and Al2O3 nanoparticles are shown in Table 8.1.
8.4.2
Modified asphalt binders preparation
The blends were prepared by melting Al2O3 nanoparticles to produce three modified asphalt binders with 3, 5, and 7 wt% Al2O3 nanoparticles, in addition to one base asphalt sample as a control sample. The asphalt was oven-heated until it became fluid as desired (150e160 C). A Silverson high shear mixer was used to mix the materials at a constant temperature of 170 1 C at 5000 rpm for 90 min to ensure the production of homogeneous mixtures. The homogeneity of mixtures was evaluated using the
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Table 8.1 Physical properties of base asphalt and Al2O3 nanoparticles Material
Properties
Test method
Value
Asphalt 60/70
Specific gravity
ASTM D70
1.03
ASTM D5
70
ASTM D36
46.0
ASTM D4402
0.5
Ductility
ASTM D113
125
Size
e
13 nm
Form
e
White powder
Density
e
3.5e3.9
Penetration at
25 C
Softening point (C) Viscosity at Al2O3 nanoparticles
135 C
(Pa.s)
softening point test. The samples from the softening point test were taken every 30 min during a mixing duration of 2 h until the value of softening point became stable, and the sample can then be considered as a homogeneous mixture.
8.4.3
The design of aggregates
Six stockpiles of aggregates (19.00, 9.50, 4.75, 2.36, 0.30, and 0.075 mm) were used to produce the base and modified asphalt mixtures, where stockpiles were coarse aggregates and others were fine aggregates. The Superpave uses the nominal maximum aggregate size (NMAS) of the aggregate to categorize mixtures and define graduation requirements. In this study, the nominal maximum particle size was 19 mm. The aggregate generally within the Superpave mix deigns requirement. Therefore, it is suitable for usage to produce asphalt mixtures. Table 3.1 shows the test results of aggregate properties which defined the ideal aggregate as the aggregate which has proper particle size and grading, strong and tough, and consists of angular, the surface of the aggregate is clean and rough (Asphalt-Institute, 2007). However, selecting an aggregate material for use in asphalt mixtures also depends on the availability and cost of the material as well as the type of construction. Fig. 8.6 shows the sample of aggregate design for asphalt mixtures (dense-graded) used in this study (Table 8.2).
8.4.4
Determination of volumetric properties of asphalt mixtures
Asphalt mixtures were designed based on the Superpave methods. Once the aggregate and the asphalt cement grade are selected, trial samples are compacted in the laboratory at various asphalt cement contents above and below the expected optimum. Samples of asphalt mixtures were prepared at four different asphalt contents by weight of asphalt mix mass (5%, 5.5%, 6%, and 6.5%), with three replications per asphalt content.
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120
100
Passing (%)
80
60 Upper limit Restricted zone
40
Sample Lower limit
20
0
0
5
10 15 Seive size (mm)
20
25
Figure 8.6 Aggregate design of asphalt mixtures. Table 8.2 Aggregate properties test results Aggregate properties Flakiness (%)
Result (%) 6.00
Criteria
Standard
<20%
BS 812: Section 105.1
Fine aggregate angularity (%)
51.5
>45%
AASHTO T33
Elongation (%)
16.0
<20%
BS 812
Sand equivalent test
48.5
>45%
AASHTO 176
Los Angeles test (%)
32.13
<45%
ASTM C:131-81
Soundness test (%)
6.1
<12%
ASTM C88
Deleterious materials (%)
0.5
0.2%e10%
ASTM C142
For base asphalt cement and each modifier concentration, one asphalt cement content was chosen, which met the requirement of Superpave mix design 4% air voids. The results show that the optimum asphalt content (OAC) for base asphalt was 5.7% and OAC for ASA polymer modified asphalt mixtures was 5.9 for 3% ASA, 6% for 5% ASA, and 6.2% for 7% ASA, while OAC of Al2O3 nanoparticles modified asphalt mixtures was 5.81 for 3% Al2O3, 5.92 for 5% Al2O3, and 6.45% for 7% Al2O3. After the aggregate and asphalt reached the required mixing temperature, the samples were removed from the oven and mixed in the bucket until a uniform and complete coating of the aggregate is achieved. Then, the samples were placed into the oven for 2 h, to let the aggregates absorbed completely in the asphalt cement. The bulk specific gravity
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(Gmb) of the compacted mixtures should be determined before performance testing. The bulk specific gravity test consists of weighing the specimen in air and in water. In order to determine the volume of the specimen, including open voids in the surface, the mass is also determined after the specimen has been immersed in water and its surface blotted with a damp towel to dry the surface without removing the water in the surface voids. Also, the maximum theoretical specific gravity (Gmm) for the dry loose mixtures was performed according to ASTM D 2041 (Vavrik and Carpenter, 1998). In addition, the OAC should be within acceptable volumetric properties when the compacted specimens matched with 4% air voids. The OAC in this study was chosen for all asphalt mixtures (base and modified) independently based on volumetric properties which satisfy the criteria of the Superpave system.
8.5
Advantages and disadvantages of nanoparticles in the modification of asphalt mixtures
Using asphalt cement additives for highway construction project depends on many factors such as cost, construction ability, availability, and expected performance. Asphalt cement additives have been used to improve asphalt pavement performance as well as to reduce asphalt pavement distresses such as moisture damage, permanent deformation, and thermal fatigue cracking. The performance of modified asphalt pavement is expected to be more stable at warmer temperatures and more flexible at colder temperatures. Nanomaterials become a permanent part of the highway construction, and the degree of modification depends on the modifier property, nanocontent, and nature of the asphalt cement. The addition increment of nanoclay in base bitumen has increased the stiffness of the asphalt, which improves its ability to withstand the permanent deformation and increased the indirect tensile strength which leads to improving the aging resistance. Such improvements will increase the durability and the cycle life of the asphalt pavements, which will reduce the cost of maintenance and repairs, and also make the asphalt cement easy to work with in hot areas, since the viscosity has increased (Yang and Tighe, 2013). On the other hand, there are possibilities to have some disadvantages of nanomaterial modified pavement under low temperatures. Research conducted by Ghile in 2006 shows that the fatigue resistance of base asphalt cement at low-temperatures is better or higher than modified asphalt cement with nanoclay (Ghile, 2006). Regardless of the disadvantage of modified asphalt with nanomaterials, nanomaterials have many advantages such as decreasing the permanent deformation and reducing or delaying the effect of aging properties under different conditions. Also, nanomaterials modified asphalt can improve the tensile strength and the reduced moisture susceptibility (Goh et al., 2011). Reducing the moisture susceptibility is very important in cold regions because most of the asphalt paved roads are subjected to snow, which usually leads to damage of the pavements, and with modification of pavement by nanomaterials resulting in pavement less susceptible to moisture, a massive amount of energy and money would be saved from less maintenance.
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Characteristic and performance evaluation of nanoparticles modified asphalt mixtures
Asphalt mixtures design techniques attempt to balance the composition of aggregate and asphalt cement to achieve long-lasting performance in a roadway structure. It is identified that asphalt mixtures consist primarily of asphalt cement, mineral aggregates, and air. The primary purpose of mix design is to produce mixtures with high resistance to deformation and cracking. The properties of the produced mixtures depend on the physical and chemical properties of the used materials. Each of the component materials needs to be carefully selected and controlled to ensure that they are of suitable quality for the asphalt mixtures and the expected performance. The aggregate plays a significant role in mix designs or to produce asphalt mixtures. The aggregate should have proper particle size and grading, durable and tough, and consists of angular, the surface of the aggregate is clean and rough (AsphaltInstitute, 2007). However, selecting an aggregate material for use in asphalt mixtures design is also dependent on the availability and cost of the material as well as the type of road construction.
8.6.1
Influence of nanoparticles on resilient modulus of asphalt mixtures
Resilient modulus is the most critical variable to mechanistic design approaches for asphalt structures. It is the measure of asphalt response regarding dynamic stresses and corresponding strains. The main purpose of the resilient modulus test result analyses was to determine if the addition of nanoparticles brought any significant change in the stiffness properties of modified mixtures. Using of Al2O3 with a concentration of 3%, 5%, and 7% as a modifier of asphalt shows that as the temperature increases, resilient modulus decreases regardless of the modifier type and content. The base asphalt cement has the lowest resilient modulus with 3528 mPa among the mixtures, while 5% Al2O3 have the highest resilient modulus 5082 mPa compared with other modified asphalt mixture samples as shown in Fig. 8.7. The improvement in resilient modulus at 25 C for 5% Al2O3 is nearly 44%. The resilient modulus at 25 C showed an average reduction of 71%, 75%, and 73% for 3, 5, and 7% respectively. This leads to identifying that the resilient modulus value is affected by the modifier content and the temperature. The modified asphalt mixtures consistently exhibited higher resilient modulus values than the base asphalt mix. The increase in modifier content produces an enhancement in the elastic properties of the asphalt mixtures. Therefore, modified asphalt has improved the resilient modulus of asphalt mixtures compared to the base asphalt. This might be due to the higher viscosity which gives the mixes polymer properties that lead to better resilience properties. These results indicate that using modified asphalt cement produces asphalt mixtures with higher stiffness and thus higher load-bearing capacity. Moreover, modification of the asphalt mixture using nanosilica shows significant improvement, the additional increment of nanosilica in asphalt blends results in a
Performance of asphalt mixture with nanoparticles
Resilient modulus (mPa)
6000
5082
5000 4000
179
4230
4100 3528
3000 2000 1000 0 0% Al2O3
3% Al2O3
5% Al2O3
7% Al2O3
Modifier content (%)
Figure 8.7 Resilient modulus of the base and Al2O3 nanoparticles modified asphalt mixtures.
positive influence on the resilient modulus of the asphalt mixture (Enieb and Diab, 2017). The value of the resilient modulus has increased by increasing the content of the nanoparticles as shown in Fig. 8.8, which is consistent with previous research. Regardless of the type of binder and the test temperature Al2O3 shows better performance of asphalt mixture compared to nanosilica. It is noteworthy that the form of asphalt mixture was 60/70 penetration grade for both studies, but from different sources, while the test temperature varies, 20 C for Al2O3 and 25 C for nanosilica. Also, increase in resilient modulus of the modified mixtures led to expect mixtures with high elasticity and therefore better resistance to rutting than the base mixture. The results of resilient modulus of modified asphalt mixture using the same concentration of nanosilica 0%, 2%, and 4%, conducted at a temperature of 25 C, show higher improvement as the base asphalt cement was PG-76. The results of the resilient modulus tests are shown in Fig. 8.9. It is observed that the modified asphalt mixtures with 4% nanosilica have the lowest susceptibility to fatigue deformation with the 720
Resilient modulus (mPa)
720
690
700 680 660 625
640 620
600
600 580 560 540 0% NS
2% NS 4% NS Modifier content (%)
6% NS
Figure 8.8 Resilient modulus of nanosilica modified asphalt mixtures.
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Resilient modulus (mPa)
2500
2037
2000 1500
1624 1170
1000 500 0 0% NS
2% NS Modifier content (%)
4% NS
Figure 8.9 Resilient modulus of nanosilica modified asphalt mixtures.
highest resilient modulus of 2037 mPa, while the base sample as expected has the highest susceptibility to fatigue deformation with a low resilient modulus of 1170 mPa. It indicates that the addition of nanosilica is able to improve resistance to fatigue deformation at intermediate temperatures compared to the control sample (Yusoff et al., 2014). The modification of asphalt mixtures with nanoparticles has a significant influence on the resilient modulus of asphalt mixtures and is able to improve the resistance to fatigue to mitigate the pavement distress.
8.6.2
Effect of nanoparticles on dynamic creep
The load when applying to the surface of asphalt mixtures deforms although a majority of deformation will be recovered after the pressure is removed. This phenomenon is referred to the characteristics of asphalt which is identified as a visco-elastic material. However, a minute quantity of irrecoverable viscous deformation would remain in mixtures. With applying lots of load cycles, the slight amounts of deformation would be accumulated and eventually result in rutting in the surface of asphalt mixtures. Figs. 8.10 shows the results of dynamic creep modulus for unaged samples of base asphalt mixtures and Al2O3 nanoparticles modified asphalt mixtures at a temperature of 40 C and a load of 80 kPa. The results show that with increasing the modifier concentration, the stiffness increased up to 5% Al2O3. The 5% of both modifiers show the higher amount of resistance to rutting (high stiffness). Meanwhile, the base asphalt mixtures as expected recorded the lowest resistance to the deformation (low stiffness). Moreover, the 7% Al2O3 shows a decrease in the stiffness due to the agglomeration among the nanoparticles with increasing the percentage of nanoparticles in asphalt matrix (Ali et al., 2017). The results are in good agreement with previous studies conducted by Yusoff et al (Yusoff et al., 2014) and Chelovian and Shafabakhsh (Chelovian and Shafabakhsh, 2017). They investigated the influences of nanosilica on modified asphalt mixtures and found that the rutting depths of nanomaterials modified asphalt mixtures decreased compared to the base asphalt mixtures, and a reduction in rutting depth was noted for a higher percentage of nanomaterials in the asphalt mixtures.
Dynamic creep modulus (MPa)
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Figure 8.10 Dynamic creep modulus of modified asphalt mixtures with Al2O3.
8.6.3
Impact of nanoparticles on the rutting distress
Rutting depth (defromation in mm)
The rutting of asphalt mixtures has an essential effect on the performance of the asphalt for the period of lifetimes. Rutting not only decreases the useful service life of the pavement but also it might distress basic vehicle handling, which can be dangerous to road operators. The depth and rate of rutting depend on load and volume of truck traffic, tire pressure, temperature, construction practices, the thickness of asphalt, asphalt cement type, aggregate, and mixture properties. Besides, the primary contributing factors are traffic and high temperatures. Fig. 8.11 shows the results obtained during the wheel-tracking tests carried out for unaged samples of modified asphalt mixtures with Al2O3 nanoparticles. The combination of the asphalt cement with the modifier results in an enhancement in the resistance against deformations. The addition of the Al2O3 nanoparticles modified asphalt mixtures showed a reduction in the rutting in high temperatures (50 C). Besides, it can be noted clearly that the 5% concentration has better performance of rutting resistance and base asphalt mixtures show the lowest value in resistance to rutting; the use of 2.5
2.35 2
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Figure 8.11 Rut depth of Al2O3 nanoparticles modified asphalt mixtures.
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Al2O3 nanoparticles to modify base asphalt cement to produce asphalt mixtures is considerably more efficient than the use of base asphalt. This result is similar with the findings of other studies when using SBS and crumb rubber to modify asphalt mixtures as the increase of both modifiers leads to improvement in asphalt properties (Moreno-Navarro et al., 2014). Also, it is similar with a study conducted by Polacco et al. when they used sodium montmorillonite (Na-MMT) and organophilic montmorillonite (OMMT) nanoclay to modify asphalt mixtures. The results show that the modifications have promising potential to decrease the permanent deformation asphalt pavements (Polacco et al., 2008).
8.6.4
Influence of nanoparticles on moisture susceptibility
The breaking of the bond between asphalt and aggregate is identified as stripping, and the phenomenon that causes stripping between asphalt cement and aggregate mixtures is very complicated and not yet understood entirely (Xiao et al., 2010). The stripping will slowly decline the strength of the materials throughout the years which will be apparent as cracking, rutting, corrugation, traveling, shoving, etc. The procedure of performing to evaluate moisture susceptibility was based on AASHTO T283. This test is not a performance test, but it serves two purposes. First, it identifies whether a combination of asphalt cement and aggregate is moisture susceptible. Secondly, it measures the effectiveness of antistripping additives (Asphalt-Institute, 2007). Figs. 8.12 indicates that all asphalt mixtures regardless of modification have TSR values more than 80% criteria value according to AASHTO T283. A TSR of base asphalt mixtures is 85%. The addition of nanoparticles makes a significant improvement in the adhesion between the asphalt cement and aggregate. Merely the modifier gets into the spaces
99 100
97 93
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Figure 8.12 Moisture susceptibility of Al2O3 nanoparticles modified asphalt mixtures.
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between the aggregates, better coating the aggregates. Therefore, more resistance to moisture damage is provided. The TSR results show that the addition of nanoparticles leads to increase in the resistance to moisture susceptibility up to 5%. The 7% Al2O3 shows an improvement of 9%. Using nanosilica to modify asphalt mixtures shows similar results to that of Al2O3 nanoparticles which leads to reduce the susceptibility of asphalt mixtures to moisture damage; it was found that modified asphalt mixture samples achieved a higher TSR value compared with base asphalt mixtures.
8.7
Durability of modified asphalt mixtures
Aging of asphalt concrete affects the stiffness of the asphalt cement and may result in excessive stiffness. To be able to characterize asphalt concrete adequately requires that samples to be evaluated should be aged to simulate in-place properties of HMA (Hot Mix Asphalt) mixture. Aging in the field is significantly affected by the initial voids in the mix, the densification of the mixture under traffic, and the amount of heat applied to the mixture during production. Because of the rate of aging of asphalt cement in the mixture is affected by the mixture properties, such as in-place air voids, the entire mixture should be aged. The Superpave mix design requires that the mixture be at compaction temperature for 2 h after mixing and before compaction. This process simulates some initial aging, but primarily it allows for absorption of some of the asphalt cement into the aggregate. Superpave also developed a method to age the compacted mixture to simulate in-service aging in the field. This process involves placing the compacted samples in an oven for an extended period to allow for oxidation of asphalt cement. Aging is primarily associated with the loss of volatile components and oxidation of the asphalt during asphalt concrete construction which is known as short-term aging and progressive oxidation during service life in the field recognized as long-term aging. Asphalt, when it contacts with air (oxygen), oxidizes well gradually, increasing its viscosity resulting in harder asphalt with less flexibility. The value of viscosity is extremely dependent on the temperature, time, and the asphalt film thickness.
8.8
Challenges of nanoparticles modification
Asphalt pavement is one of the materials commonly used for roads and airports construction. The scientists and engineers are continually trying to enhance its performance. The surfaces of roads are subjected to numerous loadings of heavy axes and severe weather conditions, so the surfaces must have sufficient strength against cracking, fatigue, and creep resistance. The main purposes of characterization and modification of the physical, chemical, morphological, rheological, and mechanical properties of asphalt pavement are to overcome or mitigate its distress. It was found that the modification of asphalt cement using nanomaterials leads to improvement in the viscoelastic behavior of the asphalt and changes its rheological
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properties. Also, the act of nanomaterials inside the asphalt matrix is not fully understood, and more studies should be carried out to investigate the chemical properties which are the most important properties in the field of nanomaterials modified asphalt cement. One of the greatest challenges that face the researchers is identifying the proper way and time to mix nanomaterials with base asphalt mixtures. Also, the speed of mixing plays a big role in the uniform dispersion of nanomaterials, the uniform dispersion of the modifiers inside the blends results in a good estimation of the behavior of asphalt mixtures. Moreover, some researchers use an ultrasonic machine or chemical solvate to ensure that the nanoparticles will not be agglomerated during the mixing process.
8.9
Conclusion
The main objectives of this research were to characterize the mechanical properties of modified asphalt mixtures. The addition of a modifier to the base asphalt mixture is able to improve the viscoelastic behavior of the asphalt and change its rheological properties. One of the types of modifiers used is nanoaluminum oxide (Al2O3), which has a different amount of influence, decreasing or increasing, on the mechanical properties of the asphalt mixture. After conducting laboratory tests on asphalt mixtures with different nanoparticles content and after analyzing the data and comparing the results, the following conclusions are drawn: 1. It was found that the modified asphalt mixtures by Al2O3 consistently exhibited higher resilient modulus values than the base asphalt mixtures and the 5% concentration for both modifiers has the highest value. The increase in modifier content produces an enhancement in the elastic properties of the asphalt mixtures. Therefore, modified asphalt has improved the resilient modulus of asphalt mixtures compared to the base asphalt. 2. Evaluation of dynamic creep among the base asphalt mixtures and modified asphalt mixtures shows that the modifier has a significant influence to improve the resistance to permanent deformation of base asphalt mixture and 5% concentration of the modifier has the lowest permanent deformation while the base mixture has the highest deformation among the mixes. 3. The modified mixtures have good resistance to rutting compared with the base asphalt mixture which has the lowest resistance to rutting. Also, 5% of modifier shows the highest performance of asphalt mixture among the mixtures. 4. The TSR results indicate that the modified samples have slightest susceptibility to moisture damage than modified samples with Al2O3 nanoparticles, meanwhile the base asphalt cement is more susceptible to moisture damage. Moreover, the 7% concentration shows the highest improvement, which might be due to that the behavior of Al2O3 is acting differently with the presence of water or due to some chemical reactions.
Acknowledgments The Ministry of Science has supported part of this work, Technology and Innovation (MOSTI), Malaysia for research funding through project 03-01-02-SF0999.
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References Abdullah, M., Zamhari, K., Nayan, N., Hainin, M., Hermadi, M., 2012. Physical properties and storage stability of asphalt binder modified with nanoclay and warm asphalt additives. World Journal of Engineering 9 (2), 155e160. Alhamali, D.I., Wu, J., Liu, Q., Hassan, N.A., Yusoff, N.I.Md, Ali, S.I.A., 2016. Physical and rheological characteristics of polymer modified Bitumen with nanosilica particles. Arabian Journal for Science and Engineering 41 (4), 1521e1530. Ali, S.I.A., Ismail, A., Karim, M.R., Yusoff, N.I.Md, Al-Mansob, R.A., Aburkaba, E., 2017. Performance evaluation of Al2O3 nanoparticle-modified asphalt binder. Road Materials and Pavement Design 18 (6), 1251e1268. Amirkhanian, A.N., Xiao, F., Amirkhanian, S.N., 2011. Characterization of unaged asphalt binder modified with carbon nanoparticles. International Journal of Pavement Research and Technology 4 (5), 281e286. Asphalt-Institute, 2007. Asphalt Handbook 7th Edition, seventh ed. USA: Asphalt Institute. Chelovian, A., Shafabakhsh, G., 2017. Laboratory evaluation of Nano Al2O3 effect on dynamic performance of stone mastic asphalt. International Journal of Pavement Research and Technology 10 (2), 131e138. Chong, K.P., 2004. Nanoscience and engineering in mechanics and materials. Journal of Physics and Chemistry of Solids 65 (8), 1501e1506. El-Shafie, M., Ibrahim, I.M., El Rahman, A.M.M.A., 2012. The addition effects of macro and nano clay on the performance of asphalt binder. Egyptian Journal of Petroleum 21 (2), 149e154. Enieb, M., Diab, A., 2017. Characteristics of asphalt binder and mixture containing nanosilica. International Journal of Pavement Research and Technology 10 (2), 148e157. Ghile, D.B., 2006. Effects of Nanoclay Modification on the Rheology of Bitumen and on Performance of Asphalt Mixtures. Delft University of Technology, Delft, The Netherlands. Goh, S.W., Akin, M., You, Z., Shi, X., 2011. Effect of deicing solutions on the tensile strength of micro-or nano-modified asphalt mixture. Construction and Building Materials 25 (1), 195e200. Ja, S.G.A.F.O., Hromi, S.R.T., 2013. Nanoclay-modified asphalt mixtures for eco-efficient construction. Nanotechnology in Eco-Efficient Construction: Materials, Processes and Applications 108. Jahromi, S.G., Khodaii, A., 2009. Effects of nanoclay on rheological properties of bitumen binder. Construction and Building Materials 23 (8), 2894e2904. Khattak, M.J., Khattab, A., Rizvi, H.R., Zhang, P., 2012. The impact of carbon nano-fiber modification on asphalt binder rheology. Construction and Building Materials 30, 257e264. Kreyling, W.G., Semmler-Behnke, M., Chaudhry, Q., 2010. A complementary definition of nanomaterial. Nano today 5 (3), 165e168. Lazzara, G., Milioto, S., 2010. Dispersions of nanosilica in biocompatible copolymers. Polymer Degradation and Stability 95 (4), 610e617. Mahshid, S., Mahshid, S.S., Askari, M., Dolati, A., Yang, L., Luo, S., Cai, Q., 2012. Enhanced electrocatalytic activity of TiO2 nanotubes modified with Pt and Pd nanoparticles: electrooxidation of dopamine, uric acid, and ascorbic acid. Journal ISSN 1929, 1248. Moreno-Navarro, F., Sol-Sanchez, M., Rubio-Gamez, M.C., Segarra-Martínez, M., 2014. The use of additives for the improvement of the mechanical behavior of high modulus asphalt mixes. Construction and Building Materials 70, 65e70.
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Motlagh, A.A., Kiasat, A., Mirzaei, E., Birgani, F.O., 2012. Bitumen modification using carbon nanotubes. World Applied Sciences Journal 18 (4), 594e599. Peralta, J., Hugo, M.R.D.S., Machado, A.V., 2010. High-performance asphalt pavements are incorporating recycled polymers as aggregates and binder modifier. Technology 77, 192e200. Polacco, G., Kríz, P., Filippi, S., Stastna, J., Biondi, D., Zanzotto, L., 2008. Rheological properties of asphalt/SBS/clay blends. European Polymer Journal 44 (11), 3512e3521. Rana, A.K., Rana, S.B., Kumari, A., Kiran, V., 2009. The significance of nanotechnology in construction engineering. International Journal of Recent Trends in Engineering 1 (4), 46e48. Santagata, E., Baglieri, O., Tsantilis, L., Chiappinelli, G., Aimonetto, Brignone, I., 2015. Effect of sonication on high-temperature properties of bituminous binders reinforced with nanoadditives. Construction and Building Materials 75, 395e403. Santagata, E., Baglieri, O., Tsantilis, L., Dalmazzo, D., 2012. Rheological characterization of bituminous binders modified with carbon nanotubes. Procedia-Social and Behavioral Sciences 53, 546e555. Saoula, S., Mokhtar, K.A., Haddadi, S., Ghorbel, E., 2009. Improvement of the performances of modified bituminous concrete with EVA and EVA-waste. Physics Procedia 2 (3), 1319e1326. Vavrik, W., Carpenter, S., 1998. Calculating air voids at specified number of gyrations in Superpave gyratory compactor. Transportation Research Record: Journal of the Transportation Research Board 1630, 117e125. Xiao, F., Zhao, W., Gandhi, T., Amirkhanian, S.N., 2010. Influence of antistripping additives on moisture susceptibility of warm mix asphalt mixtures. Journal of Materials in Civil Engineering 22 (10), 1047e1055. Yang, J., Tighe, S., 2013. A review of advances in nanotechnology in asphalt mixtures. Procedia-Social and Behavioral Sciences 96, 1269e1276. Yao, H., You, Z., 2016. The effectiveness of micro-and nanomaterials in asphalt mixtures through dynamic modulus and rutting tests. Journal of Nanomaterials 2016, 10. Yao, H., You, Z., Li, L., Goh, S.W., Lee, C.H., Yap, Y.K., Shi, X., 2013. Rheological properties and chemical analysis of nanoclay and carbon microfiber modified asphalt with Fourier transform infrared spectroscopy. Construction and Building Materials 38, 327e337. Yasmin, A., Luo, J.J., Abot, J.L., Daniel, I.M., 2006. The mechanical and thermal behavior of clay/epoxy nanocomposites. Composites Science and Technology 66 (14), 2415e2422. You, Z., Mills-Beale, J., Foley, J.M., Roy, S., Odegard, G.M., Dai, Q., Goh, S.W., 2011. Nanoclay-modified asphalt materials: preparation and characterization. Construction and Building Materials 25 (2), 1072e1078. Yusoff, N.I.Md, Breem, A.A.S., Alattug, H.N.M., Hamim, A., Ahmad, J., 2014. The effects of moisture susceptibility and ageing conditions on nano-silica/polymer-modified asphalt mixtures. Construction and Building Materials 72, 139e147. Zare-Shahabadi, A., Shokuhfar, A., Ebrahimi-Nejad, S., 2010. Preparation and rheological characterization of asphalt binders reinforced with layered silicate nanoparticles. Construction and Building Materials 24 (7), 1239e1244.
8
Shaban Ali Zangena Civil Engineering Department, Faculty of Civil and Environmental Engineering, Near East University, Turkey
8.1
Introduction
The asphalt cement and asphalt mixtures need to be improved to reduce and prevent distresses. Polymers became a part of the materials used by humans in a lot of applications than any other categories of materials available, therefore to improve the properties of bitumen in the present world, polymers are used as additives to enhance asphalt cement and asphalt mixture properties because of their excellent physical and chemical properties. Polymers can be defined as large molecules composed of a large number of correlations of small particles with each other, and these small molecules are called monomers. Furthermore, there are six main thermoplastic polymers: polyvinyl chloride (PVC), polystyrene (PS), low-density polyethylene (LDPE), high-density polyethylene elements, and compounds in waste plastic such as copolymers, elastomers, and plastomers. Using an EVA polymer to investigate the mechanical behavior of the asphalt mixtures showed the highest resistance constant to deformation damage. The EVA polymer is one of the best solutions to improve the physical and mechanical properties of bitumen concrete as well as an excellent way to combat (principally rutting) permanent deformation damage (Saoula et al., 2009). Polymer modified asphalt (PMA) based on conventional tests and rheological properties with an increasing polymer content shows a significant increase in mechanical properties. On the other hand, rheological properties of PMBs represented higher complex modulus (G*) especially at high temperature and increased elastic properties of PMB at low frequency. Combination of polymers provides an opportunity to be reused and recycled and at the same time allows the possibility of maintaining sources as well as reduces the costs. On the other side, the combination of polymers successfully improved the performance and properties of asphalt (Peralta et al., 2010). The effectiveness of polymer concentration on the microstructure, thermal, and rheological properties using recycled polyethylene modified bitumen comes out with significant modification of the rheological reaction. Recycled polyethylene (RPE) polymer increases the principles of viscosity and storage as well as causes a decrease in thermal susceptibility. As a result, asphalt cement modification with RPE yields improved mechanical characteristics, thus higher resistance to rutting and also to fatigue and thermal cracking (Peralta et al., 2010). Once polymers are added to the asphalt, sometimes or in some cases, the
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separation occurs between polymers and asphalt which results in poor adhesion between binder and aggregates with time, so nanotechnology appeared to be another solution to improve asphalt quality. Nanotechnology has recently become one of the attractive research fields in civil engineering and construction materials. Conventionally, it has led to advances in the areas of materials science, microelectronics, and medicine. However, several developments in nanotechnology may be applied to the field of construction engineering (Rana et al., 2009). The manufacture of new materials at the molecular level on the nanoscale leads to phenomena associated with atomic and molecular interactions to strongly affect the materials’ macroscopic properties (Chong, 2004). Nanoscale modification improves some characteristics of asphalt binders and asphalt mixtures, such as rutting and fatigue, but more investigations are required before it can be applied on a large scale (Khattak et al., 2012). As the nanotechnology is a creation of new materials and engineers are interested in studying the material properties at the level of macro and nanoscales, the nano and microscales afford fundamental insights into the development of science and technology. Fig. 8.1 shows the development of length scales of the asphalt material (You et al., 2011). Nanotechnology includes microscopic particles of a material; nanomaterials are new materials that recently become popular and one of the large and important parts in research and development worldwide, they are also defined as microscale fillers which would make polymers efficient as filler reinforcements (Mahshid et al., 2012). The obtained results from the modification of nanomaterials show improvement in mechanical behavior properties of asphalt mixtures, such as fatigue resistance, indirect tensile strength, and creep. Polymer based nanocomposites reinforced with montmorillonite nanoclay particles have drawn substantial interest; this is according to the fact that these types of composites show significant enhancements in thermal and mechanical properties compared to the virgin polymer. Also, many studies with the considerable nanocomposites show substantial improvements in strength and stiffness compared with those modified by polymer only, even by adding a small quantity of nanomaterial particles (Yasmin et al., 2006).
8.2 8.2.1
Types of nanoparticles modified asphalt mixture Nanoclay modified asphalt
The definition of nanoclay is clay that can be modified to make the clay complexes compatible with organic monomers and polymers. The common clays are occurring minerals and thus subjected to natural variation in their formation. The pureness of the clay plays a significant role in affecting the properties of the nanocomposite, and clay contains aluminaesilicates, which have a layered structure. It also includes silica SiO4 tetrahedron bonded to alumina AlO6 octahedron in several ways. Related to results of plastic limit is between the ranges of 85.4 up to 87.5%. The process of the nanoclay material is displayed in Fig. 8.2 (Jahromi and Khodaii, 2009).
Meso
Micro
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Quantum
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10–12
Aggregate Asphalt
100
10–3
10–6
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Figure 8.1 Development of length scales of asphalt. Source: You, Z., Mills-Beale, J., Foley, J.M., Roy, S., Odegard, G.M., Dai Q.,, Goh S.W., 2011. Nanoclay-modified asphalt materials: preparation and characterization. Construction and Building Materials 25 (2), 1072e1078.
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Figure 8.2 Nanoclay surface ttreatment. Source: Jahromi, S.G., Khodaii, A., 2009. Effects of nanoclay on rheological properties of bitumen binder. Construction and Building Materials 23 (8), 2894e2904.
Currently, several studies have been conducted to evaluate the effect of nanoclay particles on the performance of asphalt cement and several studies have been using the concentration of 2%e6%, and some researchers used up to 8% by weight of the asphalt cement. Jahromi and Khodaii (2009) evaluated the nanoclay effects on rheological properties of asphalt cement, the concentration of the modifier was 2, 4, and 7 wt%. The base asphalt cement was 60/70 penetration grade. Tests proved that the modifications of asphalt using nanoclay are able to increase the stiffness of the modified asphalt and delay the aging. It is observed that when asphalt was modified with a slight quantity of nanoclay, it successfully enhances the physical properties of asphalt. Moreover, the nanoclay materials have a higher aspect ratio and a huge surface area, and their particles are uniform in size and arrangement. Then, a small percentage of nanoclay modified asphalt cement able to change the rheological properties shows a decline of penetration, ductility, and an increase in softening point and aging resistance. DSR results also revealed that the sheer complex modulus (G*) increases with decreasing the temperature or increasing frequency, while the phase angle increases as the temperature increases or frequency decreases. Also, the temperature susceptibility of modified asphalt cement was reduced compared to the base asphalt cement, the results of the study show that the addition of the nanoclay had a good influence on the internal structure of the mixtures and, therefore, affects their
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rheological behavior (Jahromi and Khodaii, 2009). Zare-Shahabadi et al. used the organically modified bentonite (OBT) and bentonite clay (BT) to modified asphalt cement (60/70 penetration grade) with the addition of 1, 2, 4, 5, and 6 wt%, to investigate the physical properties and high temperature, dynamic rheological performance of the BT and OBT modified asphalt cement. Further, to evaluate the properties of low-temperature cracking of the modified asphalt cement after artificial short and long-term aging, they found that the OBT and BT modified asphalts have shown an increase in softening point and viscosity better than the base asphalt cement. Nonetheless, the ductility of the modified asphalt cement decreased with the addition of OBT and BT. Evaluation of dynamic rheological properties shows that the modified asphalt cement was better than the base asphalt cement and shows an increase in complex modulus and decrease in the phase angle which indicates that the rutting resistance of the modified asphalts was enhanced. Also, it is observed in the bending beam rheometer (BBR) test that creep stiffness was reduced. As a result, the resistance of low-temperature cracking was improved (Zare-Shahabadi et al., 2010). El-Shafie et al. (2012) investigated influences of macro and organically modified nanoclay on the properties of asphalt cement using local asphalt cement of penetration grade 60/70, a high-shear mixer was used to produce the asphalt nanocomposite at 160 C. Nanoclay was added to asphalt cement with concentrations of 2, 4, 6, and 8 wt%. The results revealed that the physical and mechanical properties of modified asphalt are significantly enhanced as the penetration decreases up to 25%, meanwhile the softening point increases up to 12 C compared to the base asphalt. The best asphalt performance was observed when the addition of nanoclay was 6% (El-Shafie et al., 2012). Abdullah et al. (2012) studied the physical properties and evaluated storage stability of the local asphalt modified with nanoclay and warm asphalt additives (WAA). The outcomes of the research showed that the modified asphalts had good storage stability; also they can improve the physical properties of asphalt, as the softening point increased and the penetration decreased. Moreover, a better decline of mixing and compaction of asphalt mixtures was observed (Abdullah et al., 2012). Yao et al. (2013) worked to investigate the rutting and fatigue resistance performance as well as changes in the microstructure of modified asphalt binders using the DSR and FTIR tests. The base asphalt cement was PG 58-34 modified with the acrylonitrile butadiene styrene (ABS). The materials used in this investigation were (A) nanometer nanoclay (NI.44P), (B) carbon microfibers (MCF), (C) nonmodified nanoclay (NMN), and (D) polymer modified nanoclay (PMN) as shown in Fig. 8.3. The concentrations of 2 and 4 wt% were added to the base asphalt. It was found that from the preparation and mixing of nano and micromodified asphalt, it is realized that the nano or micromaterials might have physical dispersion and chemical reactions with the base asphalt. Based on the DSR outcomes, the addition of all modifiers was able to increase the complex shear modulus compared to the base asphalt cement, and also improved the resistance to rutting. Results of FTIR spectroscopy show the addition
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Figure 8.3 SEM images of (A) nanometer nanoclay, (B) carbon microfibers, (C) nonmodified nanoclay, and (D) polymer modified nanoclay. Source: Yao, H., You, Z., Li, L., Goh, S.W., Lee, C.H., Yap, Y.K., Shi, X., 2013. Rheological properties and chemical analysis of nanoclay and carbon microfiber modified asphalt with Fourier transform infrared spectroscopy. Construction and Building Materials 38, 327e337.
of ultrafine materials in the asphalt cement, the oxidation response may be declining in the modified asphalt cement once it is exposed to heat and sunlight. Concisely, the consequence of modified asphalt on antioxidation enhanced when some ultrafine materials were added to the base asphalt (Yao et al., 2013). Santagata et al. (2015) evaluated the effects of sonication on high-temperature properties of base asphalt binder which is classified as a PG58-22 modified with nanoclay (NCA and NCB) and carbon nanotubes (CNT) investigated. Evaluation of the impacts of additives shows that the best resistance to rutting was found with using CNT and NCA, but the NCB displays a much lower capability to affect the rheological properties of base asphalt cement (Santagata et al., 2015). Ja and Hromi (2013) investigated the impact of nanoclay modified asphalt mixtures with concentrations of 0.2%, 0.4%, and 0.7% by weight of asphalt cement (60/70 penetration grade). Performed tests on dense asphalt mixtures indicate that the modifications using Cloisite-15A and Nanofill-15 increase the stiffness of modified asphalt mixtures and lead to improvements in the rutting resistance, resilient modulus, Marshall Stability, and indirect tensile strength. It is also noted that fatigue performance enhanced at low temperatures (Ja and Hromi, 2013).
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Nanosilica modified asphalt cement
One of the most abundant compound materials on earth is silica, it is mostly employed in manufacturing to produce colloidal silica, silica gels, and fumed silica. Worldwide, silica nanoparticles have been used in several industries such as medicine and engineering. Currently, silica nanocomposites become one of the conventional materials in the modification of asphalt cement and asphalt mixtures, it might be because of the low cost of manufacture and the high-performance structures of these nanomaterials (Lazzara and Milioto, 2010). Nanosilica particles have been used in many applications of civil engineering, starting from application of cement and cement composites to application of polymers and modification of asphalt cement. Fig. 8.4 shows a SEM image of nanosilica. Application of nanosilica modified asphalt cement shows better performance of asphalt cement and asphalt mixtures. Yao et al. (2013) investigated the rheological properties and chemical bonding of nanosilica modified base asphalt cement (PG 58-34). The asphalt was modified with acrylonitrile butadiene styrene (ABS) with a concentration of 4 and 6 wt% and depending on the results, they found that with an additional increase in the concentration of nanosilica in the base asphalt cement, the viscosity decreased slightly for modified asphalt cement. The complex modulus of modified asphalt cement decreases slightly compared to the base asphalt. Also, modified asphalt cement has good resistance to high-temperature rutting compared to the base asphalt cement or aging process samples. The Scanning Electron Microscopy (SEM) images observe that there are some changes in the microstructure of modified asphalt cement compared to the base asphalt cement. Also, they show that nanosilica particles have a good dispersion in the asphalt cement. Finally, the dynamic modulus of the modified asphalt mixture increases significantly compared to the unmodified asphalt mixture and the concentration of 6% has higher dynamic modulus than 4% at elevated temperatures. These indicate
Figure 8.4 SEM image of nanosilica at 3,000 magnification. Source: Kreyling et al., 2010.
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that the nanosilica modified asphalt mixture was able to enhance the rutting resistance (Yao et al., 2013).
8.2.3
Carbon nanotubes modified asphalt cement
Carbon nanotubes as shown in Fig. 8.5 are produced from pieces of graphite that have rolled up to form a tubular structure, various techniques were used to produce carbon nanotubes, the common two methods are using electricity and an inert gas in an enclosed chamber (Amirkhanian et al., 2011). As there is a need to improve the properties of asphalt cement, several studies have been conducted in application nanotechnology using carbon nanotubes. Amirkhanian et al. (2011) presented a study on the description of unaged asphalt cement modified with percentages of 0.2%, 0.5%, 1.0%, and 1.5% by weight of asphalt cement of carbon nanoparticles using PG 64-22 from three sources. The results show that the addition of nanoparticles increased the viscosity values of asphalt cement. However, at a low concentration of nanoparticles (0.2%) the increase is not significant, which might be because the modified blends are similar to the base asphalt. Meanwhile, the higher viscosity values were observed obviously with a concentration of 1.0% and 1.5% nanoparticles modified asphalt cement. Moreover, the addition of the modifier improves the resistance of rutting at high service temperatures, and a higher failure temperature was noted in modified asphalt cement with a high concentration of the modifier. Santagata et al. (2012) used the carbon nanotubes in asphalt application, using base asphalt cement 50/70 penetration grade and carbon nanotubes as a modifier; some carbon nanotubes modified asphalt cement blends were prepared at different
Figure 8.5 SEM images of carbon nanoparticles. Source: Amirkhanian, A.N., Xiao F., Amirkhanian, S.N., 2011. Characterization of unaged asphalt binder modified with carbon nanoparticles. International Journal of Pavement Research and Technology 4(5), 281e286.
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concentrations (0.1, 0.5, and 1.0 wt%). The rheological characterization was evaluated in different aging conditions: unaged, short-term aging using RTFOT, and long-term aging with PAV. From viscosity test results, an increase in viscosity with the addition of carbon nanotubes concentration can be observed. Specifically, viscosity improvements were of the order of 9% for the 0.1% carbon nanotubes and 25% for the order of 0.5% carbon nanotubes as well as up to 80% with 1% of carbon nanotubes, which has higher improvement among the blends. Besides, the analysis of results of frequency sweep test carried out on the mixtures shows that adding a high amount of carbon nanotubes results in a significant enhancement in stiffness and elasticity at high temperatures and low frequencies, thus they have beneficial impacts on the potential rutting resistance (Santagata et al., 2012). Motlagh et al. (2012) investigated the physical properties of asphalt cement using carbon nanotubes as a modifier of the base asphalt cement (60/70 penetration grade). The results show that the penetration decreased and softening point increased with the addition of modifiers. With increase in the carbon nanotube concentration it is found that the ductility increases much more than the base asphalt, which means the modified asphalt cement is more adhesive than unmodified asphalt (Motlagh et al., 2012).
8.3
Laboratory techniques for preparation of nanoparticles modified asphalt mixtures
There are three conventional materials used in the preparation of modified asphalt mixtures in the laboratory namely, asphalt cement, aggregates, and the modifier (nanomaterials), also there are different types of base asphalt cement which play a significant role in the properties of modified asphalt mixtures. The methods that are used to modify asphalt cement are usually two ways dry method which are used in the modification of asphalt mixtures by adding additives as fillers, while the wet process which is common in pavement field is used to modify asphalt cement first and mix it with aggregates. Chelovian and Shafabakhsh used wet mixing method with kerosene solvent to produce the homogeneous bitumen mix. The quantity of base bitumen is heated at 150 C till it becomes fluid. Then gradually the amounts of 0.3%, 0.6%, 0.9%, and 1.2% nanoaluminum oxide (Al2O3) were dissolved in kerosene solvent and added to the base asphalt cement. The mixing period was 15 min using a high shear mixer at a speed of 4000 revolutions per minute (rpm). Then the required modified asphalt cement was ready to produce the asphalt samples (Chelovian and Shafabakhsh, 2017). Furthermore, Enieb and Diab produced a modified asphalt cement with nanosilica using the same technique (wet method) with a different temperature, speed, and time. Nearly 500 gm of the base asphalt cement was heated at 160 C and mixed with the nanosilica using a shear mixer at a rate of 2000 rpm for 1 h. Different concentrations of the nanosilica were added 2%, 4%, and 6% by weight of asphalt cement 500 gm. The base asphalt cement has been mixed under the same mixing conditions of modified asphalt cement to avoid any varying degree of aging between the unaged prepared samples during the mixing
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process (Enieb and Diab, 2017). The wet technique is also used in another study by Shaban et al. where the modification was conducted in the laboratory by the addition of 3%, 5%, and 7% by weight of asphalt cement (wt%). A Silverson high shear mixer was used in the mixing process of base asphalt cement and Al2O3 modified asphalt cement. The blending of both modifiers with asphalt cement was prepared by melting. The asphalt was oven-heated until it became fluid at 150 C, a Silverson high shear mixer was used to mix the materials at a constant temperature of 170 1 C at 5000 rpm for 90 min to ensure the production of homogeneous mixtures (Ali et al., 2017). Alhamali in another study used nanosilica to improve asphalt properties. Nanosilica was added gradually into the base asphalt cement at concentrations of 2%, 4%, and 6% by weight of the asphalt cement while mixing in the high shear machine. The asphalt cement samples were kept at 163 C and under the speed of 3000 rpm for 1 h (Alhamali et al., 2016). Hui Yao and Zhanping You used micro and nanomaterials modified asphalt mixture to evaluate the mechanical performance of asphalt mixtures. The micro and nanomaterials (2% and 4% MCF, 2% and 4% Nanomer, 4% and 6% NS, 2% and 4% NMN, and 2% and 4% PMN) were mixed with the base asphalt cement using a high shear mixer at a temperature of 140 C and a speed of 4000 rpm for 2 h. Then the modified asphalt cement was prepared for image testing and the evaluation of the performance (Yao and You, 2016). From the previous studies it is well known that the modification of asphalt cement to produce asphalt mixture samples using a wet mix technique ensures better performance and quality of asphalt mixtures while adding nanomaterials in the base asphalt cement using a dry method shows less influences on the performance of asphalt mixtures.
8.4 8.4.1
Materials and experimental design Materials
Two materials, a commercially available asphalt binder and Al2O3 nanoparticles, were used to produce a base and modified asphalt mixture in the laboratory. The base binder was 60/70 penetration grade (PG 69-19) asphalt obtained from the Port Klang Factory in Malaysia, while the nanomaterial (nanoscale aluminum oxide Al2O3 white powder) was supplied by Company in China. The physical properties of the base asphalt and Al2O3 nanoparticles are shown in Table 8.1.
8.4.2
Modified asphalt binders preparation
The blends were prepared by melting Al2O3 nanoparticles to produce three modified asphalt binders with 3, 5, and 7 wt% Al2O3 nanoparticles, in addition to one base asphalt sample as a control sample. The asphalt was oven-heated until it became fluid as desired (150e160 C). A Silverson high shear mixer was used to mix the materials at a constant temperature of 170 1 C at 5000 rpm for 90 min to ensure the production of homogeneous mixtures. The homogeneity of mixtures was evaluated using the
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Table 8.1 Physical properties of base asphalt and Al2O3 nanoparticles Material
Properties
Test method
Value
Asphalt 60/70
Specific gravity
ASTM D70
1.03
ASTM D5
70
ASTM D36
46.0
ASTM D4402
0.5
Ductility
ASTM D113
125
Size
e
13 nm
Form
e
White powder
Density
e
3.5e3.9
Penetration at
25 C
Softening point (C) Viscosity at Al2O3 nanoparticles
135 C
(Pa.s)
softening point test. The samples from the softening point test were taken every 30 min during a mixing duration of 2 h until the value of softening point became stable, and the sample can then be considered as a homogeneous mixture.
8.4.3
The design of aggregates
Six stockpiles of aggregates (19.00, 9.50, 4.75, 2.36, 0.30, and 0.075 mm) were used to produce the base and modified asphalt mixtures, where stockpiles were coarse aggregates and others were fine aggregates. The Superpave uses the nominal maximum aggregate size (NMAS) of the aggregate to categorize mixtures and define graduation requirements. In this study, the nominal maximum particle size was 19 mm. The aggregate generally within the Superpave mix deigns requirement. Therefore, it is suitable for usage to produce asphalt mixtures. Table 3.1 shows the test results of aggregate properties which defined the ideal aggregate as the aggregate which has proper particle size and grading, strong and tough, and consists of angular, the surface of the aggregate is clean and rough (Asphalt-Institute, 2007). However, selecting an aggregate material for use in asphalt mixtures also depends on the availability and cost of the material as well as the type of construction. Fig. 8.6 shows the sample of aggregate design for asphalt mixtures (dense-graded) used in this study (Table 8.2).
8.4.4
Determination of volumetric properties of asphalt mixtures
Asphalt mixtures were designed based on the Superpave methods. Once the aggregate and the asphalt cement grade are selected, trial samples are compacted in the laboratory at various asphalt cement contents above and below the expected optimum. Samples of asphalt mixtures were prepared at four different asphalt contents by weight of asphalt mix mass (5%, 5.5%, 6%, and 6.5%), with three replications per asphalt content.
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120
100
Passing (%)
80
60 Upper limit Restricted zone
40
Sample Lower limit
20
0
0
5
10 15 Seive size (mm)
20
25
Figure 8.6 Aggregate design of asphalt mixtures. Table 8.2 Aggregate properties test results Aggregate properties Flakiness (%)
Result (%) 6.00
Criteria
Standard
<20%
BS 812: Section 105.1
Fine aggregate angularity (%)
51.5
>45%
AASHTO T33
Elongation (%)
16.0
<20%
BS 812
Sand equivalent test
48.5
>45%
AASHTO 176
Los Angeles test (%)
32.13
<45%
ASTM C:131-81
Soundness test (%)
6.1
<12%
ASTM C88
Deleterious materials (%)
0.5
0.2%e10%
ASTM C142
For base asphalt cement and each modifier concentration, one asphalt cement content was chosen, which met the requirement of Superpave mix design 4% air voids. The results show that the optimum asphalt content (OAC) for base asphalt was 5.7% and OAC for ASA polymer modified asphalt mixtures was 5.9 for 3% ASA, 6% for 5% ASA, and 6.2% for 7% ASA, while OAC of Al2O3 nanoparticles modified asphalt mixtures was 5.81 for 3% Al2O3, 5.92 for 5% Al2O3, and 6.45% for 7% Al2O3. After the aggregate and asphalt reached the required mixing temperature, the samples were removed from the oven and mixed in the bucket until a uniform and complete coating of the aggregate is achieved. Then, the samples were placed into the oven for 2 h, to let the aggregates absorbed completely in the asphalt cement. The bulk specific gravity
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(Gmb) of the compacted mixtures should be determined before performance testing. The bulk specific gravity test consists of weighing the specimen in air and in water. In order to determine the volume of the specimen, including open voids in the surface, the mass is also determined after the specimen has been immersed in water and its surface blotted with a damp towel to dry the surface without removing the water in the surface voids. Also, the maximum theoretical specific gravity (Gmm) for the dry loose mixtures was performed according to ASTM D 2041 (Vavrik and Carpenter, 1998). In addition, the OAC should be within acceptable volumetric properties when the compacted specimens matched with 4% air voids. The OAC in this study was chosen for all asphalt mixtures (base and modified) independently based on volumetric properties which satisfy the criteria of the Superpave system.
8.5
Advantages and disadvantages of nanoparticles in the modification of asphalt mixtures
Using asphalt cement additives for highway construction project depends on many factors such as cost, construction ability, availability, and expected performance. Asphalt cement additives have been used to improve asphalt pavement performance as well as to reduce asphalt pavement distresses such as moisture damage, permanent deformation, and thermal fatigue cracking. The performance of modified asphalt pavement is expected to be more stable at warmer temperatures and more flexible at colder temperatures. Nanomaterials become a permanent part of the highway construction, and the degree of modification depends on the modifier property, nanocontent, and nature of the asphalt cement. The addition increment of nanoclay in base bitumen has increased the stiffness of the asphalt, which improves its ability to withstand the permanent deformation and increased the indirect tensile strength which leads to improving the aging resistance. Such improvements will increase the durability and the cycle life of the asphalt pavements, which will reduce the cost of maintenance and repairs, and also make the asphalt cement easy to work with in hot areas, since the viscosity has increased (Yang and Tighe, 2013). On the other hand, there are possibilities to have some disadvantages of nanomaterial modified pavement under low temperatures. Research conducted by Ghile in 2006 shows that the fatigue resistance of base asphalt cement at low-temperatures is better or higher than modified asphalt cement with nanoclay (Ghile, 2006). Regardless of the disadvantage of modified asphalt with nanomaterials, nanomaterials have many advantages such as decreasing the permanent deformation and reducing or delaying the effect of aging properties under different conditions. Also, nanomaterials modified asphalt can improve the tensile strength and the reduced moisture susceptibility (Goh et al., 2011). Reducing the moisture susceptibility is very important in cold regions because most of the asphalt paved roads are subjected to snow, which usually leads to damage of the pavements, and with modification of pavement by nanomaterials resulting in pavement less susceptible to moisture, a massive amount of energy and money would be saved from less maintenance.
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Characteristic and performance evaluation of nanoparticles modified asphalt mixtures
Asphalt mixtures design techniques attempt to balance the composition of aggregate and asphalt cement to achieve long-lasting performance in a roadway structure. It is identified that asphalt mixtures consist primarily of asphalt cement, mineral aggregates, and air. The primary purpose of mix design is to produce mixtures with high resistance to deformation and cracking. The properties of the produced mixtures depend on the physical and chemical properties of the used materials. Each of the component materials needs to be carefully selected and controlled to ensure that they are of suitable quality for the asphalt mixtures and the expected performance. The aggregate plays a significant role in mix designs or to produce asphalt mixtures. The aggregate should have proper particle size and grading, durable and tough, and consists of angular, the surface of the aggregate is clean and rough (AsphaltInstitute, 2007). However, selecting an aggregate material for use in asphalt mixtures design is also dependent on the availability and cost of the material as well as the type of road construction.
8.6.1
Influence of nanoparticles on resilient modulus of asphalt mixtures
Resilient modulus is the most critical variable to mechanistic design approaches for asphalt structures. It is the measure of asphalt response regarding dynamic stresses and corresponding strains. The main purpose of the resilient modulus test result analyses was to determine if the addition of nanoparticles brought any significant change in the stiffness properties of modified mixtures. Using of Al2O3 with a concentration of 3%, 5%, and 7% as a modifier of asphalt shows that as the temperature increases, resilient modulus decreases regardless of the modifier type and content. The base asphalt cement has the lowest resilient modulus with 3528 mPa among the mixtures, while 5% Al2O3 have the highest resilient modulus 5082 mPa compared with other modified asphalt mixture samples as shown in Fig. 8.7. The improvement in resilient modulus at 25 C for 5% Al2O3 is nearly 44%. The resilient modulus at 25 C showed an average reduction of 71%, 75%, and 73% for 3, 5, and 7% respectively. This leads to identifying that the resilient modulus value is affected by the modifier content and the temperature. The modified asphalt mixtures consistently exhibited higher resilient modulus values than the base asphalt mix. The increase in modifier content produces an enhancement in the elastic properties of the asphalt mixtures. Therefore, modified asphalt has improved the resilient modulus of asphalt mixtures compared to the base asphalt. This might be due to the higher viscosity which gives the mixes polymer properties that lead to better resilience properties. These results indicate that using modified asphalt cement produces asphalt mixtures with higher stiffness and thus higher load-bearing capacity. Moreover, modification of the asphalt mixture using nanosilica shows significant improvement, the additional increment of nanosilica in asphalt blends results in a
Performance of asphalt mixture with nanoparticles
Resilient modulus (mPa)
6000
5082
5000 4000
179
4230
4100 3528
3000 2000 1000 0 0% Al2O3
3% Al2O3
5% Al2O3
7% Al2O3
Modifier content (%)
Figure 8.7 Resilient modulus of the base and Al2O3 nanoparticles modified asphalt mixtures.
positive influence on the resilient modulus of the asphalt mixture (Enieb and Diab, 2017). The value of the resilient modulus has increased by increasing the content of the nanoparticles as shown in Fig. 8.8, which is consistent with previous research. Regardless of the type of binder and the test temperature Al2O3 shows better performance of asphalt mixture compared to nanosilica. It is noteworthy that the form of asphalt mixture was 60/70 penetration grade for both studies, but from different sources, while the test temperature varies, 20 C for Al2O3 and 25 C for nanosilica. Also, increase in resilient modulus of the modified mixtures led to expect mixtures with high elasticity and therefore better resistance to rutting than the base mixture. The results of resilient modulus of modified asphalt mixture using the same concentration of nanosilica 0%, 2%, and 4%, conducted at a temperature of 25 C, show higher improvement as the base asphalt cement was PG-76. The results of the resilient modulus tests are shown in Fig. 8.9. It is observed that the modified asphalt mixtures with 4% nanosilica have the lowest susceptibility to fatigue deformation with the 720
Resilient modulus (mPa)
720
690
700 680 660 625
640 620
600
600 580 560 540 0% NS
2% NS 4% NS Modifier content (%)
6% NS
Figure 8.8 Resilient modulus of nanosilica modified asphalt mixtures.
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Resilient modulus (mPa)
2500
2037
2000 1500
1624 1170
1000 500 0 0% NS
2% NS Modifier content (%)
4% NS
Figure 8.9 Resilient modulus of nanosilica modified asphalt mixtures.
highest resilient modulus of 2037 mPa, while the base sample as expected has the highest susceptibility to fatigue deformation with a low resilient modulus of 1170 mPa. It indicates that the addition of nanosilica is able to improve resistance to fatigue deformation at intermediate temperatures compared to the control sample (Yusoff et al., 2014). The modification of asphalt mixtures with nanoparticles has a significant influence on the resilient modulus of asphalt mixtures and is able to improve the resistance to fatigue to mitigate the pavement distress.
8.6.2
Effect of nanoparticles on dynamic creep
The load when applying to the surface of asphalt mixtures deforms although a majority of deformation will be recovered after the pressure is removed. This phenomenon is referred to the characteristics of asphalt which is identified as a visco-elastic material. However, a minute quantity of irrecoverable viscous deformation would remain in mixtures. With applying lots of load cycles, the slight amounts of deformation would be accumulated and eventually result in rutting in the surface of asphalt mixtures. Figs. 8.10 shows the results of dynamic creep modulus for unaged samples of base asphalt mixtures and Al2O3 nanoparticles modified asphalt mixtures at a temperature of 40 C and a load of 80 kPa. The results show that with increasing the modifier concentration, the stiffness increased up to 5% Al2O3. The 5% of both modifiers show the higher amount of resistance to rutting (high stiffness). Meanwhile, the base asphalt mixtures as expected recorded the lowest resistance to the deformation (low stiffness). Moreover, the 7% Al2O3 shows a decrease in the stiffness due to the agglomeration among the nanoparticles with increasing the percentage of nanoparticles in asphalt matrix (Ali et al., 2017). The results are in good agreement with previous studies conducted by Yusoff et al (Yusoff et al., 2014) and Chelovian and Shafabakhsh (Chelovian and Shafabakhsh, 2017). They investigated the influences of nanosilica on modified asphalt mixtures and found that the rutting depths of nanomaterials modified asphalt mixtures decreased compared to the base asphalt mixtures, and a reduction in rutting depth was noted for a higher percentage of nanomaterials in the asphalt mixtures.
Dynamic creep modulus (MPa)
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181
300 270
256
250 200
185 164
150 100 50 0
Base asphalt mixes
3% Al2O3
5% Al2O3
7% Al2O3
Modifier content (%)
Figure 8.10 Dynamic creep modulus of modified asphalt mixtures with Al2O3.
8.6.3
Impact of nanoparticles on the rutting distress
Rutting depth (defromation in mm)
The rutting of asphalt mixtures has an essential effect on the performance of the asphalt for the period of lifetimes. Rutting not only decreases the useful service life of the pavement but also it might distress basic vehicle handling, which can be dangerous to road operators. The depth and rate of rutting depend on load and volume of truck traffic, tire pressure, temperature, construction practices, the thickness of asphalt, asphalt cement type, aggregate, and mixture properties. Besides, the primary contributing factors are traffic and high temperatures. Fig. 8.11 shows the results obtained during the wheel-tracking tests carried out for unaged samples of modified asphalt mixtures with Al2O3 nanoparticles. The combination of the asphalt cement with the modifier results in an enhancement in the resistance against deformations. The addition of the Al2O3 nanoparticles modified asphalt mixtures showed a reduction in the rutting in high temperatures (50 C). Besides, it can be noted clearly that the 5% concentration has better performance of rutting resistance and base asphalt mixtures show the lowest value in resistance to rutting; the use of 2.5
2.35 2
2
1.7 1.4
1.5 1 0.5 0
Base asphalt
3% Al2O3
5% Al2O3
7% Al2O3
Modifier content (%)
Figure 8.11 Rut depth of Al2O3 nanoparticles modified asphalt mixtures.
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Al2O3 nanoparticles to modify base asphalt cement to produce asphalt mixtures is considerably more efficient than the use of base asphalt. This result is similar with the findings of other studies when using SBS and crumb rubber to modify asphalt mixtures as the increase of both modifiers leads to improvement in asphalt properties (Moreno-Navarro et al., 2014). Also, it is similar with a study conducted by Polacco et al. when they used sodium montmorillonite (Na-MMT) and organophilic montmorillonite (OMMT) nanoclay to modify asphalt mixtures. The results show that the modifications have promising potential to decrease the permanent deformation asphalt pavements (Polacco et al., 2008).
8.6.4
Influence of nanoparticles on moisture susceptibility
The breaking of the bond between asphalt and aggregate is identified as stripping, and the phenomenon that causes stripping between asphalt cement and aggregate mixtures is very complicated and not yet understood entirely (Xiao et al., 2010). The stripping will slowly decline the strength of the materials throughout the years which will be apparent as cracking, rutting, corrugation, traveling, shoving, etc. The procedure of performing to evaluate moisture susceptibility was based on AASHTO T283. This test is not a performance test, but it serves two purposes. First, it identifies whether a combination of asphalt cement and aggregate is moisture susceptible. Secondly, it measures the effectiveness of antistripping additives (Asphalt-Institute, 2007). Figs. 8.12 indicates that all asphalt mixtures regardless of modification have TSR values more than 80% criteria value according to AASHTO T283. A TSR of base asphalt mixtures is 85%. The addition of nanoparticles makes a significant improvement in the adhesion between the asphalt cement and aggregate. Merely the modifier gets into the spaces
99 100
97 93
TRS (%)
95 90 85 85 80 75
0% Al2O3
3% Al2O3
5% Al2O3
7% Al2O3
Modifier content (%)
Figure 8.12 Moisture susceptibility of Al2O3 nanoparticles modified asphalt mixtures.
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183
between the aggregates, better coating the aggregates. Therefore, more resistance to moisture damage is provided. The TSR results show that the addition of nanoparticles leads to increase in the resistance to moisture susceptibility up to 5%. The 7% Al2O3 shows an improvement of 9%. Using nanosilica to modify asphalt mixtures shows similar results to that of Al2O3 nanoparticles which leads to reduce the susceptibility of asphalt mixtures to moisture damage; it was found that modified asphalt mixture samples achieved a higher TSR value compared with base asphalt mixtures.
8.7
Durability of modified asphalt mixtures
Aging of asphalt concrete affects the stiffness of the asphalt cement and may result in excessive stiffness. To be able to characterize asphalt concrete adequately requires that samples to be evaluated should be aged to simulate in-place properties of HMA (Hot Mix Asphalt) mixture. Aging in the field is significantly affected by the initial voids in the mix, the densification of the mixture under traffic, and the amount of heat applied to the mixture during production. Because of the rate of aging of asphalt cement in the mixture is affected by the mixture properties, such as in-place air voids, the entire mixture should be aged. The Superpave mix design requires that the mixture be at compaction temperature for 2 h after mixing and before compaction. This process simulates some initial aging, but primarily it allows for absorption of some of the asphalt cement into the aggregate. Superpave also developed a method to age the compacted mixture to simulate in-service aging in the field. This process involves placing the compacted samples in an oven for an extended period to allow for oxidation of asphalt cement. Aging is primarily associated with the loss of volatile components and oxidation of the asphalt during asphalt concrete construction which is known as short-term aging and progressive oxidation during service life in the field recognized as long-term aging. Asphalt, when it contacts with air (oxygen), oxidizes well gradually, increasing its viscosity resulting in harder asphalt with less flexibility. The value of viscosity is extremely dependent on the temperature, time, and the asphalt film thickness.
8.8
Challenges of nanoparticles modification
Asphalt pavement is one of the materials commonly used for roads and airports construction. The scientists and engineers are continually trying to enhance its performance. The surfaces of roads are subjected to numerous loadings of heavy axes and severe weather conditions, so the surfaces must have sufficient strength against cracking, fatigue, and creep resistance. The main purposes of characterization and modification of the physical, chemical, morphological, rheological, and mechanical properties of asphalt pavement are to overcome or mitigate its distress. It was found that the modification of asphalt cement using nanomaterials leads to improvement in the viscoelastic behavior of the asphalt and changes its rheological
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properties. Also, the act of nanomaterials inside the asphalt matrix is not fully understood, and more studies should be carried out to investigate the chemical properties which are the most important properties in the field of nanomaterials modified asphalt cement. One of the greatest challenges that face the researchers is identifying the proper way and time to mix nanomaterials with base asphalt mixtures. Also, the speed of mixing plays a big role in the uniform dispersion of nanomaterials, the uniform dispersion of the modifiers inside the blends results in a good estimation of the behavior of asphalt mixtures. Moreover, some researchers use an ultrasonic machine or chemical solvate to ensure that the nanoparticles will not be agglomerated during the mixing process.
8.9
Conclusion
The main objectives of this research were to characterize the mechanical properties of modified asphalt mixtures. The addition of a modifier to the base asphalt mixture is able to improve the viscoelastic behavior of the asphalt and change its rheological properties. One of the types of modifiers used is nanoaluminum oxide (Al2O3), which has a different amount of influence, decreasing or increasing, on the mechanical properties of the asphalt mixture. After conducting laboratory tests on asphalt mixtures with different nanoparticles content and after analyzing the data and comparing the results, the following conclusions are drawn: 1. It was found that the modified asphalt mixtures by Al2O3 consistently exhibited higher resilient modulus values than the base asphalt mixtures and the 5% concentration for both modifiers has the highest value. The increase in modifier content produces an enhancement in the elastic properties of the asphalt mixtures. Therefore, modified asphalt has improved the resilient modulus of asphalt mixtures compared to the base asphalt. 2. Evaluation of dynamic creep among the base asphalt mixtures and modified asphalt mixtures shows that the modifier has a significant influence to improve the resistance to permanent deformation of base asphalt mixture and 5% concentration of the modifier has the lowest permanent deformation while the base mixture has the highest deformation among the mixes. 3. The modified mixtures have good resistance to rutting compared with the base asphalt mixture which has the lowest resistance to rutting. Also, 5% of modifier shows the highest performance of asphalt mixture among the mixtures. 4. The TSR results indicate that the modified samples have slightest susceptibility to moisture damage than modified samples with Al2O3 nanoparticles, meanwhile the base asphalt cement is more susceptible to moisture damage. Moreover, the 7% concentration shows the highest improvement, which might be due to that the behavior of Al2O3 is acting differently with the presence of water or due to some chemical reactions.
Acknowledgments The Ministry of Science has supported part of this work, Technology and Innovation (MOSTI), Malaysia for research funding through project 03-01-02-SF0999.
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