Nanotechnology for Asphalt Binders Mohamed Elshaer, Graduate Student, Faculty of Engineering, Cairo University, Giza, Egypt Phone: 20-100-384-5599, E-mail:
[email protected]
1. Background and Introduction 1.1. TRB Webinar ―TRB will conduct a webinar that will explore the use of nanomaterials in asphalt binders used for paving applications. The use of nanomaterials in pavement construction, particularly asphalt binders has the potential to lead to enhanced mechanical properties. Preliminary research demonstrates that asphalt modified with nanomaterials may provide enhanced strength and durability. Panelists will discuss different types of nanomaterials, their use in emulsified asphalt, and how they may contribute to improved asphalt performance‖ [1]. Webinar objectives: ―At this webinar, attendees will be able to understand: General concepts about nanomaterials, such as clays and their use in emulsified asphalt, and how they contribute to increase strength and durability of paving asphalts Why nanomaterials may lead to more durable and long-lasting pavements The various types of materials and how to select potential nano modifiers for asphalt‖ [1]. 1.2.Asphalt materials ―In the United States, transportation infrastructure investments account for 770 of the Gross Domestic Product (GDP) according to the National Asphalt Pavement Association. Over 550 million tons of hot-mix asphalt (HMA) is produced annually for construction projects. Increasing traffic loads and traffic volume, combined with the rising cost of asphalt, have led to an urgent need to improve the durability, safety and efficiency of asphalt pavements through asphalt modification. Asphalt mixtures are composed of very irregular aggregates bound together with hydrocarbon based asphalt, with a low volume fraction of voids dispersed within the matrix. Polymer modified asphalts have increasingly been used over the last decade to minimize lowtemperature cracking and high-temperature rutting while improving the fatigue cracking resistance of asphalt concrete. Polymer modifiers fall into one of two major categories: (1) elastomeric (rubber/polymer) modifiers including styrene/ butadiene polymers, natural rubber, and crumb rubbers (both virgin and recycled) and (2) blastomeric modifiers such as polypropylene and polyethylene‖ [2]. 1.3.Nanotechnology and the current development in pavement materials ―Nanotechnology is the creation of new materials, devices, and systems at the molecular level as phenomena associated with atomic and molecular interactions strongly influence macroscopic material properties. Even though engineers are interested in material properties
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at the macro and meso scales, the nano and micro scales provide fundamental insight for the development of science and technology. Although improvements in asphalt performance have been achieved through polymer modification, it will be interesting to explore what nanotechnology offers in improving asphalt pavement performance. In August 2006, the NSF Workshop on Nano modification of Cementitious Materials was held to develop a "Roadmap for Research" for Portland cement concrete and asphalt concrete using nanotechnology. Part 1 states that nano-science and nanotechnology may lead to progress in asphalt pavement technology. Researchers are planning to form an ad hoc consortium to study and develop tools to model asphalt's physio-chemical properties that effectively establishes the field of "asphalt nano-material science. Greenfield has studied the molecular simulation of asphalt-like materials. Birgisson envisions that nano studies are needed to develop safe and sustainable pavement infrastructure, stating that the future life of pavements could reach two to three times their current life. Other researchers have also initiated investigations into the use of nanotechnology in Portland cement concrete. Ideal asphalt should possess: high relative stiffness at high service temperatures (summer) to reduce rutting and shoving‖ [2]. 2. Different nanomaterials to control asphalt binder 2.1. Nano-modified asphalt materials ―In the experimental testing montmorillonite, nanoclay at 2% and 4% by weight of asphalt was blended in asphalt binder at a high temperature to exfoliate the nanoclay within the asphalt. The asphalt binder was then characterized using the Superpave™ rotational viscosity, dynamic shear modulus, and direct tension test. The rotational viscosity results indicate that the addition of the two types of nanoclay, Nanoclay A and Nanoclay B, increased the rotational viscosity by an average of 41% and 112%, respectively, across test temperatures 80, 100, 130, 135, 150 and 175o C. It was found that the dynamic shear complex modulus (G*) value increases significantly across a range of testing temperatures (from 13 to 70oC) and loading frequencies (0.01–25 Hz). With 2% Nanoclay A reinforcement in the asphalt binder, the complex shear moduli generally increased by 66% while the 4% Nanoclay A reinforcement in the asphalt binder generally increased the shear complex moduli by 125%. The 2% and 4% Nanoclay B increased the shear complex moduli by 184% and 196%, respectively. In terms of direct tension strength, the use of Nanoclay A and Nanoclay B reduced the strain failure rate of the original binder while the secant or direct tension moduli showed increase with the addition of the nanoclays. In furtherance of this research, nanoclaymodified asphalt is being tested at percentages higher than 4% to underscore the fact that nanoclays may have the potential to reduce rutting and cracking‖ [2]. 2.2. Non-Modified and Polymer-Modified Nanoclay ―The study investigated the rheological properties of asphalt binders modified with nanomaterial additives. The additives used are non-modified nanoclay (NMN) and polymer modified nanoclay (PMN). They were added to the control PG 58-34 asphalt binder at concentrations of 2% and 4% by the weight of the asphalt binder, respectively. Superpave TM binder tests were employed to evaluate the characteristics of the nano-modifed binders. Rheological properties of nano-modifed asphalt were analyzed by use of asphalt binder tests such as Rotational Viscosity (RV), Dynamic Shear Rheometer (DSR) and Bending Beam Rhometer (BBR). In addition, the short- and long-term aging properties of nano-modified asphalt were analyzed, with the aging process simulated by Rolling Thin Film Oven (RTFO) and the Pressure Aging Vessel (PAV). The dissipated work per load cycle of all asphalt Mohamed Elshaer
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binders was examined, in order to better understand the properties of nano-modified asphalt. The results reveal that both viscosity and complex shear modulus of asphalt binder remarkably increase when the NMN is added into the control asphalt, and decrease slightly when the PMN is added. In addition, from the dissipated work perspective, the rutting performance of NMN modified asphalt binder is improved and fatigue cracking resistance of PMN modified asphalt binder is enhanced compared to the control asphalt binder‖ [3]. ―NMN and PMN microstructure images are observed by Hitachi S-4700 field emission scanning electron microscope (FE-SEM) (Figure 1 and Figure 2). Microstructure images of 4% NMN and PMN modified asphalt binder were obtained by using a Hitachi SU6600 FESEM with a cryogenic stage and shown in Figure 1 and Figure 2. The SU6600 images showed that the NMN was mainly found in conglomerates, which ranged in size from 50 to 15 microns. The dispersion of the PMN was slightly better with an average conglomerate size of 4 microns, but there were a few extremely large conglomerates (~80 microns). From the figures, it can be seen that agglomeration phenomena of nanomaterials also occurred in the asphalt binder and nanomaterials were melted uniformly in the control asphalt binder‖ [3].
Figure 1. FE-SEM microstructure images of non-modified nanoclay and NMN modified asphalt binder
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Figure 2. FE-SEM microstructure images of polymer-modified nanoclay and PMN modified asphalt binder ―Based on the tests results of nanomaterials modified asphalt, the following conclusions can be made. 1) The addition of NMN into the control asphalt binder increases the viscosity of the asphalt binder; however, the viscosity of PMN modified asphalt binder slightly decreases relative to the control asphalt binder. In addition, all asphalt viscosity data at 135oC pass the specification of SuperpaveTM Standard and it means the construction paving temperature does not influenced. 2) The NMN modified asphalt binder has higher complex shear modulus than the control asphalt binder and the PMN modified asphalt binder has lower complex shear modulus than the control asphalt binder before or after the RTFO and PAV aging process. From the dissipated work standpoints, the addition of NMN in the control asphalt binder can improve the high temperature properties of unaged, RTFO-aged and PAV-aged asphalt binders. The addition of PMN in the control asphalt binder does not significantly enhance the high temperature properties of unaged, RTFO-aged and PAV-aged asphalt binders. In addition, with the addition of PMN in the control asphalt binder increases the recovery ability of asphalt binder while the addition NMN in the control asphalt binder decreases the recovery ability of asphalt binder. 3) BBR test results show that the stiffness of NMN and PMN modified asphalt binders approach to that of control asphalt binder. From the SuperpaveTM grade perspective, the stress relaxation and low temperature performance of NMN and PMN modified asphalt binders is the same as the control asphalt. In summary, the addition of non-modified nanoclay (NMN) in the control asphalt binder enhances the performance of the asphalt binder. Furthermore, the research team plans to conduct the performance tests of asphalt mixture. The ongoing research focuses on the microstructure performance and simulation model of asphalt binder and asphalt mixture‖ [3].
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2.3. Asphalt Mixtures Modified with Nanosilica ―In this study, the nanosilica was added to the control asphalt at contents of 4% and 6% based on the weight of asphalt binders. Superpave™ binder and mixture tests were utilized in this study to estimate the characteristics of the nano-modifed asphalt binder and mixture. The Rotational Viscosity (RV), Dynamic Shear Rheometer (DSR), Bending Beam Rhometer (BBR), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Asphalt Pavement Analyzer (APA), Dynamic Modulus (DM) and flow number (FN) tests were used to analyze rheological properties and chemical bonding changes of the nanomodified asphalt binder and the performance of the nano-modified asphalt mixture. In addition, the performance of nano-modified asphalt after Rolling Thin Film Oven (RTFO) short-term and Pressure Aging Vessel (PAV) long-term aging was assessed as well. The dissipated work per load cycle for the asphalt binder was used to evaluate the rheological properties of the nano-modified asphalt binder. Based on the binder test results, it was found that the additional nanosilica in the control asphalt binder slightly decreased the viscosity of the control asphalt binder, maintained low dissipated work per load cycle, held the similar low-temperature performance to the control asphalt, and had a positive effect on antioxidation. From the mixture test results, the dynamic modulus and flow number of nanomodified asphalt mixtures improved, and the rutting susceptibility of nano-modified asphalt mixtures was reduced compared to the control asphalt mixture. In general, the findings from this study show that the anti-aging property and rutting and fatigue cracking performance of nanosilica modified asphalt binders are enhanced and the addition of nanosilica in the control asphalt mixture significantly improves the dynamic modulus, flow number and rutting resistance of asphalt mixtures‖ [4]. 2.4. Nanoclay and Carbon Microfiber ―The objectives of this research are to modify an asphalt mixture with two materials— nanoclay and carbon microfiber—and to investigate the interactions of chloride deicer solutions with nano- and/or micromodified and unmodified asphalt mixtures in terms of indirect tensile strength (ITS) and fracture energy. Artificial neural networks (ANNs) were used in this study to establish predictive models and quantify the complex cause-and-effect relationships between the nano- or micromodification and conditioning of asphalt mixtures and the resulting mechanical properties. Four influential variables (nanoclay content, microfiber content, deicer type, and deicer dilution ratio) were collectively examined to predict the ITS and fracture energy of asphalt mixtures, and a back-propagation neural network of three layers with seven or nine hidden nodes was employed respectively. The established ANN models were then successfully used for numerical investigations on the parameters affecting the asphalt properties. The addition of polysiloxane-modified montmorillonite and/or carbon microfiber (both at less than 2% by weight of asphalt binder) can enhance the tensile strength fracture energy of asphalt concrete mixtures and reduce their moisture susceptibility and cracking risk, and such benefits are especially significant when the asphalt concrete is conditioned in water or chloride-based deicer solutions. This evaluation makes it possible to design asphalt mixtures for a desired level of ITS or fracture energy in the absence or presence of common chloride-based deicer solutions there are few studies on the use of carbon microfiber to reinforce asphalt pavement. Currently there is also the need to explore the combined use of and potential synergism between micro- and nanosized modifiers in improving the properties of asphalt materials, especially when they are exposed to deicer solutions‖ [5]. ―The interactions of chloride deicer solutions in terms of indirect tensile strength and fracture energy were examined as well. Artificial neural networks (ANNs) were chosen as a tool to Mohamed Elshaer
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establish predictive models and quantify the complex cause-and-effect relationships between the nano- or micro- modification and conditioning of asphalt mixtures and the resulting mechanical properties. The following conclusions can be drawn from this study: 1. The ANN models were established by appropriately choosing the architecture and training process. Four influential variables (nanoclay content, microfiber content, deicer type, and deicer dilution ratio) were collectively examined to predict the ITS and fracture energy of asphalt mixtures, and a back propagation neural network of three layers with seven or nine hidden nodes was employed, respectively. 2. From a modeling perspective, ANNs were used to achieve better understanding of the complex cause-and-effect relationships inherent in the deicer/HMA systems and were successful in finding some meaningful, logical results from the experimental data associated with the indirect tensile strength testing. 3. The addition of polysiloxane-modified montmorillonite and/or carbon microfiber (both at less than 2% by weight of asphalt binder) can enhance the tensile strength fracture energy of asphalt concrete mixtures and reduce their moisture susceptibility and cracking risk, and such benefits are especially significant when the asphalt concrete is conditioned in water or chloride-based deicer solutions. The practical implications of such modifications are substantial. For instance, in cold regions in which the use of chloride deicers may aggravate the moisture damage of asphalt concrete, a high-grade binder or polymer-modified binder may no longer be needed if one can modify a low-grade binder at low cost using these inexpensive nano- and microsized materials. 4. The optimal mix design, in terms of high tensile strength and high fracture energy, was affected by the concentration of deicing solution and amount of nanoclay and carbon microfiber added. In general, the optimal asphalt mixtures featured only a certain amount of microfiber or an appropriate combination of nanoclay and microfiber. 5. This evaluation makes it possible to design asphalt mixtures for a desired level of ITS or fracture energy in the absence or presence of common chloride-based deicer solutions‖ [5].
Reference 1. A. James, Z. You, R. Mohan. ―TRB Webinar: Overview of Nanotechnology and Use of Nanomaterials as Modifiers for Asphalt Binders”. 2. Z. You, J. Mills-Beale, M. Foley, S. Roy, Gr.M. Odegard, Q. Dai, S.Goh(2011).‖Nanoclay-Modified Asphalt Materials: Preparation and Characterization‖. www.highbeam.com/doc/1G1-251856692.html 3. H. Yao, You Z., L. Li, X. Shi, S. Goh, J. Mills-Beale, D. Wingard. ―PERFORMANCE OF ASPHALT BINDER BLENDED WITH NON-MODIFIED AND POLYMER-MODIFIED NANOCLAY”. 4. Yao, H., You, Z., Li, L., Lee, C., Wingard, D., Yap, Y., Shi, X., and Goh, S. ―Properties and Chemical Bonding of Asphalt and Asphalt Mixtures Modified with Nanosilica‖ J. Mater. Civ. Eng. ascelibrary.org/doi/abs/10.1061/(ASCE)MT.19435533.0000690 5. X. Shi.; S. Goh; M. Akin; S. Stevens; and Z. You‖ Exploring the Interactions of Chloride Deicer Solutions with Nanomodified and Micromodified Asphalt Mixtures Using Artificial Neural Networks” JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / JULY 2012 / 811. pp 813 Mohamed Elshaer
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