PRELIMINARY REPORT:
A Review on The Exploration of Nanomaterials Application in Pavement Constructions
Introduction:
Nanotechnology is one of the main area of interests of studies among experts, engineers, medicals and physicists. It is about making understandings of the building blocks of materials and to have control over the properties of different materials. Nanotechnology is having a prominent effect on our lives in every field. Since 1990s, development on tremendous scale in the implementation areas of nanotechnology such as science and education, materials and construction, manufacturing, Nano electronics and computer information technology, medicine and healthcare, aeronautics and space exploration, environment and energy, biotechnology and agriculture, and national security [1–5]. Their applications have a promising impact on our lives and therefore need a perfect understanding of them complexities and their characteristics. Furthermore, both academy and industry are interested in this field of studies, therefore have a diverse scope.
In our scope of studies, to improve the performance of pavements using asphalt mixtures, various modifiers in forms of nanoparticles are being used in the field to enhance the quality characteristics of the binder. Different types of modifiers applicable for specific uses are available in market and standards and specifications are generated. Many researchers have found that polymeric nanocomposites are effective in modification of virgin asphalt binder with well-proportioned mixture of nanomaterials; it has improved engineering properties of the binders to the greater extent. The literature review of the last decade researches on applications and usage of nanomaterials can help us in understandings and something beneficial seems promising. The theory and historical development including the method used among researchers in evaluation the structural and morphological characteristics of modified binder with nanoparticles. In the application of flexible pavements using Nano clays, Nano-hydrated lime and nanoparticles of carbon in binders for modifications of engineering properties are the research focus. Some studies have found that nanomaterials are the cause of decreasing the penetration in binder and its ductility and increase in its softening point value.
Alongside, some rheological properties that is performance grade, rutting resistance, low-temperature cracking resistance and aging resistance also showed better improvements [12]. Additionally, engineering properties of proportioned mixtures of binder with different nanomaterials, incorporating asphalt mixtures, were significantly improved particularly in the areas of stiffness, rutting resistance, indirect tensile strength and resilient modulus. Also, the effect of different types of nanoparticles, suitable dosages, modifying procedures, problems and benefits on asphalt binder and mixture were explained [5]. It is expected that in future the implementations of nanotechnology would have major impacts for better pavement performance.
Objectives of the study can be summarized as follows:
i- To evaluate certain characteristics of binder mixtures modified with nanoparticles, that is their structural and morphological characteristics.
ii- To Study the effects of different types of modifiers, suitable proportions and different problems.
iii- To determine the modifying procedures.
iv- To investigate the impact of nanoparticles in binder for better performances of pavements.
Literature Review:
Defining Nanotechnology:
It is the scientific and engineering design, synthetic, characterization and application of micro materials and devices, that is on nanometer scale i.e. one billionth of a meter [1]. Generally, nanomaterials have rod like or globular or more complex structure. Clusters are the particles having size of less than 10 nm and these particles are near spherical in nature. The number of atoms in a cluster vary in increasing order with the size of a cluster. A size of 1 nm in cluster there are around 13 atoms accommodated while in a cluster of size 100 nm diameter, there are 107 atoms are accommodated. Clusters may also exist in symmetrical shapes and some are amorphous in nature.
In normal practices that are being adopted in highways constructions and research works, addition of modifiers is either being done by adopting wet method or dry method for improvements in engineering properties in highways construction. However, there has been a recent trend among pavement engineers and researchers to explore the properties of binders using Nano scale materials. Figure (1) shows that how nanomaterials from large scale to quantum level has been evolved and better understood with time for the enhancements of properties. Nanomaterials have high surface area to volume ratio which provide high chemical reactivity.
Figure (2) below illustrates the specific surface area and particle sizes related to concrete materials. Furthermore, nanotechnology is a key technology which allows us to understand the characteristics of materials on nan scale and is a sustainable material for construction and in many other products.
Development of Nanomaterials:
This term is first used by the Japanese Engineer who described the parts which were manufactured with the precision in the range of 0.1 nm to 100 nm. This terminology has implied new meaning and separate field was emerged in Nano sciences and its applications. Later in early 1980s, a new approach is adopted by Drexler which is more diverse in scope in today’s research and development. He corresponded to the atom-by-atom manipulative, hard tech processing methodology [12].
Our growing interest in the field is mainly because of the reason that our understandings are refined and advanced in the course of time. We could manipulate structural arrangements on quantum level, in order to achieve the user friendly characteristics of the materials. Our knowledge with the advancements of numerical algorithms and numerical methods is getting us to the refined understandings about the materials. These researches state that with studying the materials on nanoscales, there are more features that need our focused for keen understandings.
Nanomaterials and their Structural Characterization:
The primary problem that researchers face in the field of nanotechnology is the understandings of instrumentations which are used in studying of the materials on micro scale. Observations, measurements, and manipulating individual particles in nanostructures of nanomaterials is a great challenge in the face of our lack of understandings in pavement engineering. To characterize nanomaterials and nanostructures, surface analysis technique and conventional characterizing method for materials in bulk. Among different methods X-Rays Diffraction (XRD), Electron Microscopy (EM) which includes scanning electron microscopy (SEM) and Field Emission Scanning Electron Microscopy (FE-SEM) [7, 8].
Analysis using X-Ray Diffraction (XRD) Technique:
X-Rays Diffraction Technique has applications in addressing issues related to the identification of crystal structures of solids, in addition to their geometries, crystal lattice constants, identifying unknown materials and bonds characteristics, orientations of crystal structures and poly crystals, defects, residual stresses and strains, etc. In this method a collimated beam of X-Rays, of wavelength in the range of 0.7 A to 2.0 A, is directed to incident on a sample and the ray of radiation is diffracted by the crystalline phases of the specimen. These diffracted lights are illustrated on screen and is characterized in patterns to portray the crystal structures [12].
This XRD method is a NDT (Non Destructive Testing) Method and is helpful in investigating the following properties accurately:
(i) Crystal Structure
(ii) Polymorphism (phase identification of crystal lattice)
(iii) Identifying fillers, pigments and additives
(iv) To identify active and chemically reactive compounds and excipients
(v) To manipulate the orientation and texture of materials.
(vi) To locate the region of residual stress and strain
X-Rays Diffraction Technique is applied to the materials which are only fine grained and in powdered forms or to manufactured parts, films, plaques, fibers, cured components, coatings, wafers or multilayer systems.
Scanning Electron Microscope (SEM) Method:
This method brings in use electron microscope which illustrate the specimen’s surface topography and its composition and properties by projecting the beam of electrons on the sample. It also includes secondary electron image, back-scattered images and X-Ray maps. Furthermore, in addition to the topographical information is produced, this technique is facilitating the information about chemical composition near the surface.
Field Emission Scanning Electron Microscopy (FE-SEM):
This technique is more advanced than that of Scanning Electron Method to illustrate the images of surface texture and morphological characteristics of any kind of materials. The specimen should be well prepared before scanning, therefore should meet the requirements to be tested. The primary benefit of applying this method is because of its high resolution and long working length between magnetic lens and sample from conventional methods.
The signal which is received portrays on signal and display information of surface texture and topography, their composition and other physical properties.
It gives the following information including: [12]
(i) Thickness measurement of thin coatings and films
(ii) Correlation of surface appearance and surface morphology
(iii) Characterization of size, size distribution, shape and dispersion of additives, particulates and fibers in
composites and blends.
(iv) Measurement of height and lateral dimensions of nanometer-sized objects
(v) Characterization of cell size and size distribution in foam materials
(vi) Elemental analysis of micron-sized features
(vii) Fracture and failure analysis
(viii) Defect analysis
Development and Research on Nanomaterials and their Applications in Pavements:
Currently, to improve the performance of pavements using asphalt mixtures, various modifiers in forms of nanoparticles are being used in the field to enhance the quality characteristics of the binder. Different types of modifiers applicable for specific uses are available in market and standards and specifications are generated. Many researchers have found that polymeric nanocomposites are effective in modification of virgin asphalt binder with well-proportioned mixture of nanomaterials; it has improved engineering properties of the binders to the greater extent. The theory and historical development including the method used among researchers in evaluation the structural and morphological characteristics of modified binder with nanoparticles. In the application of flexible pavements using Nano clays, Nano-hydrated lime and nanoparticles of carbon in binders for modifications of engineering properties are the research focus. Some studies have found that nanomaterials are the cause of decreasing the penetration in binder and its ductility and increase in its softening point value.
Nano clay:
It is naturally occurring mineral and is naturally subjected to variations in their constitution. The impurities may affect their properties. Most often clay consists of alumina–silicates, layered in structure, and is bonded silica tetrahedron, SiO4, with alumina octahedron, AlO6, in various ways. montmorillonite (MMT) is prevalent silicate with thickness of their layers of 1 nm and is large and active surface area which frequently interact with asphalt and depends upon what type of material it is mixed with. This material is environmental friendly and is readily available and enough research is done on exploring it. In Figure 3, surface treatment process of the Nano clay materials is being shown.
In the figure (4), it is shown that the organic constituent is embedded among the clay layers to expand the layers without disturbing the spatial relationships of different layers. Moreover, to improve the compatibility of clays with polymers and to enhance bond of Nano clay, polymers are added to the Nano clay.
Research is underway on compatibility of Nano clay to modify asphalt binders because it contains highly pure and compatible MMT particles. Different percentages of Nano clay, that is range from 3 % to 5 %, by weight of asphalt binder are used by researchers.
The Scanning Electron Microscopy (SEM) image of montmorillonite MMT is shown in figure 5.
Chinese Researchers [42] are using montmorillonite MMT and organo-modified montmorillonite (OMMT) as modifiers in binders. With the increase in softening point and viscosity of the modified binders, at high temperature, these modifiers have shown complex behaviors. Viscoelastic properties have shown considerable enhancement after added modifiers in binders. This property is helpful mainly in improving rutting resistance at high temperature. Another researcher, Yu et al. [36], have carried out investigations on the effects of OMMT on thermo-oxidative and UV aging properties of asphalt.
Besides this, numerous researches are being done in the American universities, on the effectiveness of the modifying Nano clay in pavement binders. You et al. [9] conducted a research study on Nano material effectiveness, dictates that it can enhance the shear modulus of binder, better low temperature cracking resistance, and viscoelasticity. It is also shown the morphological image of the binder with Nano clay as modifier in figure (6). Rheological results of different researchers have shown the similar trend with previous research findings.
Nano Hydrated Lime:
Hydrated lime is mostly used in construction industry. This material is beneficial in mitigating the moisture related damage and enhance its performance. Figure (7) indicates the sub Nano sized hydrated lime (SNHL), with average size of particles of 660 nm, produced in Los Angeles abrasion machine in material laboratory. This material, in powdered form, was dispersed in acetone and then the suspension is mixed with the lime. The resulting mixture reacts with the aggregates and enhance the strength of the bond between the asphalt and aggregates.
Carbon Nanoparticles:
Nanoparticles of carbon are also used in pavement constructions to modify the binding properties of asphalt as shown in the figure (8). In the applications of nanotechnology, carbon nanoparticles, which are also nanotubes of carbon, made from graphite sheets. These particles vary in thickness, length and numerous layers, which have larger surface area per unit weight.
Titanium Dioxide (TIO2):
Titanium Dioxide is a strong and useful photocatalytic material which is relatively safe, durable, stable and economical and is compatible in nature with binder, that is with traditional construction materials such as cement, binders, and aggregates. It is also effective under normal atmospheric temperature. NiO2 is oxidized into water soluble nitrates and oxidizing SO2 into sulfates.
Number of researchers have been working on TiO2 as nanomaterial modifier in pavements. One of the researches that Chinese has been conducting is the Nano material Titanium Di-Oxide in binders, as additive, is studied for their flexural fatigue performance and resistance in abrasion experimentally. The promising results indicates the enhancement in properties of abrasion resistance in addition to the improvement in compression strength and fatigue performance.
Methodology:
· The literature of the researches for the decade needs to be studied thoroughly in order to get keen insights and thorough understandings of the binder material and different types of nanomaterials that can be used effectively to enhance the properties of the binder material.
· From the data collected from literature review, different proportioning ratios to be developed for different nanomaterials that are to be used to get the desirable properties for the respected pavement constructions.
· From that charts and tables are to be generated, incorporating different kinds of nanomaterial modifiers, by studying different researches.
· Modifying procedures for the usage of different materials could be developed as per the requirements of the usage of different nanomaterials.
· Later on, conclusions of the whole study are to be propounded that is the guidelines for the usage of nanomaterials in construction incorporating environmental climates and socioeconomic conditions of the region.
Data Sources:
Data is primarily taken from past researches and journals. Number of research works have conducted on the application of nanomaterials in pavement constructions. These researches have their main focus on the modifications of binders’ properties in pavements.
Our focus is to conduct a thorough study of all the past researches and derive a detailed data for the general guidelines of different types of nanomaterials to be used as per the requirements of the properties of the pavement constructions and recommend their well proportioning design values7•.
Preliminary Findings:
Nanomaterials are the promising materials in the field of pavement engineering, to enhance the engineering properties of the binders. Researchers has been focusing on the modification of binder in pavement constructions, using different Nano materials such as Nano clay, Titanium Di-Oxide, Nano-hydrated lime and carbon nanotubes. These materials are also safe, durable, sustainable, economical and effective in use as modifiers to enhance the properties of binders in pavements, that is engineering and rheological properties. Concerning the physical properties, decrement in penetration values of binders, enhancement of softening point values is observed while using nanomaterials in pavement constructions. Results in term of rheological properties are also promising, that is enhancement in resistance to rutting, performance grade, low-temperature cracking resistance and aging resistance.
Besides, engineering properties such as stiffness, strength, resistance to rutting, indirect tensile strength and modulus of resilience have shown improvements in properties of composite pavements. Alongside, in rigid pavements the application of nanomaterial such as Titanium Di-Oxide also demonstrate enhancing properties of the composite pavement material due to modifying nature of material as an additive in binders.
In conclusion, it is found that Nano clay is beneficial and have a propensity for enhancing the properties when added with virgin asphalt. Due to numerous types of Nano clay, it is recommended to further investigate and explore their properties to make it effective in use, as it is naturally available, safe, user friendly and have optimum cost. As the advancements in the computational and numerical methods are progressing, complexity of nanotechnology is getting simpler to understand the nature of materials in order to manipulate and exploit to enhance the material properties of the pavement constructions and processes.
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