Performance evaluation of bitumen modified by various types of waste plastics
Introduction
The increase in world population has led to a parallel and gradual increase in the demand for transportation. Because highways provide access to nearly everywhere, they are still the most commonly used transportation systems in the world for both passenger and freight transportation [1]. However, the increasing demand for transportation also leads to the rapid deterioration of highway pavements. The main approach used for preventing the deterioration of pavements is improving the properties of materials used for constructing highways [2]. Bitumen is a construction material used as binder in flexible pavements. The behavior of bitumen varies depending on vehicle speed and temperature. At high speeds and low temperatures, bitumen behaves more like an elastic solid. Under such conditions, the most commonly occurring type of deterioration is thermal cracks. At low speeds and high temperatures, on the other hand, bitumen behaves rather like as a viscous liquid, in which case the most common type of deterioration is wheel tracking. At normal environmental conditions and average speed values, bitumen exhibits viscoelastic properties, in which case the most common type of deterioration is fatigue cracks.
Bitumen is generally used in a modified form to minimize the effects of increasing traffic loads and adverse weather conditions. These modifiers improve the properties of bitumen, and thus the properties of the hot-mix asphalts (HMA) used in flexible pavements [3]. Polymer-based additives are frequently used for the modification of bitumens, and there are numerous studies in the literature on this subject [4], [5], [6]. Due to the high costs of the polymer-based additives, the use of waste thermoplastics is currently being considered for bitumen modification.
Plastics are low-density (that is, light-weight), durable, formable and low-cost materials which, owning to their properties, are widely used in many areas, sectors and industries. There are seven types of plastics:PET (polyethylene terephthalate), HDPE (high-density polyethylene), PVC (polyvinyl chloride), LDPE (low-density polyethylene), PP (polypropylene), PS (polystyrene), other types of plastics .
Disposed plastics materials do not decay, corrode, or dissolve. For this reason, they can remain intact in nature for many years. This undesirable feature results in the formation of considerable environmental pollution. However, plastic is also a recyclable material. The recycling of plastics not only allows the effective use of increasingly diminishing natural resources, but also reduces the amount of wastes that need to be buried underground, thus minimizing environmental damage. The modification of bitumen with plastics-based additives would allow additive materials to be provided at very low costs, while also permitting the utilization of waste plastics in nature. There are numerous studies in the literature regarding the modification of bitumen with waste plastics materials [7], [8], [9]. Kumar and Garg [10] investigated rheology of waste plastics-fiber bitumen. They found that, the properties of bitumen such as penetration, softening point and ductility were improved with the addition of the waste fiber. Also the optimum ratio of the fiber was found to be 0.5% on the basis of PG (Performance Grade) 70 in this study. Costa et al. [11] modified bitumen with different plastics wastes, namely polyethylene (high density (HDPE and low density LDPE), ethylene-vinyl acetate (EVA), sytrene-butadiene-styrene (SBS), acrylonitrile–butadiene-styrene (ABS) and crumb rubber. They investigated the especially storage stability of modified bitumen. The experiential tests performed in the study were penetration, softening point, dynamic viscosity and storage stability. They found that, SBS, EVA, or alternatively HDPE have showed good performance according to storage stability.
As PVC – which is a type of plastics – is an economic and easily installed material, it has recently replaced wood and concrete as construction material in many areas of the building sector. More than 50% of all PVC in the world is currently being used in the construction sector. In the United States, building and construction applications account for an estimated 75% of all PVC consumption. In the European Union, 60% of PVC is used in building and construction applications, with an additional 25% in appliances, electronics, and furniture [12].
Due to its great tourism potential and the high number of immigrants it receives every year, Antalya (Turkey) is a touristic city in which extensive construction activities are conducted. These extensive construction activities result in the production of considerable amounts of construction material wastes, which in turn lead to considerable environmental pollution. For this reason, in this study it is aimed to use PVC based construction material wastes to modify bitumens and improve their properties. To this end, a plastics waste material recycling facility in Istanbul was visited in order to obtain information regarding the three types of PVC based construction materials which are most frequently disposed of as waste material. Officials at the facility informed that the most common PVC based wastes were PVC window, PVC blinds and cable; it was hence decided that these materials would be used for bitumen modification purposes. Although all three of these waste materials are PVC based, the methods used for their manufacture are slightly different, which results in different structural properties for each one. In order to obtain the raw material for PVC blinds, for instance, calcite is added to PVC, which makes PVC harder and more brittle. To obtain the raw material for cable, on the other hand, dope oil is added to PVC, which makes PVC more flexible and formable. Finally, in order to obtain the raw material for PVC window, titanium-dioxide or barium-sulfate is added to PVC, which increases its workability. Experimental studies were thus planned to determine how each waste material affected bitumen properties. Superpave tests are commonly performed in modified bitumen studies [13], [14], [15]. These tests allow the identification of the behavior of pure and aged binding materials under the effects of compression, laying, high temperatures and low temperatures. This study aims to investigate and compare effects of waste plastics (window, blinds and cable waste) based PVC on the rheologic properties of bitumen.
Section snippets
Materials
The binders were prepared with a pure bitumen having 160/220 penetration grade. The pure bitumen was obtained from Turkish Petroleum Rafineries Corporation (TUPRAS). Table 1 gives a summary of the results of some tests performed on the pure bitumen.
In this study, the waste plastics to be used as modifiers in 3 groups of ground PVC window, PVC blinds and PVC cable were obtained from a recycling facility in Antalya in the powder form.
Preparation of samples
In this study, modifying process of the bitumen was basically
Conventional bitumen tests
Conventional tests were first conducted in order to identify effects of waste PVC additives on physical properties of bituminous binders. The results obtained using conventional test methods both before and after short-time ageing are summerized Table 2, Table 3, Table 4. As can be seen also in the tables, the penetration values for the modified bitumens are lower than pure bitumen. This means that the modification process for the bitumen resulted in hardening of binder regardless of the which
Conclusions
In this study, the effects of three PVC based waste materials on a bitumen with an original penetration value 160/220 were examined in terms of penetration, softening point, rotational viscosity (RV), dynamic shear rheometer (DSR), and bending beam rheometer (BBR) tests. As a result of the modifications for all three type modifiers, it was seen that with increasing amounts of additives, the penetration values decreased and softening point values increased. This implies that the bitumen tends to
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