This study investigates the effects of mixing Polypropylene waste plastics in the bituminous mix for the design of Flexible Pavement. Since, obtaining Marshall Test results from the bituminous mix is time-consuming, so if the practitioners measure the values of stability and flow by mechanical testing, other computations can be done by applying simple mathematical calculations. So, this study carried out stability and flow tests on different specimens made with varying bitumen and polypropylene plastic content. From the initial test results, the optimum bitumen and plastic contents are found. Further, the test results obtained from Marshall Test are modelled by identifying various input variables, which are various physical properties of the mix such as plastic content, bitumen content, air voids and unit weight. The regression modeling framework is adopted in this study to predict the Marshall stability and flow value. Since the developed models have yielded good results, these can be effectively used in parameter estimation, and thus aids the future researchers.
TopIntroduction
The rapid growth in industrialization coupled with population growth has led to enormous rise in production of various types of wastes worldwide. In a recent study concerning the top 20 countries that have dumped the most plastic waste into the oceans, India (at 12th) is one of the worst performers. It has dumped up to 0.24 million tons of plastic waste into the ocean every year, thereby polluting the natural resources. One recent study (2014-15) reported that approximately 8 kg of waste plastics dumped by the each individual in India. These plastic wastes are needed to be recycled, if not, it gets disposed by the available waste disposal techniques like Land filling and Incineration. Though these techniques have been widely in use but these too have certain impacts on the environment which are discussed as under.
Land filling refers to a process of disposal wherein the waste materials are buried in a specific area that is situated far away from the city. This process has certain impacts on the environment like affecting water recharge, reducing soil microbial activity, and also it leads to drainage and water line clogging. Such clogging in turn leads to production of gases such as methane, which affects Greenhouse effect. Also, land availability for filling is a major point of concern. Further, Incineration refers to a process of burning the wastes above 700°C. Incineration of polymers like polypropylene, polystyrene, etc. evolves gases like CO2, CO etc. which in turn causes global warming, pollution. If polyvinyl chloride mixes with the waste, it results in the production of Chlorine, HCl and sometimes Dioxin which is a carcinogenic and a poisonous gas. In fact, this process requires scientific monitoring and it can accentuate pollution problems, if strict standards aren’t being enforced.
Since both landfilling and incineration have certain negative impact on the environment. Under these circumstances, an alternate use for the waste plastics is the need of the hour. Several investigations in India and many other countries have revealed that properties of bituminous mixes can be enhanced to meet the present requirements of pavement with the inculcation of certain additives in bituminous mixes. These additives are termed as “Bitumen Modifiers” and the bitumen that is premixed with these modifiers is termed as “Modified Bitumen”. Modified bitumen is expected to provide higher strength and durability depending upon the type of additives used and modification process involved. The time period of next renewal is expected to be extended by 50 percent in case of surfacing with modified bitumen in comparison to normal period specified for conventional bituminous mix. Certain Performance analysis studies undertaken under the protection of Central Road Research Institute, New Delhi; Highway Research Station, Chennai; Rubber Board, Kottayam (Kerala); Ministry of Road Transport and Highways, New Delhi; Kerala Public Works Department and Gujarat Engineering Research Institute, Vadodara have revealed that the usage of Modified Bitumen in construction as well as maintenance of bituminous roads is quite cost effective, when life-cycle cost is taken under consideration.
Plastic waste when mixed with hot bitumen, it melts to form an oily coat over the aggregate and the mixture is laid over the road surface as similar as a normal tar road. The plastic waste can be effectively used as a binder material in flexible pavements. They may be used to enhance strength, enhance fatigue resistance to deformation and thus makes the pavements more durable. Plastic coated bitumen can result in higher stiffness than that of conventional bitumen, but without undergoing a large increase in flexibility.