Recycling cigarette butts in bitumen and asphalt concrete for pavement construction

Around the world, waste management has become an alarming issue. Waste products are filling up the landfill areas and reducing liveable space on the Earth. Leachate produced from landfills contaminates the surrounding environment. Cigarette butts are among the topmost littered object across continents. Globally, the number of smokers has grown to 1.3 billion. Trillions of cigarettes are being produced every year to meet the need of this large number of smokers. Resulting in a large amount of mephitic waste cigarette butts (CBs) being dumped into the environment. Researchers have discovered that CBs make up more than one-third of the total littered waste on the planet. Every year more than 4.5 trillion CBs are accumulating in the landfill system in the world. CBs take years to biodegrade and contain the cellulose acetate based filter, tar, nicotine, tobacco, and many highly toxic chemicals. Over time, those toxic chemicals leach to soil and waterbody, proceeding contamination and toxicity. Mohajerani et al. in 2017 developed the encapsulation method for CBs with bitumen and paraffin wax and evaluated the utilization of encapsulated CBs in dense graded asphalt (DGA) using bitumen class C320, C170, and C600. Physio-mechanical properties of the DGA were investigated and concluded with promising outcomes, and the scope for further development of the research was outlined in the parent research. This research focused on two unique approaches to recycling CBs in asphalt pavement as a continuation and expansion of the parent research. The first novel approach was to recycle CBs as fiber modifiers for bitumen. CBs were pre-processed and mixed with bitumen classes C320, C170, and PMB A10E as fiber modifier. A comprehensive laboratory investigation, including penetration test, softening point test, and viscosity test, was performed along with a binder drain-off test to evaluate the performance of the modified samples. During this investigation, samples were prepared with 0.3% cellulose fiber, 0.2%, 0.3% 0.4%, and 0.5% CBs. Advanced rheological tests like complex modulus and relationship with frequency, temperature, and phase angle were established, and the Linear Amplitude Sweep (LAS) tests were performed to assess the fatigue damage resistance criteria of CB fiber modified bitumen. Stone mastic asphalt (SMA) samples were prepared with CB fiber modified bitumen, and the Marshall Stability and Flow of SMA were investigated and compared with the control sample prepared with conventional virgin cellulose fiber modified bitumen. The results from this investigation met industry standards and supported the use of CB fiber modified bitumen in the construction of SMA instead of virgin cellulose fiber. In the second recycling approach, the encapsulation method was improved using Polymer Modified Bitumen (PMB) A10E, and improved BECB were utilized to prepare SMA and DGA samples. SMA samples were prepared by replacing coarse aggregates by 1%, 2%, and 3% (by weight) with BECB. Marshall stability, flow, resilient modulus, and volumetric properties of SMA manufactured samples were investigated, and the results were compared with those of the control SMA samples prepared without BECB. Outcomes from the investigation indicated that the use of BECB in SMA improved the stability and resistance to permanent deformation. As further development and confirmation of the parent research, investigation on the utilization of improved BECB in heavy-duty DGA prepared with PMB class A10E has been carried out to understand the effectiveness of the encapsulation method. Marshall Stability, Flow, Resilient Modulus, Dynamic Creep, Tensile Strength Ratio (TSR), and Indirect Tensile Fatigue tests were performed to evaluate the performance of BECB modified DGA. Results were compared with control DGA prepared without BECB. Test results suggested that DGA samples prepared with 0.5% and 1% BECB met industry requirements and endorsed the recycling method of CB in asphalt concrete. Leachate from CBs and BECB were collected at pH 2.9, pH 5.0, and pH 9.2 to investigate the efficacy of the encapsulation method in trapping heavy metals. Leachate analysis result from Inductively Coupled Plasma Mass Spectrometry (ICP-MS) indicated that the encapsulation method has successfully trapped approximately 90% of heavy metals present in the CBs. Detected heavy metals in the leachate were insignificant compared to the Victorian Environment Protection Authority limit and can be categorized as non-hazardous. Microstructure analysis of CBs and BECB confirmed the uniformity of the encapsulation method using Leica Optical Microscope and Bruker X-Ray Micro Computed Tomography system. The thermal conductivity of BECB modified asphalt concrete has been investigated, and the potential for energy savings in the manufacturing process has been observed. This research has discussed the global CBs pollution issue, prospective solutions to this problem, and scope of expansion and further development. Outcomes of this comprehensive research work have been published in seven journal articles and presented in two international conferences as outlined in Appendix A.