The highest amount of waste collected on beaches worldwide belongs to cigarette butts. According to the World Health Organization, global cigarette production reached nearly 5.2 trillion sticks in 2020. The consumption of this volume of cigarettes, resulting in approximately 1 billion tons of cigarette butts contaminated with 4000 chemicals and hazardous metals, contributes to ecological pollution and disrupts the food chain (Dobaradaran et al. 2018, Kurmus and Mohajerani 2020, Conradi and Sánchez-Moyano 2022). Iran's share, with approximately 1.1% of the world's population, includes 90 thousand tons of contaminated cigarette butts, mainly discarded in urban areas, coasts, seas, and along rivers. Studies indicate that the decomposition of fibers and plastics present in cigarette butts takes more than a decade, and each of these butts has the potential to pollute one squre meter of the environment until decomposed (Novotny et al. 2009, Smith and McDaniel 2011). The majority of fibers in cigarette filters are intertwined cellulose acetate fibers with high moisture absorption capabilities. Their natural decomposition begins 3-4 months after disposal, and often, it is a partial process. To mitigate the environmental and economic impacts of this non-degradable substance, researchers have conducted studies on recycling and reusing it in various industries such as paper, metallurgy, agriculture, pharmaceuticals, energy production, and construction (Assres and Abate 2018, Stigler Granados et al. 2019, Yousefi et al. 2021, Koroleva et al. 2021, Yousefi Nasab et al. 2022). Additionally, civil engineers are contemplating the use of this slow-degrading material in construction or road-building, although there have been relatively few studies on the management and recycling of this hazardous waste.
Mohajerani et al. conducted a research study to address the issue of cigarette butt waste, utilizing it as a component in fired clay bricks (Mohajerani et al. 2016). They incorporated 2.5%, 5%, 7.5%, and 10% by weight of collected cigarette butt waste into the clay bricks and compared the results with bricks without cigarette butt content. The mixing time and the rate of temperature increase were examined in this study. The findings revealed that approximately 58% of the energy required for producing clay bricks could be saved through this process. In another research, Mohajerani et al. encapsulated discarded cigarette butts in the environment with paraffin and bitumen and investigated their use in asphalt concrete (Mohajerani et al. 2017). The idea behind encapsulating cigarette filters was to limit the interaction of cigarette butts with liquids and prevent chemical changes in asphalt concrete. They examined the physical and mechanical properties of asphalt concrete based on the amount of encapsulated cigarette butts with paraffin or bitumen per unit volume, comparing it with asphalt concrete without cigarette butts. According to the results of this research, when using 10 or 15 kilograms per cubic meter of encapsulated cigarette butts in the mix design, the produced asphalt concrete meets the regulations for light, medium, and heavy traffic. This is in contrast to asphalt concrete produced with paraffin-encapsulated cigarette butts, which is only suitable for light traffic. Lou et al. conducted a study investigating the changes in compressive strength of concrete mixes incorporating cleaned and paraffin-treated cigarette butts (Luo et al. 2019). They prepared cigarette butt filters in six mixing designs, including 5, 7.5, 10, 12.5, 15, and 20 kilograms per cubic meter of cigarette butt content, and compared their 28-day compressive strength with concrete without cigarette butts. The results indicated a reduction in the 28-day compressive strength ranging from 5% to 30% compared to the concrete without cigarette butts. Additionally, there was a suitable linear relationship between these two variables. Rahman et al. explored the possibility of using fibers collected from discarded cigarette butts in asphalt and bitumen in their study (Rahman et al. 2020). In this research, cigarette butt fibers were utilized in three different bitumen grades as modifiers to enhance asphalt behavior. The examination of the results of permeability, viscosity, and softening point tests on samples containing 0.3% cellulose acetate fibers, as well as 0.2%, 0.3%, 0.4%, and 0.5% fibers from cigarette butts, indicates a significant improvement in the physical and rheological properties of modified bitumen with fibers. In a study conducted in 2021, Yuan et al. added recycled cigarette butts in weight ratios of 0.5, 1.0, and 1.5 percent to unfritted ceramics, comparing the results with ceramics without cigarette butts (Yuan et al. 2021). This investigation focused on the chemical and mineralogical characteristics, density, shrinkage, water absorption, fracture resistance, and flexural modulus of the ceramic tiles. The findings revealed that the substitution of 0.5 percent by weight of cigarette butts exhibits better performance compared to other ratios and meets the requirements of the AS13006 standard. It's worth noting that the cigarette filters used were initially subjected to 24 hours of heat treatment at 105 degrees Celsius to eliminate moisture, disinfect them, and then the fiber mix was separated using a fiber mixer. Kurmus and Mohajerani investigated the energy savings, thermal conductivity, porosity, and micro- and macro-properties of fired clay bricks with cigarette butt waste (Kurmus and Mohajerani 2021). In the brick mix design, 0%, 2.5%, 5%, and 10% of cigarette butt fibers were used. Based on the obtained results, the addition of cigarette butt fibers significantly affected the thermal conductivity of the clay bricks. Furthermore, with the application of 1% cigarette butt fibers, approximately ten percent energy savings were achieved.
Concrete is the most widely used material after water. However, incorporating materials that contribute to environmental pollution into concrete consumption can be a suitable solution to reduce their hazards. Therefore, this research explores a solution for incorporating discarded cigarette butts into concrete. The study aims to investigate the effect of adding cellulose acetate fibers derived from cigarette butts on the compressive, tensile, and flexural strengths of silica fume concrete. Additionally, it examines the impact of these fibers on increasing ductility and preventing the rapid propagation and growth of cracks in fiber-reinforced concrete. To achieve this, collected cigarette butts were washed, dried completely at a greenhouse temperature of 95 degrees Celsius, and the cellulose acetate fibers were spinning off and isolated from them. To compensate for potential decreases in the mechanical properties of cellulose acetate fiber-containing concrete, microsilica, equivalent to 11% of the weight of cement, was added to the concrete. This addition aims to modify and enhance the cement paste's adhesion to the fibers in addition to improving compressive, tensile, and flexural strengths. To determine the optimum amount, cigarette butt fibers were added to silica fume concrete containing sand, cement, water, microsilica, and a superplasticizer in volume ratios of 0, 0.1, 0.2, 0.4, 0.5, 0.6, 0.8, 1, 3, and 5%. The optimal percentage of fiber application in concrete was introduced based on the results of experiments and the evaluation of SEM images regarding the distribution and adhesion of fibers to the cement paste.