Recycling fishing nets into concrete
Tutor / director / evaluatorOttosen, Lisbeth M.
CovenanteeDanmarks tekniske universitet
Document typeMaster thesis
Rights accessOpen Access
Annually, it is estimated that 12,7 million tons of plastic waste enters our oceans. Nowadays, particularly, the fishing industry is on the top of marine waste product generation. Over 30,000 nets are estimated to be lost in selected European fisheries annually due to bad weather conditions, gear conflict, ocean currents, and by action of fishermen. Furthermore, the plastic waste going into the ocean is not only a specific problem for the marine ecosystem, but for humans too. The microplastics created because of the degradation of waste products in the ocean are ingested by animals entering later the human food chain. Following the objective of minimizing marine waste and as part of the research for the Circular Ocean Interreg Project in the Northern Peninsula Area Region, this master thesis investigates the use of fibers from waste fishing nets thrown into the ocean as fiber reinforcement in cement mortar samples. Fiber-reinforced cement-based specimens are already widely used in the construction sector, with different kinds of fibers, from steel to natural fibers. In this project, two types of fibers were used: commercial fibrillated polypropylene (PP), already used in cement-based specimens and recycled polyethylene (PE) fibers from discarded fishing nets. The thesis is divided into two main parts. The first part is focused on reporting the environmental impact of the discarded fishing nets. The degradation of the nets was tested with a small-scale ocean water experiment simulation, in which microplastics were quickly visualized. Moreover, a characterization of the impurities as sand, seaweeds, salt and microplastics coming together with the fibers was carried out. The purpose of the analysis was to get an overview of the impurities presence in the fibers mix to have a better understanding about the need to carry out a washing process before the casting. The second part of the thesis investigates the recycled fibers in cement mortar samples in terms of mechanical properties as compressive strength, flexural strength, flexural toughness and the interface bonding between the fibers and the cement-based material matrix. Finally, concerning the plastic shrinkage prevention, the digital image correlation (DIC) method was used to measure the specimens’ microstrain and compare the values with the results achieved with the manual Linear Variable Differential Transformer (LVDT) test to prove the reliability of both test. Promising results regarding the mechanical properties were achieved for the recycled PE reinforced mortar samples, showing a similar workability comparing with the commercial PP reinforced mortar samples. This means that the commercial PP fibers, fabricated only with the concrete reinforcement purpose, could be substituted with the PE recycled fibers. In addition to a positive environment impact, minimizing the discarded fishing nets quantity, the use of PE recycled fibers could lead also to an economical benefit to the Scandinavian construction companies along with a transition to a more sustainable production.