Project no. 406
Circular Ocean - Recycling Fishing Nets into Concrete
DTU Byg: Institut for Byggeri og Anlæg, Technical University of Denmark
Annually, it is estimated that 12,7 million tons of plastic waste enters our oceans. Nowadays,
the fishing industry is on the top of marine waste product generation. Over 30,000 nets are
lost by European fisheries annually due to bad weather conditions, gear conflict, ocean
currents or by action of fishermen. 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.
Figure 1: Logo of Circular Ocean project
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 first part of the thesis is focused on reporting the environmental impact of the
discarded fishing nets, testing the degradation of the nets with a small-scale ocean water
test simulation, where the microplastics generation was 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 why they should
be removed before the casting process.
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 interface bonding between the fibers and the cement-based material matrix.
Finally, concerning the plastic shrinkage prevention, digital image correlation (DIC) was
used to analyse the specimens’ microstrain and compare the results with the manual LVDT
test to prove the reliability of the test.
Promising results regarding the mechanical properties were achieved for the recycled fibers
samples, showing a similar workability as the commercial PP fibers samples fabricated on
purpose for the concrete reinforcement. Furthermore, in addition to a clearly positive
environmental impact, the cost analysis showed that the use of recycled fibers could lead
also to an economical benefit for the construction sector.