Seagrass as a Sustainable Alternative for Building Materials: Assessing its Feasibility, Processing Methods, and Performance in Construction
Dissertation
Datum der mündl. Prüfung:2023-09-21
Erschienen:2023-12-08
Betreuer:Prof. Dr. Carsten Mai
Gutachter:Prof. Dr. Kai Zhang
Gutachter:Prof. Dr. Rupert Wimmer
Gutachter:Dr. Markus PD. Euring
Gutachter:Prof. Dr. Stergios Adamopoulos
Förderer:DAAD (Deutscher Akademischer Austauschdienst)
Dateien
Name:Doctoral thesis-Aldi Kuqo.pdf
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Format:PDF
Description:Doctoral thesis
Zusammenfassung
Englisch
Seagrasses are vital contributors to the ecosystem, absorbing atmospheric CO2 and generating oxygen for marine life. However, when they decompose, the accumulated biomass along the shores can lead to concerns like CO2 and CH4 emissions and eutrophication. Although seagrass remains are essential for local habitats, they hinder the scenic beauty of tourist beaches. Instead of landfilling this biomass, it can be transformed into building materials. This study aims to investigate the main characteristics of seagrass, suitable processing methods and combinations with several binders to produce building products. Lightweight gypsum composite materials containing seagrass fibers (Posidonia oceanica) were prepared by casting. Seagrass fibers were added to the gypsum paste at a proportion of up to 6 wt%. The seagrass-based composites were compared with pure gypsum composites and those based on wood fibers. The results revealed that at a low proportion of fibers, seagrass had no significant effect on the bending and compression properties of the composites, unlike the wood fiber composites which exhibited increased strength even compared to pure gypsum ones. Still, the inclusion of seagrass fibers led to a significant increase in the roughness of the composites. Further investigations focused on the production of fiberboards using seagrass fibers (Posidonia oceanica) as the raw material, both with Portland cement. A comparison was made between the seagrass-based cement boards and those made from wood particles. The chemical analysis of the raw materials and their effect on cement hydration was conducted prior to the production of boards. Cement powder was mixed with a large proportion of lignocellulosic material (up to 52 wt%). The blend was hot-pressed, conditioned for 28 days, and then cut into testing samples. Mechanical and physical tests were performed to evaluate the properties of the boards. Additionally, a structural analysis was carried out using a 3D digital microscope and micro-CT to examine the bonding and failure mechanisms of both intact and broken samples. The seagrass cement bonded boards exhibited much higher mechanical and physical performance compared to wood particleboards bonded with cement. The high strength and resistance to water and heat can be attributed to the morphology of the seagrass fibers, characterized by their long and flexible nature (high aspect ratio), as well as their chemical composition. Leachates released from seagrass fibers did not seem to significantly affect cement hydration, making them a compatible material for use in cement fiberboard production. Geopolymer-bonded seagrass-based boards, similar to cement bonded boards, were produced using the dry mixing-spraying process and they were compared to boards made from wood fibers. This technique allowed for the mixing and pressing of large amounts of lignocellulosic materials to obtain strong boards. The objective of this part of the study was to produce geopolymer bonded boards with high lignocellulosic content, with proportions of up to 50 wt%. Mechanical tests, including bending strength, screw withdrawal test, and internal bond tests, were conducted, along with physical tests such as cone calorimetry, water absorption, and thickness swelling. The distribution of the binder and the effectiveness of the dry mixing process were assessed through microscopy techniques such as SEM, 3D microscope, and micro-CT. The results demonstrated that seagrass-based fiberboards exhibited significantly better performance compared to wood fiberboards. It was concluded that the adequacy of mixing was influenced by the size and morphology of the mixed aggregates. Sandwich boards bonded with geopolymer binder were also produced using the dry mixing spraying process. When seagrass fibers were allocated in the outer parts of geopolymer bonded wood-based particleboards, they acted as reinforcements, resulting in an increase in the bending strength of the boards. The performance of these boards was compared to that of commercial cement boards. Besides performing mechanical and physical tests, additional investigations were conducted to assess the mixing efficiency of metakaolin and the alkaline activator. This evaluation involved adding a colorant to the alkaline activator and subsequently using microscopy investigations to analyze the geopolymer paste. The incorporation of seagrass fibers appeared to enhance the bending strength of the geopolymer sandwich boards and provided a slight improvement in fire protection. Insulation boards were manufactured using seagrass leaves and pMDI as a binder. Seagrass leaves from two species of seagrass were used in this study (Posidonia oceanica and Zostera marina). The mechanical and physical properties of the low-density boards (densities ranging from 80 to 200 kg m-3) were evaluated according to the standard requirements for insulation boards. Thermal conductivity measurements were conducted using a heat flow meter, and fire resistance was assessed through cone calorimetry and single flame tests. An economic analysis was performed to assess the production cost and profitability of seagrass insulation boards compared to those made from wood fibers. The seagrass leaves boards exhibited low thermal conductivity similar to wood fiber boards, as well as high fire resistance. Cost analysis indicated that seagrass leaves are a cost-effective alternative to wood fibers due to low raw material costs, minimal energy requirements for production, and the potential for reduced fire-retardant usage. Additionally, flexible mats were produced using Zostera marina and bicomponent fibers as a binding agent. The correlation between compression, internal bond strength, flexibility, and density was assessed through a vertical density profile analysis and microscopy analysis. These mats displayed high elasticity and a thermal conductivity ranging from 0.039 to 0.051 W m-1K-1. Overall, the use of seagrass fibers and leaves to produce building materials appears to be a promising approach for its effective utilization. After the end of life, seagrass biomass can be further utilized, extending its life cycle and promoting sustainable practices in the construction industry.
Keywords: Seagrass; Insulation materials; Composites; Ecological building materials; Mineral binders