Structural Performance Characteristics of Flax Fabric-Reinforced Epoxy Pipes

Abstract

Worldwide the construction industry uses more than three billion tons of raw materials every year, which represents approximately 40% of global raw material consumption, and is also responsible for 30% of global greenhouse gas emissions. Pipeline services are an unceasingly growing market, with commonly utilised pipes being manufactured from non-sustainable sources. Increasing worldwide environmental consciousness continuously pushes governments and corporations to look at new construction materials, with reduced consumption of raw materials via the use of renewable or waste materials being considered as a significant step to achieving a more sustainable construction industry. Natural fibres are readily available in many countries, and there is considerable potential for their application as a sustainable construction material, with flax fibre having shown substantial potential as an alternative material to replace synthetic fibres in polymer composites. Flax fibre-reinforced epoxy (FFRE) has been shown to have close similarity in specific tensile modulus with glass fibre-reinforced epoxy (GFRE) composites, and research on different structural components reinforced with or manufactured from FFRE have shown a substantial potential for FFRE composites to be used in structural components. This study provides a comprehensive understanding of the design and characterisation of FFRE composite pipes. Initially, a methodology that was based on manual fabric winding technique was developed to manufacture FFRE pipes. The application of FFRE pipes presents many advantages over the use of conventional pipe products namely, corrosion-resistance and convenience for pipe transportation and installation when compared to steel and concrete pipe counterparts and more sustainability when compared to plastic pipes. Buried pipelines are subjected to significant lateral compression due to the weight of the soil above the pipe (dead load) or resulted from the trucks or other vehicles traversing the pipeline at the ground surface (live loads). In the next chapter physical and mechanical properties of flax fibre and FFRE composites with varying fabric layers were investigated and then the structural performance of FFRE pipes with varying diameters and fabric layers that were subjected to lateral compression loading was discussed. The FFRE pipes showed higher strength, flexibility, and specific energy absorption when compared to pipes manufactured from different natural fibre composites, while demonstrating comparable strength, specific strength, and specific energy absorption to synthetic and hybrid fibre composite pipes. Bending action can arise within elevated aboveground pipelines due to the weight of the pipe material and the containing fluid, from wind and earthquake loadings, and from pipe foundation subsidence. For aboveground pipes resting on the ground, pipe free spanning, which may be developed over time due to soil erosion or scouring, can lead to bending actions on pipelines. In underground pipelines, seismic shaking, liquefaction, fault movement, lateral ground movement, and ground differential settlement due to excessive traffic loading lead to bending actions on pipelines. The structural performance characteristics of FFRE pipes of varying diameters and flax fabric layers when subjected to bending were investigated, with the results demonstrating that the FFRE pipes had deformation capability that was greater than for pipes manufactured from synthetic fibre composites while FFRE pipes showing maximum bending moment that was comparable to the maximum bending moments of synthetic fibre composite pipes. External interferences are identified as a primary reason for the failure of pipelines. Contact of pipe wall with remaining pieces of rock within a buried pipe trench and earthmoving operations, specifically digging by excavators, are considered potential sources of external interferences to pipelines that may cause indentation or piercing of the pipelines. Indentation and piercing experiments were performed on the FFRE pipes using varying indenter nose shapes, and the effect of fabric layers and pipe diameters on stiffness, strength, deformation, and service and structural failure mechanism of the FFRE pipes was established. Internal pressure is considered one of the primary stress sources in pipelines, and the ability of a pipe to safely sustain service-level internal pressure is considered one of the major features of pipe engineering design and integrity assessment. In the next chapter FFRE pipes that had varying diameters and numbers of flax fabric layers were subjected to internal pressure loading, with the results showing that the pipe internal pressure that was associated with pipe leakage and pipe bursting exceeded the typical pipe pressure range for domestic use, for water distribution, and for long-distance water transmission by a wide margin based on current practice. Pipelines subjected to dynamic excitations fail in the pipe body due to tension, compression, and bending actions. Therefore, determining stresses in the straight segments of pipelines when subjected to dynamic ground motions is crucial concerning pipe safety design and seismic risk assessment. In chapter 8, dynamic and seismic performance characteristics of a free-spanning FFRE pipe that had varying extent of water content when subjected to harmonic and earthquake ground motions of varying characteristics were investigated. The pipe remained below yield limits of the material for all the ground motions tested, and no service or structural failure was detected in the pipe. Overall, FFRE pipes were effective in transmitting water and represented a significant potential as a viable alternative to the use of pipes constructed from conventional materials.