Performance of sustainable fibre reinforced cementitious composite incorporating recycled synthetic textile waste
Creators: name: TRAN, Nghia
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400505
subject: Construction materials

description: The disposal rate of textile waste in the landfill has reached an alarming level worldwide. In the last decade, the exponential accumulation of textile waste disposal has had a far-reaching impact on the environment and in the socio-economy. To this end, upcycling textile waste fibres for construction and building applications is seen as a beneficial resolution for both the textile and construction industries in a bid of closing the loop towards a circular economy.

This research study aims to develop a fundamental understanding of the effects of recycled textile fibres, from fabric and carpet waste sources, on the performance of cementitious composites. An intensive literature review was implemented in the initial research to determine the dual effects of textile microfibres on energy-absorption via bridging action (direct mechanism) and changes of pore structure (indirect mechanism). Following this initial research an experimental programme was designed and executed to analyse the influence of textile fibres on strength properties, toughness, flowability and drying shrinkage. Microstructure, pore characteristics and fibre-matrix interfacial properties were characterised using X-ray micro CT and nanoindentation to comprehend the underlying mechanism affecting the performance of the fibres. A total six types of recycled textile fibres were investigated in this study, separated into two phases. The first phase targeted four recycled textile types from fabric waste, while the second phase focused on two textile fibres from carpet waste. In each phase, the effect of single and hybrid fibres on mechanical properties and microstructure were analysed to optimise performance and identify the parameters which influence the cementitious matrix properties.

In the first phase of the research, an optimisation process was initiated for the four individual fibres (i.e. Kevlar, Nomex, Cordura Nylon, and PBI). In addition to conventional single fibre, two-dimensional fibre with specific length and width - so-called "2D woven fibre" was also investigated in the optimization process. Fabric fibre parameters include fibre content (0.1%, 0.3%, and 0.5%), fibre length (6, 12, and 24 mm) and 1D fibre (width of 0) vs. 2D woven fabric fibre (width of 3 and 6 mm). The results indicated that the inclusion of 2D woven fabric fibres can enhance compressive and flexural strength, but also increase the drying shrinkage rate of the cementitious matrix. The highest strength improvement and shrinkage resistance of cementitious composites were recorded corresponding to the incorporation of 1D fabric fibre, irrespective of fabric type. The optimum performance was observed at a volume fraction of 0.3% and length of 12 mm. In hybrid case, six different hybrid fibre combinations, namely Kevlar/Nomex, Kevlar/Nylon, Kevlar/PBI, Nomex/Nylon, Nomex/PBI, and Nylon/PBI fibres were investigated at three different blend ratios (2:1, 1:1, and 1:2). It was found that the optimum mechanical performance of cementitious composite correlated to the addition of hybrid Kevlar/Nomex, Kevlar/Nylon and Nomex/Nylon fibres at a ratio of 1:1, but a ratio of 1:2 for Kevlar/PBI, Nomex/PBI and Nylon/PBI fibres. At the same optimised fibre content and length, the incorporation of hybrid textile fibres achieved equivalent strength properties and shrinkage reduction rate to that of the single textile fibres.

In the second phase, two types of carpet fibre (i.e. PP and PTT) were investigated. The optimum parameters which provided the greatest strength improvement in the cementitious matrix was recorded with a volume fraction of 0.5% for PP fibre and 0.1% for PTT fibre, and length of 12 mm. The use of hybrid PP/PTT carpet fibre (0.4% PP + 0.1% PTT) achieved greater enhancement in strength properties and shrinkage mitigation than that of optimised PP and PTT carpet fibres alone. This indicated the possibility of combining fibres to manufacture reinforcing cementitious composites with a comparative or better performance than with the incorporation of single fibres alone.

One of the key factors modifying microstructures and performance of cementitious composites is the hydrophilic or hydrophobic characteristics of the fibres. Pore refinement was pronounced for presence of hydrophilic textile microfibres. This is attributed to an increment in viscosity (low flowability) which hindered the coalescence of air bubbles into larger pores and subdivided macropores into finer pores due to a dense network of textile microfibres. This also renders hydrophilic textile fibres more disadvantageous in shrinkage mitigation than hydrophobic textile fibres due to a higher quantity of fine pores which are subjected to shrinkage-induced tensile stress. It was found that the hydrophilic Kevlar and Nomex fibres tended to have a smaller ITZ thickness (10 micro meters) than hydrophobic PBI, Cordura Nylon, PP and PTT fibres (15 micro meters). A high proportion of voids (beyond 50%) and a small quantity of clinker was found within 60 micro meters of all textile fibres at the early 7 day age. Nonetheless, the formation of hydrated C-S-H and CH phase rendered microstructure denser with increased curing time. The constrained area within the network of microfibres appears to limit the growth of plate-like portlandite crystals (CH) with only a small volume fraction recorded near all textile fibres. These research results provide an extensive data base and an insight into the effect of the six textile waste fibres on the performance and microstructure of cementitious mortar. This paves a way for further use of recycled textile fibres as reinforcing elements for cementitious composites in lieu of disposing of the fibre wastes in landfill.