An investigation into the use of recycled carpet waste fibres to reinforce concrete

Abstract

"The topic of this dissertation is the use of post-consumer carpet waste polypropylene fibres instead of virgin polypropylene fibres as reinforcement in mass concrete. Carpet waste is a recyclable and re-useable material with a bountiful supply readily available that can be diverted away from going into landfill. Research examining the use of carpet waste fibres in concrete mixes incorporating a percentage of cement being replaced by ground granulated blastfurnace slag (GGBS) needs investigating. The main aim and objectives of this study are to compare the use of carpet waste polypropylene fibre mixes against virgin fibre mixes and a control mix all containing GGBS at 25% of the mass of cement. The basis for the comparisons will be compressive strength and can the carpet waste fibres offer the same results or better as virgin fibres in concrete mixes as they would provide a more sustainable alternative. Finally, does the polypropylene fibre dosage rate have an effect on the strength grade of mass concrete? A quantitative methodology was utilised for this research as the most appropriate way for questioning the aim and objectives due to the mode of data capture being through the use of laboratory experimental work. Five different concrete mix designs were made and four types of test performed on the mixes to ascertain the relevant data. One wet test, the slump test was performed to check the workability of the mixes and the three hardened tests, compression, pull-out and rebound hammer, to allow the compressive strengths of the different mix designs to be compared. The main findings of this study were that carpet waste fibres used in mass concrete containing GGBS provided similar compressive strengths to virgin fibres mixes at low dosages and a control mix. At higher dosage fibre levels the carpet waste fibre mix showed lower compressive strengths compared to the lower dosage mixes but still sufficient to exceed the target strength and match the equivalent virgin fibre mix. Workability deteriorated with increased dosages of fibres. In conclusion post-consumer carpet waste polypropylene fibres can offer a viable alternative to virgin polypropylene fibres when used for reinforcement of mass concrete based on the research undertaken for this study.