Strength, durability and microstructural analysis of concrete incorporating waste carpet fibre and palm oil fuel ash

Fibre reinforced concrete (FRC) is a conventional concrete mix that contains cement, coarse and fine aggregates and a dispersion of discontinuous short fibres that are randomly distributed in the fresh concrete mix. The fibres improve the ductility, energy absorption and tensile and flexural strengths of concrete mixture. With the increasing amount of waste generation from various processes, there has been a growing interest in the utilization of waste in producing building materials to achieve potential benefits. In the construction industry, the idea of sustainability encourages the use of waste products to replace raw materials, such as fine and coarse aggregates, cement and fibrous materials. This leads to sustainable, green and environmentally friendly construction by reducing the price of the components compared to disposing of the materials. This research, therefore, focuses on the effects of waste carpet fibre (WCF) and palm oil fuel ash (POFA) as partial replacements of ordinary Portland cement (OPC) on the fresh and hardened properties of concrete. Six volume varying from 0-1.25% of 20-mm-long carpet fibre were used with OPC concrete mixes. Another six mixes were made that replaced OPC with 20% POFA. The water/binder (w/b) ratio of 0.47 was kept constant in all mixes. Fresh properties of concrete were studied with respect to its workability in terms of slump values and Vebe time, unit weight, air content and heat of hydration. The hardened properties examined are; mechanical strengths, deformation characteristics and durability properties. Various techniques, including the use of scanning electronic microscope (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study the microstructure of the concrete. A 3-phased investigation revealed that both carpet fibres and POFA have a potential to be used in the development of concrete properties. The combination of WCF and POFA decreased the slump values and increased the Vebe time of fresh concrete. The unit weight and air content significantly decreased, while the heat of hydration was also reduced. The inclusion of carpet fibre to either OPC or POFA concrete mixes did not improve the compressive strength and modulus of elasticity at early ages. At later ages, however, the compressive strength of the mixtures containing POFA significantly increased and the obtained values were higher than that mixes with OPC alone. The positive interaction between carpet fibres and POFA leads to high tensile strength, flexural strengths and impact resistance, thereby increasing the concrete ductility and toughness with higher energy absorption and improved crack distribution. The creep and drying shrinkage were also considerably reduced. The durability and microstructural characteristics of the respective FRC were significantly improved. The study showed that the use of waste carpet fibre and palm oil fuel ash in the production of sustainable green concrete is feasible both technically and environmentally