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• Kenaf fibre (KF) is used to produce an environmentally friendly composite. • The effect of the content and length of kenaf fibre on the durability properties of geopolymer concrete is reported. • KFRGC with longer length and higher volume fraction of KF exhibited lower durability performances. The use of fibres in concrete has attracted the interest of many researchers to improve the tensile properties of geopolymer concrete. While adding natural fibres has gained popularity as an eco-friendly alternative to synthetic fibres. This combination of natural fibre-reinforced geopolymer concrete is an interesting composite that has not been reported by many, particularly when kenaf fibre is applied. Hence, this article aims to understand the performance of kenaf fibre-reinforced geopolymer concrete (KFRGC) in terms of water absorption, porosity, sorptivity, water penetration, and resistance against chloride ions penetration and chemical attacks. The results showed that the addition of KF increased the porosity of the geopolymer, thus increasing the water absorption-related properties. It's observed that the porosity tends to increase with increasing length and volume content of fibres. Compared to control specimens, the highest increment (12.5%) in the porosity was recorded with specimens prepared with a 1.5% volume of fibre and a length of 40 mm. Likewise, the water permeability reading increased with increasing volume and fibre length in the geopolymer matrix. In specimens containing 1.5% fibre, increasing the length of fibre from 20 to 30 mm caused an increment in water permeability from 7.42 cm to 8.9 cm, respectively. However, the chloride, sulphate and acid resistance could be improved due to the ability of the fibres to bridge across the cracks. Furthermore, increasing the length of the fibre to 40 mm, reduced the acid resistance of the proposed concrete and increased the loss of strength to 16.3% and 19.2% at the age of 180 and 365 days, respectively. The outcomes of this research show that using kenaf fibres as a fibrous material in the production of environmentally friendly and durable concrete has a promising future. [ABSTRACT FROM AUTHOR]

• Sustainable geopolymer concrete using FA and GGBS, with the addition of kenaf fiber was produced. • Effects of kenaf fiber length and volume fraction on the engineering properties of geopolymer concrete were studied. • Mechanical properties of the composites were predicted via Surface Response Approach. Sustainable construction materials are in needs to reduce CO 2 emissions in the environment. Geopolymer being an emergent sustainable construction material had been extensively studied. However, its brittleness is still the main issue to be overcome. Hence, in this research, natural kenaf fiber (KF) as environmental-friendly low-cost material is introduced to enhance the overall quality of the geopolymer. This study introduces a potential sustainable construction material called Kenaf Fiber-Reinforced Geopolymer Concrete (KFRGC) which is studied via experimental tests and statistical modelling. The effects of 20 mm to 40 mm lengths and 0.75 % to 1.5 % volume fractions of kenaf fibers on the engineering properties of KFRGC were measured. The splitting tensile strength and flexural strength of KFRGC were observed to improve without any significant increase in the compressive strength. At 28 days of curing age, KFRGC prepared with 30 mm long, and 1.25 % volume fraction of fiber showed a 20 % and 27 % increase in splitting tensile strength and flexural strength, respectively, compared to the plain geopolymer. Furthermore, the model predicted and experimental results closely matched (less than 5 % inaccuracy). It is concluded that natural KF-included concrete can be used as an eco-friendly and sustainable building material. However, the durability aspect must be studied before it can be commercially used. [ABSTRACT FROM AUTHOR]