Effects of Kenaf Fibre on Fresh Properties of Fibrous Concrete

Abstract

As a result of global quest for sustainable materials to achieve a bio based economy and low carbon foot print environment, the use of fibre to produce fibrous concrete composite has continuously received significant research attention. While several researches have been conducted on metallic and synthetic fibrous concretes, they exhibit several unavoidable drawbacks and bio fibrous concrete has proven to be a better alternative. Therefore, the effect of fibre volume fraction and fibre length on fresh properties of concrete was investigated. The bio fibrous concrete mix was made of six different fibre volume fractions (0.25%, 0.5%, 0.75%, 1%, 1.5% and 2%) and corresponding three different fibre lengths of 25 mm, 50 mm and 75 mm. A concrete mix proportion of grade 30 N/mm2 at 28 days target strength was prepared. A total of 19 different concrete mixes comprising of one PC mix was the control for the experiment, and 18 different mixes of Kenaf bio fibrous concrete composite (KBFCC) at varying fibre volume fraction (vf) and fibre length (lf) were tested. These mixes were tested for workability (slump, compacting factor and Vebe test) and fresh density. The slump and Vebe time for KBFCCs were 5–100 mm and 3–79 seconds respectively. The slump and Vebe time for PC were 120 mm and 3 seconds respectively. A significant drop from 0.951 to 0.809 for fibre length of 25 mm, 0.947 to 0.799 for fibre length of 50 mm and 0.931 to 0.793 for fibre length of 75 mm was observed for the compacting factor value. Though, KBFCC with fibre content below 1% was workable in spite of its low slump, its high Vebe time and low compacting factor. For fibre volume of 1% and above, the workability of concrete decreased and became very stiff with balling effect. It was seen that fresh density of PC concrete (2358 kg/m3) was higher compared to those of KBFCC (2105-2339 kg/m3), however, both values were lower than 2400 kg/m3 threshold specified by the BS code of practice. The study therefore recommended that fibre contents lesser than 1% and 50 mm length can be used in order to have good fresh properties performance.