Shrinkage Properties of Kenaf Bio Fibrous Concrete Composite for Sustainable Construction.

Abstract

An experimental study had been carried out to investigate the fresh and shrinkage properties of kenaf bio fibrous concrete composite (KBFCC). A short discontinuous natural fibre commonly called kenaf fibre was used in the mix production as against the commonly used steel or synthetic fibre. The fresh property investigated in this study is concrete workability, which was tested using the slum, VB and compacting factor. Eighteen different fibrous concrete mix proportions and one plain concrete mix (control) were cast. The volume fraction, Vf for the fibrous concrete was a varying percentage between 0.25% to 2% at an interval of 0.25% and a fibre length at 25 mm, 50 mm and 75 mm. The concrete strength was designed to achieve grade C30 at 28 days. The results revealed that the inclusion of bio fibres in concrete decreased the workability of concrete due to its hydrophilic nature and affinity for water. It was observed that the concrete containing 50 mm fibre length and fibre volume of 5% gives the most appropriate combination as regards to the workability of the concrete. KBFCC demonstrated substantially lesser shrinkages compared to plain concrete specimens. The lowest shrinkage strain was recorded for 50 mm Kenaf fibre length mixture containing fibre below 1% tested at 28 days hydration period. It was also observed that Kenaf fibres become more active in restraining free drying shrinkage of concrete as the age of drying increases. The reduced shrinkage of the KBFCC when compared to PC can be attributed to the moisture holding capacity of kenaf fibres and the presence of randomly oriented fibres around the cement gel which create a condition of confinement inhibiting the shrinkage development of concrete.