Behaviour of natural fibre reinforced concrete composite under impact loadings

Abstract

Natural fibres are environmentally-friendly, economical, lightweight, renewable, and have excellent thermal and acoustic insulating properties. Although the history of the applications of natural fibres in civil construction goes back thousands of years, few studies have been conducted to investigate the behaviour of natural fibre reinforced concrete composites until recent decades, especially in regard to impact loads. This research aims to study the impact behaviour of a natural fibre reinforced concrete composite. Flax fibre reinforced polymer strengthened coconut fibre reinforced concrete (FFRP-CFRC) was first developed at the University of Auckland. To study its impact behaviour, experiments were carried out on various types of specimens, i.e. FFRP laminates, CFRC cylinders, FFRP-CFRC beams and slabs. Initially, the impact behaviour of FFRP laminates was studied using both an instrumented drop weight machine and a Charpy testing machine. The dynamic tensile properties of FFRP under various strain rates were studied using a high-speed servo-hydraulic machine. Then, to study the effect of coconut fibre length, single and repeated drop weight impacts were carried out on CFRC cylinders. Impact loads were also applied to FFRP wrapped CFRC beams to investigate the influence of coconut fibre content on composites behaviour. The results indicated that 3% of coconut fibre content in specimens was best in resisting impact compared with 1% and 5% specimens. Furthermore, the effect of FFRP thickness (2-, 4- and 6-layers) on impact behaviour of FFRP laminated CFRC beams was also studied. In addition, impact experiments were conducted to compare CFRC slabs with three different FFRP wrapping configurations. A theoretical model was applied to predict the maximum impact force and maximum deflection. The last experiment was a study on FFRP renovated cracked CFRC slabs with two configurations. The outcomes of this research will contribute to a comprehensive understanding of the impact characterization of FFRP-CFRC composite, which is helpful in designing impact resistant natural fibre reinforced concrete composites. It also provides an assessment of this FFRP-CFRC material for construction or retrofitting residential buildings.