Strength development and crack pattern of coconut fibre reinforced concrete (CFRC)

Abstract

Concrete fails suddenly under tension and cracks excessively when unreinforced. Steel rebar is conventionally used to reinforce concrete. However, it is expensive to many people in most developing countries. In tropical regions, natural fibres are abundantly available which when utilized will reduce cost of construction and improve performance.This paper focuses on the use of coconut fibres as reinforcement in concrete. Coconut fibres were extracted from coconut seeds and chopped into 40 mm in length. Concrete of mix ratio 1:2:4 was produced which contains coconut fibre of 1, 2, 3 and 4% by weight of cement.  Compressive strength and modulus of rupture of CFRC specimens were determined following standard procedures at curing ages of 7, 21, 28 and 56 days. Also, crack pattern was monitored. The results showed that the water-cement ratio increased from 0.62 to 0.70 as coconut fibres (CF) increased from 0 to 4%, while the compressive strength only increased up to 2% CF but dropped afterwards when compared with normal concrete (NC). At 28-day, flexural strength of CFRC were 2.73, 2.79, 2.88 and 3.01  at 1, 2, 3, and 4% CF content representing 107.5, 109.8, 113.4 and 118.5% of NC. There was gradual tensile failure in CFRC with minor to hair-like crack as compared to sudden failure with wide crack from tension zone to compression zone in NC. The study concluded that up to 2% content of CF is recommended for concrete reinforcement.