In a cement board (CB) composite, fibres reinforce the board. It is because the length of the fibres significantly impacts the strength of the CB composite. Nonetheless, the physical properties of the CB are also an important aspect when dealing with the quality control of the final product. This study investigates the effects of various fibre lengths in CB fabrication on its physical properties, including the cement-hydration rate, tensile strength, density stability and thickness swelling (TS). Oil palm empty fruit bunch (OPEFB) fibres at different lengths are used based on the mesh retained size of R7M, R14M, and R30M. The OPEFB-CB mixture used in this research is 3:1 (cement: fibre ratio), with a target density of 1,300 kg/m³. The sample is compressed using a 1000 psi cold-compression load to achieve the desired composite thickness of 12 mm. This research revealed that the longest fibres retained on the R7M mesh with an average length of 5 mm resulted in lower density and the highest TS value. Meanwhile, lower dimensional stability was achieved by OPEFB-CB composites using fibre that retained on the R14M and R30M, having an average length of 3 mm and 1 mm, respectively. Based on the results, the optimum fibre length recommended in the fabrication of OPEFB-CB composites is processed fibres retained on the R14M sieve with an average length of 3 mm. This recommendation is made based on the most stable density and lowest TS results achieved by the R14M retained fibres which is in the range of 1,231–1,309.4 kg/m³ and TS of 0.65 %.

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