COMPARATIVE STUDIES ON SELECTED PROPERTIES OF CEMENT BONDED COMPOSITES PRODUCED FROM GLIRICIDIA SEPIUM, TERMINALIA SUPERBA AND GMELINA ARBOREA

Abstract

This study was conducted to evaluate and compare the properties of cement bonded composites boards made from sawdust of Gliricidia sepium, Terminalia superba and Gmelina arborea. A high proportion of waste is generated through the process of conversion of logs into planks in sawmill, these wastes have been utilized over the years for the production of cement bonded composites product. This project will help in reducing environmental pollution related to disposal of wastes. The replacement of asbestos and urea formaldehyde boards with CBC made from wood residues and cement result in an environmental friendly substance. The use of less valuable wood species (Gliricidia sepium) for the production of panel products as alternatives to sawn timber will increase the industrial and economic base on the national development. The suitability of Gliricidia sepium, Terminalia superba and Gmelina arborea sawdust for the production of cement bonded composites product was examined. The influence of board densities, cement wood ratio and the effect of accelerated aging on some selected physical properties of the composites board produced was also examined. The Board formation was based on cement:wood ratios 1:1, 2:1 and 3:1, board densities of 800, 900 and 1000 kg/m3 by dry weight. The quantity of cement, particles, and water for each board was weighed, mixed separately and very well in order to prevent the formation of particles lumps. Blended mixture was transferred and formed to the mould of 650 mm x 650 mm x 13 mm covered with polythene sheet (to prevent sticking of the mixture) before a plywood was laid at the top of the mat. The mat formed was pre-pressed and the mould was placed in between top and base caul plates and pressed with the aid of hydraulic jack. After 24 hours, the board was removed from the mould and cured in sealed polythene bags, after which it was conditioned under stack for 28 days. The boards produced were trimmed to sizes and test samples for evaluation were cut into various samples sizes for laboratory investigation. The board properties evaluated were water absorption, thickness swelling, accelerated water absorption, accelerated thickness swelling, modulus of rupture and modulus of elasticity. For the boards produced from Gliricidia sepium cement bonded composite board, mean value for water absorption and thickness swelling ranged from 3.06 to 6.99 % and 1.40 to 7.51 %, respectively. Mean value for water absorption and thickness swelling ranged from 1.85 to 6.31 % and 0.85 to 6.28 %, respectively for Terminalia superba cement bonded composite board. Gmelina arborea cement bonded composite board mean value for Water absorption and thickness swelling ranged from 2.94 to 6.66 % and 1.08 to 7.48 %, respectively. Following accelerated aging test, Gliricidia sepium cement bonded composite board mean value for water absorption and thickness swelling ranged from 3.41 to 8.12 % and 3.46 to 15.58 %, respectively. Mean value for water absorption and thickness swelling ranged from 1.96 to 6.83 % and 0.84 to 13.68 %, respectively for Terminalia superba cement bonded composite board. Gmelina arborea cement bonded composite board mean value for Water absorption and thickness swelling ranged from 3.08 to 7.47 % and 1.84 to 15.29 %, respectively. The Modulus of rupture (MOR) mean values ranged from 0.76 to 10.22 N/mm2 for Gliricidia sepium, 1.00 to 18.39 N/mm2 for Terminalia superba and 0.83 to 12.23 N/mm2 for Gmelina arborea, for the cement:wood ratios at different levels of density. Mean values of Modulus of Elasticity (MOE) of the experimental boards produced ranged from 180.77 to 405.83 N/mm2 for Gliricidia sepium, 187.99 to 832.88 N/mm2 for Terminalia superba and 195.56 to 619.43 N/mm2 for Gmelina arborea, for cement:wood ratios at different levels of density. Water absorption and thickness swelling decreased with increase in board density and cement:wood ratio. Following accelerated aging test, water absorption and thickness swelling decreased with increase in board density and cement:wood ratio. Modulus of rupture and modulus of elasticity increased with increase in board density and cement:wood ratio. All the boards produced from cement:wood ratio 3:1 and board density of 1000 kg/m3 from three wood species were more suitable for the production of cement bonded composite board due to improved physical and mechanical properties. Increase in board density and cement:wood ratio accounted for the production of more dimensionally stable composite boards. Terminalia superba cement bonded board gave the best physical and mechanical properties compared with Gliricidia sepium and Gmelina arborea cement bonded composites board.