INTERNODAL AND ECO-SPATIAL VARIABILITY OF SELECTED PHYSICAL AND MECHANICAL PROPERTIES OF GLULAM Bambusa vulgaris SCHRAD. EXJ. C. WENDI IN NIGERIA

Abstract

Utilisation of bamboo as substitute for wood is being recognised globally as a result of declining availability of timber species. Bamboo’s surface curvature and thickness are major challenges to its potential and thus, glulam technology is being adopted to improve bamboo’s surface and thickness. However, internodal and eco-spatial variations in bamboo properties affect application of glulam technology for its various uses. Knowledge of technical properties of Bambusa vulgarisglulam from different internodes and ecosystem is limited. Therefore, technical properties of B. vulgarisglulam at different internodes from three ecological zones of Nigeria were investigated. Three ecological zones: Mangrove Swamp Forest (MSF), Lowland Rain Forest (LRF) and Guinea Savanna (GS), were purposively selected based on geographical distribution of bamboo. In each zone, 20 five-year old bamboo culms were randomly selected. Along each culm, ten sampling points (SP1 ̶ lowest basal point to SP10 ̶ topmost point) at 3 - internodes intervals were systematically selected from base to top for glulam boards production. Physical properties [density (D, Kg/m3), volumetric shrinkage (VS%)] and mechanical properties [Modulus of Rupture (MOR, N/mm2), Modulus of Elasticity (MOE, N/mm2), Maximum Compressive Strength Parallel to Grain (MCS//, N/mm2) Maximum Compressive Strength Perpendicular to Grain(MCS ḻ, N/mm2) and Shear Strength (SS, N/mm2)] of glulam boards were determined using standard procedures. Data were analysed using descriptive statistics, ANOVA and correlation analysis at α0.05. The density significantly increased from 0.32±0.01 to 0.64±0.00 while the volumetric shrinkage decreased from 9.47±0.00 to 7.74±0.00 in SP1 and SP10, respectively. The MOR and the MOE were 531.55±0.01; 6535.60±0.05 and 702.45±0.19; 9840.00±0.67 in SP1 and SP10, respectively. The least and the highest MCS// (16.00±0.08; 26.90±0.03) and MCSḻ (3.34±0.00; 7.51±0.03) were recorded in SP1 and SP10, respectively while the SS varied from 2.46±0.01, to 7.51±0.03 in SP1 and SP10. The density ranged from 0.47±0.07 (MSF) and 0.58±0.006 (GS) while the VS were 7.96±0.16 and 9.22±0.21 in GS and MSF, respectively. The least and the highest MOR and MOE were 543.68±11.04; 600.64±53.42 and 7883.22±909.71; 9090±653.41 in MSF and GS, respectively. The MCS//, MCSḻ and SS were 18.52±1.89 and 22.91±2.81; 5.14±0.87 and 6.09±0.53; 4.33±1.21 and 5.96±1.09 in MSF and GS, respectively. The volumetric shrinkage significantly correlated inversely with density across the ecological zones with r value of -0.94 (MSF); -0.98 (LRF); -0.92 (GS). The MOR and MOE were positively correlated with the density with r values of 0.91; 0.96; 0.82 and0.99; 0.98; 0.99 in MSF, LRF and GS, respectively. The MCS//, MCSḻ and SS had significant positive correlation with density with r values of 0.94; 0.97; 0.93, 0.98; 0.99; 0.99 and 0.98; 0.99; 0.93 in MSF, LRF and GS, respectively. The physical and mechanical properties of glulam boards of Bambusa vulgaris progressively improved in quality from the basal to the topmost internodes. The glulam boards of Bambusa vulgaris from the Guinea Savanna had the best mechanical and physical properties than those from other ecological zones.