Modulus of Rupture
Modulus of rupture (MOR) strength is an important characteristics when the products are used as panels, e.g. in ceiling and roofing. Except for untreated wood (control) all the specimens tested for MOR in this experiment exceeded the requirements (1.27 N/mm2) of the specification of the British Standard (BS/1105, 1972). Results of the analysis of variance showed that the effect of extraction and the interaction term (extraction*calcium chloride) were significant. The coefficient of determination (R2) was 0.94 1, which means that 94.1% of the variation in MOR could be explained by the main factors and their interaction. In the same percent of calcium chloride, there was a significant difference between the extracted and unextracted wood; however, there were no significant differences between the means of the two levels of extracted wood for 7 and 14 days. These results agree with the findings of Gnannaharan and Dhamodaran (1985) that cold water extraction removes the inhibitory extractives from tropical species.
Hardness strength test is required if the products are used in flooring or paving or as bearing blocks. Hardness values in this experiment ranged from 200 to 9200 N with an overall mean = 5022 N. Results of the analysis of variance showed that the effect of extraction and the interaction term were significant, which indicate that the effect of the factors are on each other . At all levels of calcium chloride, there were significant differences between the extracted and nonextracted wood mixture. Only at 1% calcium chloride, there were significant differences among the three levels of extraction .In control (unextracted wood) there was a significant decrease in hardness means with increased calcium chloride percent. When the wood was extracted for 7 days, hardness strength showed an increase with increased calcium chloride. However, there were no significant differences between 1.5% up to 3.5% levels and also no significant differences between 1, 3 and 3.5% calcium chloride. Wood extracted for 14 days showed that the hardness of the specimens with 1 and 1.5% calcium chloride were significantly lower than the specimens with 2, 2.5 and 3% but not different from that with 3.5% calcium chloride. From the above results it can be concluded that the amount of calcium chloride to be added to the sunt wood-cement mixture should be 1%, 1.5% and 2% for the unextracted (control), 7-days extracted and 14-days extracted wood, respectively.
Water absorption is important when the products are used externally (out door).
Tests for water absorption were done for 2 and 24 hours.
Water absorption for 2 hours
About 94% of the water was absorbed in the first 2 hours of soaking. Results of the analysis of variance shows that the effect of the two main factors (extraction and calcium chloride) and their interaction term were significant. At the same calcium chloride percent, unextracted wood (control) absorbed significantly higher amount of water than the extracted wood, except in 1% calcium chloride there was no significant difference among the three levels of extraction. This may be due to different setting of wood-cement; more porous of the non-extracted wood mixture compared to the extracted wood mixture, caused more water absorption. When the wood was extracted for 7 days, there were no significant differences in 2 hours water absorption among all added calcium chloride percentages. If the wood was extracted for 14 days, then increasing the calcium chloride percent led to a decrease in the 2- hours water absorption. So, there were no significant differences between the calcium chloride percents from 1 to 2.5 and from2.5to 3.5. The values of the means of the various treatments combinations ranged from 44.3 to 63.2%.
Water absorption for 24 hours
Soaking the specimens in water for 24 hours increased the amount of absorbed water by an average 6% compared to soaking for 2 hours. At all calcium chloride percentages, except 1%, there was a significant difference between extracted and unextracted wood. When the wood was extracted, there were no significant differences in water absorption among all percentages of added calcium chloride. Water absorption for 24 hours had values ranging from 43 to 67% with an overall mean equal to 52%.
For external uses, dimension swelling was important. Results of the analysis of variance showed that the effect of the two main factors (extraction and calcium chloride) and the interaction term were not significant on the dimension swelling. That is to say that the extraction and the calcium chloride did not influence the thickness, width and the length swelling. The tested specimens showed high stability in dimensions with the overall mean equal to 1.28, 0.78 and 0.98% for thickness, width and length swelling, respectively. This was less than the thickness swelling in Bisons, but less or equal to the 2-hours and equal to or more than the 24-hours swelling in Duripanel results.