(L) Seeds on Germination of Striga Hermonthica (Del.) Benth Seeds

JOURNAL OF FOREST PRODUCTS & INDUSTRIES, 2013, 2(4), 16-21 ISSN:2325–4513(PRINT) ISSN 2325 - 453X (ONLINE)19The results of the mean separation test for the effect of differentwood pretreatments on compressive strength (Kg/cm 2 ) showedthat addition of gypsum gave the highest value and wassignificantly different from all other treatments followed bycontrol, addition of calcium chloride and soaking in cold water,between which no differences were found. Extraction by NaOH1% was ranked last, and this may be attributed to the adverseeffect of the sodium in lowering the air dry density, in this studyincreasing density associated with better properties and this isgoes in total agreement with the finding of abdalgadir andIbrahim [2] who stated that the compressive strength is highlycorrelated with the density of wood cement mixture. Previousworks of Hassan [17] and Ibrahim [18] concluded that, additionof calcium Chloride help in improving the compressive strengthand ranked first, while in this study addition of calcium chlorideranked secondly. Addition of gypsum (20% -based on cementweight) increased the compressive strength more than 100%compared with the others treatments and displaced calciumchloride from the top rank. This may possibly be due toincreased air dry density. An exciting result was that soakingmesquite wood in cold water as well as control shared the samerank with addition of calcium chloride, which indicated thatmesquite wood can safely be used to produce cement bondedproducts without any sort of treatment. This may be attributed tothe fact that the extractives present in mesquite wood did nothave an inhibitory effect on cement setting.As shown in Table 2 the results of the mean separation test forthe effect of wood pretreatment on the water absorptionpercentage of mesquite wood – cement bonded aggregates.,addition of gypsum, addition of calcium chloride and controlsgave the best result when soaked for two hours and were notsignificantly different from each other, but were significantlydifferent from soaking in cold water and soaking in 1% sodiumhydroxide solution (Table 2). But when soaking was extendedto 24 hours, addition of gypsum and addition of calciumchloride significantly improved water absorption, while controlranked third, but not significantly different from addition ofcalcium chloride. Soaking in 1% sodium hydroxide solutionopposite was true. The results of mean separation test for theeffect of cement/ wood ratio on water absorption are shown in 7revealed that, significant differences between the ratios wereobserved when the specimens were soaked for 2 hours, with thetrend that as cement wood ratio increased water absorptiondecreased. This result goes in total agreement with the findingof Elten [21] who found that the water absorption tended todecrease as the amount of cement was increased from 50:50 to30:70. Obviously, a higher wood content (lower cement: wood:ratio), would result in greater water absorption due the nature ofwood which will be less surrounded by cement, but increasingthe cement ratio results in better coating of wood particles. Thisprevents them from absorbing water. There were alsosignificant differences between ratios when specimens weresoaked for 24 hours, which indicate that the aggregatesshowed the highest percentage of water absorption. Generallypretreating any hardwood improves water absorptionpercentage due to improvement of cement setting conditions.Previous work by Hassan [17] and Ashraf and abdalazim [5]concluded that the addition of calcium chloride significantlyimproved water absorption percentage. However addition ofgypsum in this study showed better aggregate performance thanaddition of calcium chloride.Effect of cement/wood ratios on the density of mesquitewood/cement bonded aggregatesMean separation test results for the effect of cement wood ratioon mesquite wood-cement bonded aggregates air dry density,compressive strength and water absorption percentage (2 and 24hours) were presented in Table 3. Regarding air dry density, nosignificant differences were observed between ratios 4:1 and5:1which gave the highest value. But there were significantdifferences between the other ratios. As expected increasingcement/wood ratio results in increased aggregate air dry densitysince addition of more cement means increasing the specimenweight. The same conclusion was found by Zhou and Kamdem[19] who stated that, cement-bonded particleboard that utilizelarge amounts of cement in comparison to wood (cement: woodratio higher than 3:1), result in final product with high density(>1300 kg/m 3 ), because cement is denser than wood. AlsoOyagade et al., [20] reported that veneer laminatedcement-bonded particleboard were stronger and stiffer withincreased cement/wood ratio due to increased density.As shown in Table 3 significant differences were foundbetween the four studied ratios regarding compressive strength.As observed from the Table 3 increasing cement: wood ratioresulted in increasing compressive strength. This can beattributed to the increased air dry density. This goes in totalagreement with the finding of Abdelgadir and Ibrahim [2] whoconcluded that compressive strength of cement- wood mixturefor five Sudanese hardwood species is considerably reduced ascement/wood ratios were decreased and theabsorbed huge amount of water during the first hours of soaking,while increasing the soaking time result in only a fewpercentages of increase (3-6%). which agreed well with theconclusion of Hassan [17] who concluded that soaking in waterfor 24 hours increased the amount of water absorption by anaverage of 6% compared to soaking for 2 hours. From all abovementioned results, it may be concluded that aggregates with lowcement wood ratio absorb more water and possesses lowercompressive strength. However, aggregates with highercement/wood ratio (4:1 and 5:1) absorb small amount of water,possesses higher compressive strength and heavy weight (highdensity). The aggregate produced with cement wood ratio of 3:1had reasonable weight, good strength and reliable density. Theoverall conclusion is that 3:1 cement wood ratio is the suitableand recommended ratio to be used for untreated mesquite wood.