INTRODUCTION Bamboo, a plant with hundred of uses has long been associated with short life span products. Mankind has long exploited bamboos, like other lignocellulosic materials, for various purposes and reasons (Tewari & Bindhi Singh, 1979). They are used intensively for making a wide range of products such as house-hold items, handicrafts, paper, joss-sticks, barbecue sticks and chopsticks. It is one of the oldest light building materials used in the rural areas and villages due to its availability, low cost, strength, and high yield and renewable nature.
Bamboos considered to have a very low natural durability, when placed in contact with soil (Liese 1985, Kumar et al. 1994, Jayanetti & Follett, 1998), the young bamboo culms in particular or that has been insufficiently treated with preservatives usually deteriorate rapidly by the action of a mixed population of soil microorganisms and termites. Fungi and termites may still colonize even to those bamboo regarded as adequately treated with preservative. The decay and the attack rates on these bamboo may be slower, and the patterns of fungal colonization may also differ from untreated or less adequately treated bamboo.
Trials on the present study on the in-ground performance of bamboo treated with preservatives were started from 1995 to 1997. The aims of these study were to determine and assess the durability between untreated and chemically treated bamboo against fungal and termites attacked in short term ground contact tests. Information generated from the study will help to promote and increase the utilization of bamboo for construction and exterior uses. MATERIALS AND METHODS The bamboo samples for this study were taken from the Forest Research Institute of Malaysia’s (FRIM) research trial plot in Nami, Kedah in Malaysia.
Bamboo culms were cut at about 30 cm above the ground level. These culms of known age were taken from randomly selected clumps all had diameters between 8 to 10 cm. They were harvested in the months of February 1995 immediately after the rainy season. Investigations indicated that bamboo harvested during this period contained a very minimum amount of starch (Sulthoni, 1983; Liese, 1985; Abd. Razak et al. , 1995). The top parts of the culms with branches were removed leaving bamboo poles of about 12 metres in length.
All together 400 bamboo poles consisting of 200 of the two-year and another 200 of four-year old were harvested. These poles were later subdivided into 3 equal lengths consisting of bottom, middle and top portions of 4 meters each. These were later treated with ACQ Type B (CuO 60. 7%, DDAC 33. 3%) and CCA Type C (CuO 18. 5%, CrO3 47. 5%, As2O5) through soaking, vacuum impregnating and high pressure sap-displacement processes. These blocks were converted into 500 mm x 20 mm x culm wall thickness and were chosen from the bottom, middle and top portion of the culms.
This test were conducted based on ASTM: D 1758-74 (Anon, 1974) and procedure developed by Jackson (1957), but with some modification. The total numbers of test stakes investigated were 900 consisting of 2 age-group, 3 culm-height, 3 type of treatments, 3 type of preservatives, 4 level of preservatives and 4 replication. The test stakes were buried upright with 4/5 of their length in the ground. They were installed 200 mm apart within and between rows and were distributed randomly based on randomized complete-block design. The test stakes were exposed to the decay hazard as well as termites.
The tests were monitored for a period of 24 months from July 1995 to June 1997. The stakes were installed during the dry season. The testing site for the field/grave-yard study was located in Melaka, Malaysia. The site is located in a lowland area. The site is in an agriculture land having hot and humid climate throughout the year with an average daily temperature vary from 21? to 32? C and average rainfall of about 2540 mm. DISCUSSION The greater exposure effect after 24 months period of the field stakes trial is seen in the decay ratings.
The stakes site used was found to have a relatively low level of termite activity (this is clearly seen in Table 3). The assessment of the untreated control stakes shows that these stakes lasted less than 2 years. A similar observations were also made by Purushotham et al. , 1953 and Kumar et al. , 1994. Comparison between the three methods used in the study clearly shows that vacuum treated stakes performed better than soaking and high pressure sap-displacement treated stakes in area such as age of stakes, types of preservatives used, concentration of preservatives and height of the culms from where the stakes were taken.
This can be seen in Table 12 for the comparison of the means. The decay and termites rating in the 4 year-old bamboo treated stakes were found to be slightly higher compared with those of the 2 year-old stakes. This might be due to the fact that the 2 year-old stakes possess higher preservatives retentions compared to the 4 year-old stakes (Razak, 1998). Age of bamboo culm The culm age of bamboo to a certain extent played an important role in determining their durability in field environment.
This element is not considered to be a major factor compared with, for example, preservative type or concentration. However, a small and statistically significant increase in durability of untreated or treated 4 year-old stakes was found (see Tables 4, 7, 11 and 12). Treatment technique The treatment technique proved not to be the critical factor in influencing the good performance of the bamboo tests stakes. Figures 1 to 10 show the rating of the stakes by various treatment techniques employed in the study.
As clearly seen from the figures the rating of decay and termites attack does not depends on the treatment methods employed. The rating assessment more or less shows some consistency that does not differ much between the soaking, vacuum pressure and high-pressure sap-displacement process. However, some variations do occur depending on the net dry salt retention (NDSR) uptakes between the various treatment techniques applied to the tested stakes. But when the factor of costing is taken into consideration the soaking treatment may have an advantage.
Vacuum pressure treatment is quite expensive to be employed commercially in the bamboo industry. High pressure sap-displacement treatment proved to be time consuming as relatively few bamboo culms can be treated at one particular time. And only round bamboo can be treated by this method. This technique proved to be uneconomic for commercial usage in treating bamboo. Preservatives The type of preservatives used influenced greatly the outcome of the study. CCA treated stakes apparently and consistently gives better performance than the ACQ treated stakes.
The rating for ACQ treated stakes were close next to CCA. It is also clear that on an average, the CCA preservatives proved to be more effective against fungal attack compared with ACQ. Strength /Concentration of preservatives solution The higher retention in the treated bamboo stakes when treated at higher concentration of preservatives such at 4% and 8% level were still performing well after 24 months in the field trial. Even 2% solution strength with CCA and ACQ were giving good performance, as was CCA at a 1% treating solution concentration