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An appraisal of methods for environmental testing of leachates from salt-treated wood; part 1
1998 - IRG/WP 98-50115
The magnitude and diversity of leaching tests with salt-treated wood, performed by institutes as well as industry, strongly appeal for harmonisation towards one single method. That procedure should be well-defined, cost- and time-effective and moreover be extended with a clear detection and interpretation scheme. The paper(s) presented here tend to evaluate 2 existing leaching methods, the ENV 1250.2 and the EN 84, for their potential use as an environmental standard in high hazard class wood preservation. The leachates obtained are chemically examined for their patterns and levels of metal emission and are biologically screened for their releavance towards in service biomonitored samples. Upon strengthening the objectives and characteristics of the EN 84 ageing test, the results reported here justify the support and upgrading of this procedure as an early stage leaching method within the standard efficacy testing of new or renewed wood preservatives.
G M F Van Eetvelde, M Stevens, F Mahieu, H-W Wegen, A Platen
The biological effectiveness of wood modified with heptadecenylsuccinic anhydride against two brown rot fungi: Coniophora puteana and Gloeophyllum trabeum
1992 - IRG/WP 92-3705
A modified soil block test was carried out using wood samples reacted with heptadecenylsuccinic anhydride (ASA). This modification gave good resistance to decay brought about by the brown rot fungi Coniophora puteana and Gloeophyllum trabeum during the twelve week exposure period. Results indicated that there was a good correlation between increased loading of modifying reagent and an increase in effectiveness paralleled by a marked reduction in wood moisture content. The effective resistance threshold level was calculated to be about 30% weight gain of ASA. Further discussions regarding the mode of action are included.
C Codd, W B Banks, J A Cornfield, G R Williams
Methods for Studying Penetration Depth of Wood Protection Products
2010 - IRG/WP 10-20432
EN 152 is an accepted standard in Europe for measuring how deep a wood protection product penetrates into the surface of treated pine wood. The method has provided consumers with a wide assortment of products that meet the specifications outlined in the standard. Because the test takes 8 or more months to carry out, artificial ageing procedures have evolved in order to standardize and speed up the procedure. Small changes in a formulation will often change a products physical parameters and especially its ability to penetrate into wood. It is therefore desirable to develop a method that can measure changes in a product’s penetrability quickly and accurately. A method is described where wood cores are drilled from treated wood, then sliced in 100 µm thick discs. Discs are then placed on nutrient agar plates seeded with conidia from Aspergillus niger. Plates are incubated for 24 hours and zones of inhibition are measured. It is believed that if a fungus is growing on the disc the biocide level will not exceed that of the fungus minimum inhibition concentration (MIC). In water based acrylic systems penetration depths are often less than one mm and it can impact the performance of a product if that changes. The procedure described in this study can show if penetration of a preservative product has been increased or reduced in as little as 24 hours.
K Hansen, L Sites, D D Nicholas
Utility, deterioration and preservation of marine timbers in India
2005 - IRG/WP 05-40314
Timber is extensively used in India in the marine environment for various purposes due to its several advantages over modern materials. Infact, its use is increasing in recent years, finding wider and wider applications and this scenario is not going to change in the near future. Though, the bio-deterioration problem is found very severe in tropical waters, still indigenous methods are widely employed for the protection of fishing craft and the present level of chemical treatment is well below 5% of total timber used. This is due to socio economic problems of the potential timber user groups, unavailability of treatment plants in the coastal areas, lack of awareness in user groups, etc. In this paper, types of fishing craft used in the country, timber uses in the marine environment, bio-deterioration losses, research conducted on bio-deterioration aspects at various places and methods applied for the protection of wooden structures are presented.
B Tarakanadha, M V Rao, M Balaji, P K Aggarwal, K S Rao
Wood preservation in Kenya
2000 - IRG/WP 00-40191
Current research on wood preservation in Kenya is mainly on the development of biological control of wood-destroying termite species, using mycoinsecticides. The major research institutions include the Kenya Agricultural Research Institute (KARI), Kenya Forestry Research Institute (KEFRI), Moi University and the International Centre for Insect Physiology (ICIPE). Training institutions include Forestry Training College, Forest Products Training Institute and Moi University. A number of publications, mostly an biological control of termites, are available and they range from workshop and conference proceedings to theses and journal publications. Wood-destroying termite species include several genera in Macrotermitidae and one drywood termite genus. Wood preservation facilities are available in Kenya, mainly for assorted timber products, sleepers and utility poles. The major preservatives used are CCAs, PCP and Creosote oil. There are still no set standards, specifications and requirements for wood preservatives and little, if any information exists on the marketing aspects of wood preservatives. The yet to be established Industrial Chemicals Act and the recently introduced Environmental Management and Coordination Bill (1999) may be able to handle regulatory, environmental, health and safety aspects of wood preservation in Kenya.
Evaluating the natural durability of a number of lesser known species of Ghanaian hardwoods using a short term laboratory assay
2004 - IRG/WP 04-10540
Resistance of a number of Ghanaian hardwoods to attack by the crustacean Limnoria quadripunctata was assessed by measuring the production of faecal pellets under forced feeding conditions over a two week period. Small sticks of commercially available, lesser known timber species, were leached in seawater for one week then placed in a cell culture chamber with one animal and 4 ml of seawater. At intervals, the number of faecal pellets per chamber was counted. The number of pellets produced by animals feeding on Scots pine sapwood, which is non-durable, and on greeheart or ekki, timbers with a reputation for resistance to marine borer attack, were used as a basis for comparison. Mortality rates were also compared. Lower pellet production rates and higher mortality rates were taken as measures of natural durability. Feeding on ekki (Lophira alata), kusia (Nauclea trillesii) and ananta (Cynometra ananta) was about one tenth of that on Scots pine. Mortality of animals with wonton (Morus mesozygia) was 90%, but high mortality did not occur with any of the other species.
J R Williams, S M Cragg, L M S Borges, B Shayler
Preliminary screening of diffusion formulations for the control of soft rot
1978 - IRG/WP 2104
We have an urgent need in Australia to develop in situ remedial treatments for the present population of in-service transmission poles. For various reasons we have opted for formulations which can be applied as bandage treatments and thus we are primarily concerned with assaying diffusable toxicants. Two basic approaches have been made: an assay of the formulation's toxicity; and a combination assay of the formulation's diffusibility and toxicity. Of the direct assay methods the filter-paper technique is the more rapid although with highly soluble formulations some leaching of toxicants will occur during the preparatory stages and probably during incubation also. Furthermore, filter papers are not strictly comparable to wood, and a modification we have considered is to use 'papers' prepared from mechanically beaten pulps rather than chemically degraded pulps. An additional modification would be to substitute veneers for filter papers, although this may give rise to surface concentration effects since the veneers could prove difficult to impregnate homogeneously. By far the most valuable technique for our own screening programme of potential toxicants to control soft rot in standing poles is the Petri dish/wood slab technique. While agar diffusion systems are rapid and provide valuable 'short list' data, the information obtained on diffusion rates cannot easily be applied to solid wood. Da Costa's slab technique is obviously advantageous in this respect. Furthermore, it can be so tailored that successive inocula can be sequentially assessed, thereby providing added information on component diffusion as well as total formulation movement. However, care must be taken in interpreting the data since it is not possible to distinguish directly which chemicals in a mult-component formulation have diffused first and hence which are the toxic ones. Similarly, it could be necessary to impose a time restriction on the test with certain types of formulations.
Towards a colour assay of wood degradation
1982 - IRG/WP 2180
A colour assay for the enzyme catalase is described. Since the activity of this enzyme has previously been shown to be correlated with degree of wood degradation as determined by other methods, this assay may provide a rapid quantitative indicator of superficial and internal wood decay.
M A Line
A behavioral assay for measuring feeding deterrency of a slow-acting biocide, A-9248, against the Formosan subterranean termite (Isoptera: Rhinotermitidae)
1988 - IRG/WP 1366
Concentration-dependent feeding deterrency of a slow-acting compound, A-9248 (diiodomethyl para-tolyl sulfone) was studied in a choice test against the Formosan subterranean termite, Coptotermes formosanus Shiraki. A-9248 was a feeding deterrent at concentrations ³8,000 ppm. Initially, Coptotermes formosanus fed on wood treated with 1,000-6,000 ppm A-9248 but learned to avoid the treatment as a result of ingesting sublethal doses of A-9248. Only those groups exposed to wood treated with <1,000 ppm continued feeding on the treated substrates, and ingestion of these concentrations resulted in 85-100% mortality at the end of the 4-week experiment.
N-Y Su, R H Scheffrahn
A rapid colorimetric assay for mold spore germination using XTT tetrazolium salt
2011 - IRG/WP 11-20462
A rapid colorimetric assay was developed to quantitate metabolic activity in mold spores during germination using 2,3-Bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[9phenyl-amino)carbonyl]-2H-tetrazolium hydroxide (XTT). The assay was used to demonstrate inhibition of spore germination following exposure to different biocides and variability in the inhibition of spore germination of different mold species to the same biocide.
C A Clausen, V W Yang
ATP assay for the determination of mould activity on wood at different moisture conditions
1992 - IRG/WP 92-2397
To determine fungal responses to fungicides and environmental conditions and for detection of microbial activity in wood, sensitive and objective methods are needed. We have developed a suitable assay based on analysis of adenosine triphosphate (ATP) by using the luciferin-luciferase reaction. With the aid of this assay the activity of Penicillium brevicompactum on wood at different RH levels was studied. The ATP content in a two week old culture responded quite rapidly to changes in humidity. The ATP content in the colony moved to 70% or lower RH for one week was 10 times lower than the ATP content in the colony kept at 100% relative humidity for the same time period. Increasing the humidity level to 100% RH one week before the ATP determination from a period at lower humidities did not result in a significant increase in the ATP content. This probably indicates that the mycelia of the fungus did not survive the low humidity treatment.
Oxalic acid quantification, oxaloacetase assay and ESI localization of P, C, and Fe from the brown rot fungus Postia placenta
1994 - IRG/WP 94-10063
The mechanism by which brown-rot fungi initiate depolymerization of holocellulose in wood remains unknown. Recently, oxalic acid (OA) has received considerable attention in cellulose breakdown by brown-rot fungi. The OA could serve as a proton donor for hydrolytic or an electron donor for oxidative (Fenton's reaction-H2O2/Fe2+) cleavages of cellulose. The acid may originate via oxaloacetase's action upon oxaloacetate. We report electron microscopic imaging (ESI) to localize Fe and HPLC/oxalic kit colorimetry to purify/quantify OA from hyphae upon agar, southern pine wood blocks (WBs) or in liquid culture. Comparative ESI at 25, 59, 110, 222, and 710 ev of hyphae grown upon agar or WBs demonstrated hyphal Fe (710 ev). Although Fe was not visualized in cell walls of uninoculated WBs, it was in certain wood cell walls of inoculated WBs. The Fe distribution differed from C and P. Oxaloacetase activity was not observed in either Amicon YM10 filter-retained intra-or extracellular fractions of liquid cultured hyphae or in homogenates from decayed WBs. In contrast, HPLC detected OA in both Postia placenta liquid cultures and decayed WBs. The less sensitive oxalic kit (mg vs. ug) did not detect OA in liquid cultures. These results constitute additional evidence for an OA Fe2+/H2O2-Fenton's mechanism for brown rot-induced cellulose degradation. However, OA's origin was not established.
C R Jordan, W V Dashek, T L Highley
Composting of waste building up in sawmill dipping basins
1990 - IRG/WP 3570
We have studied composting of waste building up in dipping basins at sawmills although this waste can also be disposed of by incineration. Controlled composting within the sawmill area seems to be a feasible method. Another possibility is to accomplish composting directly at the local dumping site. Waste containing antistain chemicals is generally classed as hazardous. It cannot therefore be placed as such at common dumps. However after successful composting the permission to do so can probably be obtained. The composted dipping basin waste might also be suitable as land filling or in some cases as soil improvement material - at least in parks and green belt areas.
I A Linderborg, U Ek
Early detection of brown-rot decay in southern yellow pine using immunodiagnostic procedures
1990 - IRG/WP 2356
Immunodiagnostic procedures have been used to detect incipient decay of southern yellow pine by six common brown-rot fungi. Rabbit polyclonal antibodies were raised to liquid culture fractions of the six fungi. The antibodies, after preadsorption to sawdust, were tested in particle agglutination assays, immuno-dot blot, and ELISA for their·ability to detect the decay organisms when they were grown in southern yellow pine. Results were correlated to wood block weight loss. Each method specifically detected five of the six test organisms at very low wood block weight loss. Agglutination assays were the least effective and lacked the sensitivity of the other assays, even though the latex particles were more sensitive and reproducible than charcoal particles. Cross-reactivity was only noted for one of the control organisms and only in the charcoal agglutination assay. Both dot blot and ELISA were sensitive test methods, but ELISA had the advantage of quantification. We feel that two of these assays, latex for presumptive results and ELISA for definitive results, could effectively detect incipient decay of common brown-rot fungi.
C A Clausen, F Green III, T L Highley
Comparing the resistance of a number of lesser known species of tropical hardwoods to the marine borer Limnoria using a short term laboratory assay
2003 - IRG/WP 03-10500
Naturally durable species of timber are used as an alternative to preservative treated timber for marine structures, but many species have not been evaluated for their potential for use in this environment. EN 275 specifies a 5-year test period - too long a period for screening tests to be economically viable. In this study, durability was assessed by measuring the production of faecal pellets by the crustacean Limnoria quadripunctata under forced feeding conditions over a number of days. Small sticks of a wide range of wood species, mainly of South American origin, were leached in seawater for one week then placed in a cell culture chamber with one animal and 4 ml of seawater. At intervals, the number of faecal pellets per chamber was counted, and the dimensions of the faecal pellets were measured. The number of pellets produced by animals feeding on Scots pine sapwood, which is non-durable, was used as a basis for comparison. Mortality rates were also compared. Lower pellet production rates and higher mortality rates were taken as measures of natural durability. Some lesser known species performed as well or better than species with a reputation for durability in the marine environment.
L M S Borges, S M Cragg, J R Williams
Qualifying ecotoxicity research on tropical hardwood leachates
1997 - IRG/WP 97-50096
Almost as a rule, quantification and identification of various types of environmental contamination is grounded on chemical evaluation principles. Yet for monitoring surface water pollution, aquatic bio-assays may provide a more direct way to assess the potential hazard of environmental samples. A battery of such tests is experienced onto leachates of tropical hardwoods used in ground and water contact. Four of seven wood species tested exhibited no acute toxic profile, whilst afzelia, afrormosia and mainly merbau revealed a considerable toxicity response for all organisms tested. These results, although at screening level, demonstrate the natural toxicity of particular tropical hardwood extractives towards the aquatic compartment. Hence, a welcome source of information is obtained, so as to weigh the ecotoxicity results previously gathered on preservative treated wood.
G M F Van Eetvelde, P Marchal, M Stevens
New approaches to practical evaluation method of bio-degradation of wooden construction - Non-destructive detection of defects using radar technique
2000 - IRG/WP 00-20214
There have been a number of researches and developments on the techniques and apparatus for the nondestructive evaluation of the biological deterioration in wood and wooden constructions, such as decay or insect attack in house, public buildings or in historically important architectures. As for the detection of the decay in wood, techniques using sound in audible or in ultrasonic frequency ranges, stress waves, heat wave and X- ray have been investigated, where the changes in the physical properties expressed in the wave form were related to decay. The change in the velocity, the attenuation or the frequency spectrum of these physical energy waves can be associated with the decrease of the specific gravity or the structural change due to decay. Some mechanical properties such as the boring resistance and the elastic properties of wood surface could be an indicator of decay. The dielectric property of wood and its relation to decay is also useful. Miller et al. (1989) applied a radar technique to diagnosing of standing trees. However the techniques previously developed are not always feasible. One of the possible reasons is that these physical or mechanical properties change not only on decay but also on other factors, such as the water content or the grain direction in wood. In addition, sometimes the techniques are less practical, strictly not non- destructive or too expensive. In practical maintenance operation of wooden constructions, visual inspection together with sampling method plays an important roll, however a specialized training is needed for the operator to get the skill of the diagnosing. In this study, to establish a practical evaluation method of bio- degradation in wooden construction, scanning using a newly developed portable radar apparatus was investigated. By comparing the results with other methods, a more practical method to evaluate the bio-degradation in wood was proposed.
Y Fujii, Y Komatsu, Y Yanase, S Okumura, Y Imamura, M Tarumi, H Takiuchi, A Inai
Fumigation of New Zealand grown western red cedar for export markets
2001 - IRG/WP 01-30262
The objective of this study was to demonstrate that methyl bromide fumigant penetrates into the centre of western red cedar (Thuja plicata L.) timber to meet the standard for export markets. Kiln dried western red cedar was used and a cavity (50x 30 x 13mm3) was prepared into the centre of each sample board (500 x 200 x 26 mm3 thick). An absorbent sachet used in industry for cross checking that the concentration of methyl bromide meets the standard during fumigation of export commodities was then inserted into the cavity. Two sample boards with individual sachets separated by aluminium foil and positioned at 13 mm below the wood surfaces, were then glued together. After curing of the glue, an aluminium tape was used to seal the four edges of the sample to prevent penetration of methyl bromide through the boards' edges. Fumigation was performed for 24 hours in the laboratory and also in a commercial environment using 80g of methyl bromide/m3 of wood prior to the cross checking of sachets. The results of this study demonstrated penetration of methyl bromide into the centre of kiln dried western red cedar (26 mm thick) in sufficient quantity to meet the specification for export to overseas markets.
B Kreber, G Durbin, D Wilson
Scandinavian experience – 25 years’ experience in transforming used creosoted wood into bio-fuel
2005 - IRG/WP 05-50224-18
Swedish experiences show that the best and most efficient way to handle the creosoted wood waste is through combustion. The preparation of creosoted waste wood to fuel chips at IQR AB’s plant in Trollhättan is done by splinting the wood according to a special method. Mainly railroad sleepers, but also other wooden commodities, from all over Europe are delivered to the plant. The wood material is crushed in a number of steps to achieve the appropriate size of the chips. The wooden chips are then delivered to combustion facilities in Sweden. The PAH emissions can be kept at a low level due to good mixing, high temperature and a high retention time in the furnace.
Preliminary evaluations of a small wafer assay for screening potential biological control agents
1989 - IRG/WP 2332
Screening potential biological agents for controlling wood decay fungi poses a dilemma. The ideal test would eliminate as many variables as possible. Most tests utilize pure cultures of the test organism on an artificial media which in no way resembles wood. The use of sawdust improves this approach, but the sawdust increases fungal access to the lignocellulose matrix, potentially inflating the importance of fungi which might not compete in the normal wood system. This report describes a simple wafer sandwich assay in which small test wafers colonized by the potential biocontrol agent and a Basidiomycete are placed above and below a sterile test wafer on moist soil in a glass petri dish. Weight loss of the middle wafer is used as a measure of biocontrol potential. Preliminary trials indicate that several previously identified biocontrol agents performed well in this test, inhibiting wood weight losses by both white and brown rot fungi. Because the wood structure is not disturbed, this method could also be used to screen wood treatments which might enhance colonization by the biological control agent.
C M Freitag, J J Morrell
Improved preservative penetration of spruce after pre-treatment with selected fungi. I. Fungal pre-treatment of pole sections
1998 - IRG/WP 98-40117
European spruce logs were pre-treated with either Phanaerochete chrysosporium, Dichomitus squalens, Trichoderma viride and Trichoderma aureoviride for incubation periods of between 1-4 weeks prior to pressure treatment with creosote in a commercial treatment plant and analysed for strength and creosote uptake (see part II Tucker et al.). A method to pre-treat logs was optimised. The pole sections were surface sterilised, inoculated with a spore suspension or blended fungal mycelium and supplemented with a nutrient solution. The colonisation of the logs was investigated by light microscopy, SEM and by an ergosterol method, quantifying the fungal biomass in the wood. The assays indicated a rapid and even colonisation of the wood down to the heartwood within a period of approximately 1 week. Dichomilus squalens was also seen to colonise the heartwood. The microscopic and quantitative assays correlated well and reflected the depth of penetration of creosote on subsequent treatment. SEM observations showed that the increased permeability is due to an enzymatic opening of the pit membranes rather than physical penetration of the pits by fungal hyphae.
B Rosner, K Messner, E J B Tucker, A Bruce
Comparison of two laboratory methods for screening potential anti-sapstain chemicals
1993 - IRG/WP 93-10036
Two methods were used to screen a number of potential anti-sapstain chemicals in the laboratory. In one method miniature boards of freshly felled Scots pine sapwood were dip treated with the candidate chemical, sprayed with a suspension of stainers or moulds and incubated for five weeks. In the other method antibiotic assay discs were treated with precise quantities of chemical, plated out on malt extract agar, inoculated with a spore suspension of one of four stainers and moulds and incubated for a few days. This was repeated for each of the four fungi. The results obtained from the two methods provided information on different aspects of the chemicals but the overall conclusions on efficacy were the same.
S M Gray, D J Dickinson
The potential application of rapid gas-chromatographic assay of microbial respiration to the monitoring of wood decay in field trial situations
1983 - IRG/WP 2196
Gas chromatographic detection of microbial activity (C02 production) within stakes in a field trial situation would appear to provide a sensitive, non-destructive and relatively rapid method for the quantitative assessment of preservative treatments. Most consistent results were obtained when stakes were removed from the soil, washed, saturated with water and incubated in sealed PVC tubes at 25°C for 24 h prior to assay of gas samples from the tubes. Each assay took 1.6 min to perform and stakes were returned to the field within 48 h. Microbial activity was readily detected in untreated Eucalyptus regnans stakes after 18 days field exposure. Stakes pressure impregnated with CCA, busan-30 or creosote displayed consistently low levels of activity to the present time (3 months after insertion).
M A Line
Degradation of polycyclic aromatic hydrocarbons by laccase
1998 - IRG/WP 98-10267
The degradation of polycyclic aromatic hydrocarbons (PAH) by laccase was investigated. Laccase catalyzed oxidation of phenanthrene, solubilized in the surfactant Tween 20, exhibited an absolute requirement for the mediator compound 1-hydroxybenzotriazole. When Tween 80 was used as the solubilizing agent, the oxidation rates were more than six times higher as compared to Tween 20. Using the thiobarbituric acid (TBA) assay, it was shown that the laccase-HBT couple peroxidized linoleic acid. The results suggest that unsaturated fatty acids present in Tween 80 are responsible for the enhanced degradation of phenanthrene by laccase-HBT. The system comprising laccase, HBT, and Tween 80 was applied to the sixteen EPA priority PAH with the result that all of the PAH were extensively degraded.
S Böhmer, E Srebotnik, K Messner
Performance of Copper-Chrome-Arsenic (CCA) and Copper-Chrome-Boric (CCB) treated panels of Bombax ceiba and Paraserianthus falcataria against bio-deterioration at Krishnapatnam harbour, east coast of India
2003 - IRG/WP 03-30310
Results of investigations on the durability of light weight timber species (Specific gravity below 0.4) i.e., Bombax ceiba and Paraserianthus falcataria in treated and untreated condition conducted at Krishnapatnam harbour (Lat 13o28’ to 13o59’ N; Long: 80o10’ to 80o16’E) along the east coast of India are reported in the paper. Exposure trails were conducted with panels (Size: 30 x 3.8 x 3.8 cm.) treated with CCA (Copper–Chrome–Arsenic) and CCB (Copper-Chrome-Borate) at four retention levels (8, 16, 24, and 32 kg/m3), for a period 3 years from August, 1997 to July, 2000. Control panels of both the species were heavily attacked by shipworms and pholads and rejected in a period of 3 months. On these, panels, shipworms attained maximum growth of 2.3 cm. and pholads 1.4 cm. On these panels. borer species identified were: Martesia striata, M. nairi, Teredo furcifera, T. fulleri, Lyrodus pedicellatus, and Bankia campanellata. Timber panels treated with CCA at lower loadings (8 and 16 kg/3) had greater number of shipworms (>200) than pholads. Shipworms and Pholads attained maximum growth of 2.6 and 1.8 cm respectively. Panels treated with higher loadings (24 and 32 Kg/m3) had more pholads (>150) than shipworms. Pholads and shipworms attained maximum growth of 3.1 and 6.8 cm respectively on these panels. The CCB treated panels of lower loadings also had heavier shipworms (>300) that attained maximum growth of 16 cm, whereas, pholads attained a maximum of 2.2 cm. On higher loadings of CCB treated panels, pholads intensity was observed to be greater and attained a growth of 3.4 cm while shipworm attained 1.9 cm. Overall, shipworm intensity was found to be greater on CCA and CCB panels with lower retentions (8 and 16 Kg/m3), whereas penetration was not deep on higher loadings (24 and 32 Kg/m3). CCA treated panels with lower loadings (8 and 16 Kg/m3) were found to be better than those of lower loadings of CCB. However, at higher loadings (24 and 32 Kg/m3) variations were not significant.
B Tarakanadha, N R Raveendra Prasad, K S Rao