Accelerated testing for out of ground contact using natural biological preconditioning: Part 2

IRG/WP 97-20108

S Molnar, D J Dickinson, R J Murphy

Small blocks of scots pine sapwood were treated, buried in vermiculite and exposed to natural microbial colonisation during outdoor exposure prior to laboratory decay testing. An EN 84-type leach trial was carried out on unexposed samples. Periodic microbial isolations, moisture content, permeability and weight loss tests were also conducted. The experiment ran for 12 months. The colonisation of the miniblocks by micro-organisms was rapid and different patterns of colonisation were observed for differently treated miniblocks. The dominant organisms throughout were Alternaria sp., Fusarium sp., Curvularia sp., Aureobasidium pullulans, Phialophora sp. and bacteria. Weight losses of 10% occurred in the field by 12 months with untreated samples. DDAC- and TnBTO-treated miniblocks (at the recommended commercial retention) had weight losses of 7% and 8% respectively. ACQ treated samples at this retention had the lowest weight losses at only 1.5%. Of the treated samples, TnBTO-treated blocks had the most rapid rate of weight loss and also the fastest increase in permeability. TnBTO-and DDAC- treated samples had equivalent final permeabilities, at double the value of the ACQ-treated blocks. The decay trial indicated that this natural pre-exposure method was very severe with reduced performance of all treatments in the monoculture Basidiomycete tests after 12 months of pre-exposure. The comparative leaching trial showed that the failure of the preservatives was not due only to severe leaching in the test system. The white rot decay test indicated that at all retentions TnBTO- and DDAC-treated miniblocks had reached over 3% weight loss by 3 months pre-exposure but for ACQ this weight loss was not reached until 12 months. In the brown rot test at all retentions of TnBTO and ACQ weight losses of over 3% were reached by 3 months and for DDAC by 6 months.


Keywords: NATURAL EXPOSURE PRECONDITIONING; TnBTO; DDAC; ACQ; MINI-BLOCKS; AGAR-BLOCK TRIALS

Conference: 97-05-25/30 Whistler, British Columbia, Canada


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