Scientists at Stellenbosch University have completed long-awaited research into the adequacy of the standard for CCA retention in eucalyptus poles.
The study results show that CCA retentions in vineyard poles should increase for adequate durability. The South African Wood Preservers Association (SAWPA) will send the results to the industry soon for discussion and a technical recommendation.
After that, the South African National Standards stand to be amended in line with the study’s findings.
The research was a collaborative effort between the timber treatment industry and the university to determine the adequacy of the CCA retention levels for eucalyptus poles outlined in the SANS, explained SAWPA Executive Director Bruce Breedt.
It followed concerns about whether vineyard poles were adequately treated to avoid fungal decay, and soft rot in particular, for the moist conditions in which they were planted.
“Meanwhile, information gathered from international sources had indicated that CCA retentions in the treatable sapwood parts of the timber should be increased when the poles are used in high-risk areas.”
The study was launched eight years ago. “Unfortunately, when the initial results and data were reviewed, certain shortcomings in the data and methodology became apparent,” said Bruce. “These had to be reviewed – and the study had to be repeated. Then the Covid-19 pandemic struck, which delayed the process further.”
Meanwhile, information gathered from international sources had indicated that CCA retentions in the treatable sapwood parts of the timber should be increased when the poles are used in high-risk areas.
As an interim measure, until the ideal retentions were established, the SANS were amended to increase the chemical retention in poles to H5 level, while retaining the minimum H4 penetration.
For the study, a representative sample of the poles in question was gathered from eucalyptus plantations across South Africa. These poles have a relatively small diameter of between 50 and 150mm, and a large sapwood area.
“The study was separated into three different phases: firstly, determining the typical sapwood ratios of small-diameter poles; then determining the density of these poles, and thirdly, what the optimum or acceptable sapwood retention needs to be to ensure an acceptable service life,” explained Bruce.
The retention was determined by an accelerated laboratory fungal soil bed test, as an in-field study would take decades.
SAWPA was fortunate to have the hands-on involvement of Emeritus Professor Tim Rypstra in the repeat of the study, “which only recently came to a close, its results showing what retention levels need to be to give an acceptable service life for CCA-treated eucalyptus poles and possibly those used in other high-risk agricultural applications.”
The adoption of the changes into the SANS can be a long process, as the recommendations must go to the SANS committee before being adopted.
“But the good thing is that the research part of the process is finished,” said Bertus.
The study findings regarding retentions are similar to retention levels implemented in other countries and regarded as international best practice, he pointed out.
“We look forward to working with the industry to reach a decision, as a part of our commitment to make sure that our products meet service-life expectations,” said Bertus.
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