Comparison of durability of treated wood using stake tests and survival analysis

Ikuo Momohara,Yuji Kubo,Haruko Sakai

doi:10.1186/s10086-021-01996-2

Ikuo Momohara, Yuji Kubo + Show 1 more

Open Access

https://doi.org/10.1186/s10086-021-01996-2

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Abstract

The stake test is widely used to evaluate the efficacy of wood preservatives. This test monitors the deterioration level observed in treated stakes partially inserted into the ground. The results are conventionally expressed as the relationship between deterioration levels and exposure periods. The preservative efficacy is compared among the stake groups treated with different retention levels based on the test results; however, there is no scientific basis for the comparison. We applied survival analysis to the conventional stake test to include a scientific basis to the test. Stakes impregnated with different types and retention levels of preservatives were subjected to deterioration at two test sites for approximately 30 years. The deterioration levels were monitored according to the conventional procedure and survival analysis was applied to the monitored data. Kaplan–Meier plots of the survival probabilities against the exposure periods indicated that there is a significant difference between the durability of the stakes treated with alkylammonium chloride (AAC-1) at K2 and K3 retention levels, whereas no significant difference was observed between those at K3 and K4 retention levels. Contrastingly, emulsified copper naphthenate (NCU-E) was found to be a reliable preservative, and the stakes impregnated with NCU-E showed a significant increase in durability in accordance with preservative retention. Alkaline copper quaternary (ACQ-1) also appeared to be a reliable preservative; however, the increase in stake durability after ACQ-1 treatment differed between the test sites. These results were verified using the modified Gehan–Breslow–Wilcoxon test with Holm’s p adjusting method.

Highlights

Wood is a material that mitigates climate change [1–3]; many trials have been conducted to prolong its durability by increasing the service life of wooden materials
We developed a conventional stake test method with the addition of survival analysis and demonstrated that the novel method is useful for comparing durability among groups of untreated stakes [13]
1) We applied a survival analysis to the conventional stake test to compare the efficacy of preservatives

Summary

Introduction

Wood is a material that mitigates climate change [1–3]; many trials have been conducted to prolong its durability by increasing the service life of wooden materials. Chemical or thermal modification processes have been recently adopted [4, 5], preservative impregnation by a vacuum-pressure process has been the most common method for increasing the durability of wooden materials [6–9]. Preservatives used for this process have been developed over several decades. 30 years ago, chromated copper arsenate (CCA) was widely used for sill members in Japanese houses. We present the application of survival analysis to the stake test data and discuss the effect of preservative retention on the durability of treated stakes

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Conclusion