Abstract
The conventional stake test is widely used to evaluate wood durability. The test monitors the deterioration level observed on stakes partially inserted into the ground. The test results are conventionally expressed as the relationship between the mean deterioration level and exposure periods. Durability is compared between the stake groups based on the test results; however, there is no scientific basis for the comparison. To include a scientific basis to the conventional stake test, we applied survival analysis to it. Four stake groups were subjected to deterioration at three sites for 7 years. The deterioration levels were monitored according to the conventional procedure, and survival analysis was applied to the monitored data. The Kaplan–Meier curves plotting the survival probabilities against the exposure periods indicated that the durability of the test stakes of Japanese cedar heartwood is higher than those of Japanese cedar sapwood. However, it was also demonstrated that the durability ratio between Japanese cedar heartwood and sapwood was strongly dependent on the test sites. It was also revealed that the durability of the heartwood portion did not differ significantly among Japanese cedar, Japanese cypress, and Japanese larch. These results were verified using the modified Gehan–Wilcoxon test.
Highlights
Wood is a material that mitigates global warming via the carbon stock, material substitution, and energy substitution effects [1,2,3]
Close and open circles indicate the mean deterioration levels of Japanese cedar sapwood (Ced-S) and Japanese cedar heartwood (Ced-H) observed during each exposure period
As shown in the figure, the mean deterioration levels of Ced-S and Ced-H increased with an increase in the exposure period and reached 2.5 in approximately 2.0 and 2.7 years, respectively
Summary
Wood is a material that mitigates global warming via the carbon stock, material substitution, and energy substitution effects [1,2,3]. The replacement of concrete/steel materials by wooden ones has led to reduced carbon dioxide emissions [4,5,6]. In addition to increasing the volume of the carbon stock effect, trials have been conducted to prolong its lifespan by increasing the shelf life of wooden materials to reduce global warming. The observed stake deterioration levels are evaluated according to the criteria for each standard. Japanese Industrial Standard (JIS) K 1571 [17] defines the sound stake and broken stake deterioration levels as 0 and 5, respectively. The durability of each treatment group is Momohara et al J Wood Sci (2021) 67:44 compared based on the year when the mean deterioration level reaches 2.5
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