Deterioration rates of pressurizing-compression-treated wood used in erosion
and flood control wooden structures and effects of freezing and thawing

Tsukasa YOSHIDA, Yoshiharu ISHIKAWA, Yoshihiro TSUJIMOTO and Yoshihisa TAJI

We used a resistograph to measure the deterioration rate of processed wood used in Azekura wooden structures at 15locations built 5]15years before the survey. The wood had been subjected to compression treatment and pressure]injected with preservatives (this wood will be referred to hereinafter as “pressurizing]compression]treated wood"). We conducted the same measurement at two locations on non]processed wood that had not been subjected to such treatment. The results revealed that the pressurizing]compression]treated wood had a markedly lower deterioration rate than non]processed wood. A major difference in deterioration rates of the main body and wing of the consolidation dams depending on whether the dam is always wet with water (wetness or dryness) has been reported in previous research, but no such difference was observed in the pressurizing]compression]treated wood. Based on these findings, we may conclude that while most of the deterioration in non]processed wood results from rot, in pressurizing]compression]treated wood, which resists rot, the difference in deterioration rate depended on the wetness or dryness of the bodies and wings of the consolidation works will largely disappear. An analysis of the relationship between environmental factors and deterioration revealed that the deterioration rate of pressurizing]compression]treated wood was negatively correlated with annual mean temperature and annual precipitation. We also conducted a freeze]thaw test on the wood, which revealed that increasing the freeze]thaw cycle significantly increases the thickness of the deteriorated part. Based on these results, we can conclude that, as reported in existing literature, deterioration rate is positively correlated with annual mean temperature and annual precipitation in the case of non]processed wood because it is strongly affected by rot and other forms of biodeterioration. However, in pressurizing]compression]treated wood, because wood preservatives minimize the deterioration rate, physical deterioration (by freezing and thawing) has a relatively large impact, and the deterioration rate is negatively correlated with annual mean temperature and annual precipitation.