山西白台寺古榆木檐柱的劣化机制

Deterioration of the Ancient Ulmus Wood Served as Eaves Column Replaced from Baitai Temple in Shanxi Province

使用现代分析手段对山西省唐代建造的白台寺替换的距今(970±28)a的古榆木(Ulmus sp.)檐柱的宏观和微观特征、密度、尺寸干缩率、化学组分和纤维素结晶度等进行了分析,系统评价了该古榆木檐柱的腐朽机制、虫害类型、物理性质和化学组分的变化。结果表明:该檐柱的劣化与其所处建筑部位紧密相关。显微镜分析显示埋藏于土墙中的檐柱部分受到了窃蠹甲虫成虫和幼虫的严重啃食,是导致檐柱破坏的最重要因素。甲虫幼虫主要在木材内部破坏造成了檐柱部分空心,而成虫则主要破坏与墙体直接接触部分的木材。未与墙体接触且曝露室外的檐柱部分基本没有受到窃蠹甲虫的侵害,其降解类型主要是软腐,且腐朽处于初期阶段,对木材的密度、最大吸水率和尺寸干缩率均未造成明显影响。红外光谱和组分分析显示,整个檐柱各部分的木质素均未出现实质性降解,但X射线衍射仪表明,墙体外檐柱外层的半纤维素和结晶度含量要比内部低。综上所述,檐柱的劣化主要是由土墙内的窃蠹甲虫侵害和软腐菌生长造成,在白台寺的后期修复与保护中应当及时更换或加固泥墙中的承载梁柱并进行防窃蠹甲虫处理,对泥墙外的木结构则需要进行防软腐处理,阻止软腐的进一步加剧。

An ancient ulmus(Ulmus sp.)wood eaves column that date from 970±28 a ago was replaced from the historical Baitai Temple constructed in Tang Dynasty in Shanxi Province,P.R.China,and its macro-and micro-structure,density,dimensional shrinkage,chemical compositions,and crystallinity were analyzed.The deterioration status of the ulmus column after standing for approximately 970 a was systematically evaluated resulting from fungal decay,insect damage,and changes in physical properties and chemical compositions.The results showed that the deterioration of the ulmus column was closely dependent on the position in the construction.The microscopic analysis indicated that damage by larcenous beetle damage was the main deterioration mode for column buried in the mud wall;the larvae encroached on the column interior and the imagoes damaged the outer part contacting with mud wall.The wood column out of mud wall was almost free of beetle damage,but was subjected to soft rot.The soft rot was still in the initial stage and had little effect on the wood’s density,maximum water uptake,and dimensional shrinkage.The FT-IR and cell-wall composition analysis revealed that lignin content in the whole column was comparable and XRD indicated that the crystallinity of the outer part of the unburied column was lower than that of the column interior.The results confirm that the beetle and soft rot are the main deterioration modes of the ulmus wood column.The wooden structures in Baitai Temple require to be restored and protected to prevent wood from further deteriorating.Part of load-bearing columns and beams shall be strengthened or replaced.