尿素包装厂房结构混凝土损伤调查与损伤机理分析

Analysis of damage mechanism of structural concrete of urea packing plant buildings

安庆石化尿素包装厂房混凝土结构出现较大面积的破坏现象,为评定其结构使用状况,对其混凝土结构进行现场调查和试验室测试。现场检查发现该厂房混凝土已发生严重的腐蚀,这些损伤大多伴随着尿素结晶存在。用体视显微镜和X射线衍射以及红外光谱分析等方法对现场钻取的芯样进行研究,结果表明:从混凝土表面逐步向内约40mm范围内混凝土基本上被尿素腐蚀,并有进一步扩展的趋势。分析混凝土损伤的主要原因既有物理作用,也有化学作用。物理作用是尿素在混凝土中的结晶导致混凝土膨胀开裂;化学作用则主要是尿素与混凝土中的碱作用加速了混凝土碳化。尿素分解的氨与混凝土中的碱作用也加剧混凝土的碳化,并且产生的水分引起进一步的腐蚀,特别是加剧钢筋腐蚀。物理作用和化学作用共同作用下导致混凝土损伤腐蚀;环境湿度对腐蚀起到重要的作用。

Extensive deterioration of the concrete structure of the Anqin urea packing plant has been observed. To assess the structural durability and status of the building, extend of the concrete damage is investigated, and the damage mechanism studied. The investigation includes visual inspection of the exteriors, stereomicroscope sample study, diffracted X-ray and infrared imagery. The concrete is found to be in a state of severe erosion. Study of core samples from typical areas indicates that urea has gradually corroded about 40 mm into the surface of the concrete, and this trend will probably continue. It is concluded that the main causes of the damage are of two-fold： physical action and chemical reaction. Physical action is due to the crystallization of urea inside the concrete causing it to expand first and then crack. Chemical reaction between urea and alkali in the concrete accelerates the carbonization. The excessive ammonia produced in the production process and the decomposition of urea further speeds up the concrete carbonization, and the additional water thus produced causes further corrosion, especially to the reinforcement steel bars. The combination of physical action and chemical reaction causes corrosion damage to concrete, and environment humidity also plays an important role in the corrosion.