盐湖卤水侵蚀喷射混凝土衬砌损伤演化

Damage Evolution of Shotcrete Lining Under Salt-lake-brine Attack

我国西部地区盐湖分布广泛,土壤及地下水中含有高浓度硫酸盐、镁盐及氯盐,其会与衬砌喷射混凝土发生一系列物理化学反应,导致混凝土表面损伤并不断演化,继而造成衬砌结构可靠度下降。为系统研究盐湖卤水侵蚀喷射混凝土损伤形成及演化规律,以5%Na 2SO 4+5%MgSO 4+3.5%NaCl复合盐溶液为侵蚀介质,采用干湿交替法,分别模拟盐湖卤水及衬砌结构侵蚀方式,开展喷射混凝土损伤演化试验。通过对喷射混凝土侵蚀产物的组成及含量、微观形貌和离子含量进行综合分析,系统研究了卤水侵蚀混凝土的损伤演化机理。结果表明:喷射混凝土中的SO42-含量随侵蚀时间的延长而快速增大,Cl-和Na^+含量缓慢增大,而Ca^2+含量和混凝土pH值降低。喷射混凝土卤水侵蚀过程包含水镁石、石膏及钙矾石层形成阶段,C-S-H分解及碳硫硅钙石形成阶段以及水化硅酸镁凝胶形成等三个阶段。期间,结晶盐在毛细孔及微裂缝中不断累积,加速了混凝土的损伤演化。最终,在碳硫硅钙石、水镁石、石膏、钙矾石以及结晶盐所形成的膨胀应力和结晶压力共同作用下,喷射混凝土内部及表面形成网状裂纹,骨料剥落,损伤厚度快速增大。

Salt lake is widely distributed in Western China.The high concentrations of chlorine salt,sulfate,and magnesium salt in the soil and underground water are the major reasons leading to the damage evolution of lining shotcrete and reliability of lining structure decreased.In order to research the damage appearing and evolution laws of shotcrete lining in brine corrosion environment,by using dry-wet cycle(D&W)method for simulating the corrosion mode of tunnel lining,the shotcrete durability experiment was carried out in 5%Na 2SO 4+5%MgSO4+3.5%NaCl solution.Mineral composition and microscope of corrosion products,and ions content were tested by using XRD,TG-DSC,SEM&EDX and electrochemical method,respectively.Acid-soluble sulfate content obviously increased with the increase of D&W cycle,and water-soluble chloride and sodium content slowly increased.However,calcium content and concrete pH value decreased.The corrosion process of brine-exposed shotcrete includes three stages of brucite,gypsum and ettringite formation,C-S-H decomposition and thaumasite formation,and M-S-H formation.During the three stages,crystal salts accumulated in micropores and microcracks which accelerated the deterioration speed.Finally,as combined action of expansion stress and crystallization pressure which come from thaumasite,brucite,gypsum,ettringite and crystallized salt,web cracks are formed in shotcrete and surface,which caused damage evolution quickly of shotcrete lining.