Study on the Durability Performance of Shotcrete Lining Under Coupling Effect of Nitric Acid Attack and Freeze-thaw Cycles (Part I):Deterioration Law of Performance and Air-void Structure
WANG Jiabin1, NIU Ditao2,3
1 School of Civil & Architecture Engineering, Xi'an Technological University, Xi'an 710021 2 College of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an 710055 3 National Key Laboratory of Green Building in West China, Xi'an University of Architecture and Technology, Xi'an 710055
Abstract: As the engineering background of long tunnel with shotcrete single-layer lining in the cold area, freezing and thawing test of shotcrete was carried out using rapid freeze-thaw mothed and nitric acid solution which formed by nitrogen oxide in automobile exhaust and vapor. The performance deterioration of dynamic elastic modulus, mass and compressive strength was investigated. Afterwards, a high-resolution image analyzer capturing elaborate graphical layouts of air-void structure using the linear transverse method was employed to study the damaged process of shotcrete under coupling effects. The results show that hydrogen ion of nitric acid solution produces chemical reaction with hydration products of shotcrete, and the salt frost phenomenon is appeared in freezing and thawing by effect of nitrate ion. Therefore, nitric acid accelerates shotcrete frost damage speed. Frost resistance of shotcrete with coupling action depends to mix proportion in term of water-binder ratio, dosage of fly ash and steel fiber content. With water-binder ratio increased, shotcrete frost resistance decreased. While the performance increased at first and then decreased with fly ash replacement increased. With steel fiber content increased, the loss ratio of dynamic elastic modulus and mass increased firstly and then decreased, while compressive strength increased. About air-void structure, with increasing of freeze-thaw cycles, air-void structure deteriorates and number of harmful voids and microcracks increases, what causes nitric acid diffusing in shotcrete and leads to the frost resistance of shotcrete decreasing rapidly.
王家滨, 牛荻涛. 硝酸侵蚀/冻融循环共同作用喷射混凝土耐久性能(I):物理力学性能及孔结构变化[J]. 材料导报, 2019, 33(8): 1340-1347.
WANG Jiabin, NIU Ditao. Study on the Durability Performance of Shotcrete Lining Under Coupling Effect of Nitric Acid Attack and Freeze-thaw Cycles (Part I):Deterioration Law of Performance and Air-void Structure. Materials Reports, 2019, 33(8): 1340-1347.
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