Study on the durability performance of shotcrete under coupling effect of nitric acid attack and freeze-thaw cycles — Part II: pH value and NO -3diffusion
Wang Jiabin1,2 Niu Ditao2,3 He Hui1 Wang Bin1 Song Zhanping3
1. Xi’an Technological University, Xi’an 710021, China;
2. National Key Laboratory of Green Building in West China, Xi’an University of Architecture and Technology, Xi’an 710055, China;
3. College of Civil Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China
Abstract：In order to further study the durability degradation mechanism of shotcrete under coupling effect of nitric acid attack and freeze-thaw cycles, by using solid liquid extraction method and electrochemical method, pH value and nitrate ion content testing are carried out considering the influence of frost damage and shotcrete mix proportions. The results show that micropores in shotcrete under coupling effect continue to be formed and transformed into macropores which interconnect into cracks. With the increase of freeze-thaw cycles, pH value of shotcrete gradually decreases and nitrate ion content increases. For shotcrete with high water-binder ratio and/or high content of fly ash, pH value is low and nitrate ion content is high. Compared with shotcrete without steel fiber, the variation range of ions content of steel fiber reinforced shotcrete is relatively small. Therefore, the frost resistance of steel fiber reinforced shotcrete is high. Coupling effects make shotcrete suffer from hydrogen ion, nitrate ion and freeze-thaw cycle. Under the chemical attack of nitric acid, pH value of concrete quickly decreases and nitrate ion content increases, hydration products are eroded and/or decomposed which leads to the hange of mineral composition. Meanwhile, under the influence of salt frost damage produced by nitrate ion and freeze-thaw cycles, mortar and aggregate on the shotcrete surface peel off, leading to loose and air-void structure as well as deterioration of the physical and mechanical properties.
王家滨 牛荻涛 何 晖 王 斌 宋占平. 硝酸侵蚀/冻融循环共同作用下喷射混凝土耐久性能(II)——pH值及NO -3扩散#br#[J]. 土木工程学报, 2019, 52(7): 1-12.
Wang Jiabin Niu Ditao He Hui Wang Bin Song Zhanping. Study on the durability performance of shotcrete under coupling effect of nitric acid attack and freeze-thaw cycles — Part II: pH value and NO -3diffusion. 土木工程学报, 2019, 52(7): 1-12.
