西北复合盐侵蚀环境衬砌喷射混凝土离子扩散研究

中国西北地区盐渍土广泛分布，侵蚀性离子与喷射混凝土衬砌接触并向其内部扩散，经过一系列物理化学作用，形成高溶解性、膨胀性及无胶凝性侵蚀产物，破坏喷射混凝土微观结构，造成衬砌结构耐久性退化。采用干湿交替制度，模拟西北地区自然环境；以5%Na2SO4+5%MgSO4+3.5%NaCl(质量百分比)混合溶液为侵蚀介质，模拟盐渍土及其地下水中的离子组成及含量，开展复合盐侵蚀喷射混凝土耐久性试验，测试混凝土pH值，水溶性Cl-、SO2-4、Ca2+含量及酸溶性SO2-4含量。结果表明：干湿交替次数增大，混凝土pH值，水溶性Ca2+含量降低，水溶性Cl-、SO2-4及酸溶性SO2-4离子含量增大。Mg2+扩散导致混凝土侵蚀区pH值明显降低。但随着深度增大，混凝土pH值快速增大继而稳定。Cl-扩散降低酸溶性SO2-4含量，而SO2-4的扩散加速混凝土pH值及Ca2+含量降低，并在一定程度上促使Cl-含量提升。喷射混凝土的水胶比、粉煤灰取代率及钢纤维掺量对离子扩散具有显著的影响。喷射混凝土中水溶性Cl-及SO2-4扩散符合Fick第二定律，并建立了考虑喷射混凝土配合比参数的离子扩散模型。

Ion diffusion in shotcrete lining under compound salt corrosion #br# environment saline soil in Northwest China

Saline soil widely distributes in Northwest China. Aggressive ions can diffuse into shotcrete lining, and after a sequence of physical and chemical reactions, corrosion products with the characteristics of high solubility, expansion and non-gelling are produced, which destroys the microstructure of shotcrete and leads to the degeneration of the durability of lining structure. The durability of shotcrete exposed to compound salt was tested under drying-wetting cycles to simulate the environment of Northwest China. Furthermore, the corrosive medium of 5%Na₂SO₄+5%MgSO₄+3.5%NaCl (mass ratio) solution was used to simulate the composition and content of aggressive ions in saline soil and the underground water, and the experiments on the durability of compound salt corroded shotcrete were carried out for measuring the pH value, the contents of water-soluble Cl^-, SO ^2-₄ and Ca2+ and the content of acid-soluble SO ^2-₄. The results show that with the increase of drying-wetting cycles, the pH value and the content of water-soluble Ca ²⁺ of shotcrete decrease, while the contents of water-soluble Cl^- and SO ^2-₄ and the content of acid-solubleSO ^2-₄ increase. The diffusion of Mg²⁺ into shotcrete may result in the evident decrease of the pH value of corrosion zone. However, the pH value quickly increases and then remains stably with the depth. The diffusion of Cl- decreases the content of acid-soluble SO ^2-₄, while the diffusion of SO ^2-₄ accelerates the decrease of the pH value and the content of Ca²⁺, and to some degree promotes the increase of Cl- content. Meanwhile, the water-binder ratio, fly ash replacement ratio and steel fiber content may significantly affect the diffusion of ions. The diffusions of water-soluble Cl^- and acid-soluble SO ^2-₄ into shotcrete conform to the Fick's second law, and the diffusion model of ions considering the mix-proportion parameter of shotcrete was established.