Experimental Study on Resistance of Calcium Leaching and Crystallization of Tunnel Shotcrete Admixtures

In order to alleviate the crystallization blockage of drainage system caused by calcium leaching of tunnel shotcrete, based on the investigation of a variety of concrete admixtures, anti-alkali agent and nano-SiO₂, fly ash and nano-CaCO₃ were selected from two aspects of consuming free Ca(OH)₂ and filling concrete pores, for indoor single-mixing test. From four aspects of the crystallization of the drainage pipe, the concentration of calcium ion in the leaching solution, the change of the flow rate of the leaching solution and the total amount of calcium leaching calculated, the admixture with better effect of reducing calcium leaching and crystallization and its optimal dosage were selected through the intra-group comparison between different admixtures and the comparison under different dosages of the same admixture in the test. The results show that: anti-alkali agent with 9% dosage has the best effect of the resistance of calcium leaching and crystallization in the aspect of consuming free Ca(OH)₂; nano-CaCO₃ with 6% dosage has the best effect of the resistance of calcium leaching and crystallization in the aspect of filling concrete pores. The results of the study can provide some reference for the prevention of the disease of crystallization blockage in tunnel drainage system.