Study on Curing Mechanism of Nitrite Type Cl- Curing Agent in Sea Sand Concrete
MING Yang1,2,3,4, XIAO Dengkai1,2,4, LI Ling1,2,3,4,*, LI Xinheng1,2,4, ZHU Qiyang1,2,4, HUANG Dengke1,2,4, REN Hao1,2,4
1 College of Civil Engineering, Guilin University of Technology, Guilin 541004, Guangxi, China 2 Guangxi Key Laboratory of Green Building Materials and Construction Industrialization, Guilin 541004, Guangxi, China 3 Collaborative Innovation Center for Exploration of Nonferrous Metal Deposits and Efficient Utilization of Resources, Guilin University of Technology, Guilin 541004, Guangxi, China 4 Guangxi Engineering and Technology Center for Utilization of Industrial Waste Residue in Building Materials, Guilin 541004, Guangxi, China
Abstract: The large amount of chloride ions contained in sea sand is the main bottleneck hindering its application in cement-based materials. In this work, three materials, NaAlO2, Ca(OH)2, and Ca(NO2)2, were used to prepare a new nitrite-type chloride ion curing agent (NO2-ClCA) by hydrothermal method. Through adding this agent in the cement-based materials, it showed a good chloride ion curing ability. Finally, the mechanism of NO2-ClCA was analyzed using XRD, SEM and other methods. The results showed that the optimal method to get NO2-ClCA is with the mass fraction of NaAlO2 and Ca(NO2)2 of 15% and 6%, respectively, the stirring rate of 30 r/s, and the reaction temperature of 60 ℃. By adding NO2-ClCA to cement-based materials, chloride ion curing of 1.33 mg/g can be achieved. The main components of NO2-ClCA are NO2--AFm and C3AH6. The curing effect of NO2-ClCA on chloride ions is mainly chemical curing. Specifically, NO2--AFm reacts with free Cl- in the pore solution to form Friedel's salt, which improves the chemical binding capacity of the system. C3AH6 participates in the anion replacement reaction and supplements the calcium and aluminum phases in the system, which can promote the conversion of C-S-H gel to C-(A)-S-H gel to improve the physical adsorption capacity of the system.
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