Metakaolin (MK) is a widely used admixture in chloride immobilization which is conducive to the durability of reinforced concrete. In this study, triisopropanolamine (TIPA) was added into cement-MK system to improve the chloride immobilization by expediting the pozzolanic reaction of MK. The effect of TIPA on hydration of binder composed of 90% Portland cement and 10% MK was investigated, and the hydration behavior was characterized by thermogravimetric analysis , X-ray diffraction, nuclear magnetic resonance spectroscopy , and mercury intrusion porosimetry , based on the evaluation of pozzolanic reaction of MK by ion dissolution. Results indicated that TIPA promoted the hydration of both MK and cement, and chloride immobilization was also improved. The mechanism for the improvement was involved in three aspects: a) TIPA facilitated the dissolution of aluminum from MK to obtain more chloroaluminate salts, strengthening chemical binding; b) TIPA accelerated hydration of cement and MK for more C-S-H gel, conducive to the physical adsorption; c) TIPA increased the amount of hydrates to refine the pore structure , hindering the migration of chloride ion. This investigation provided one new method for improving the pozzolanic reaction of MK to enhance chloride immobilization of cement-MK system.
Dongping Song,Tao Huang,Kai Chen,Jialin Cui,Qingyang Xu,Chengyu Yan,Chengzhe Yang,Shaohang Wan,Minfeng Tao
In this study, the magnesium phosphate cement (MPC) coupling with graphene nanosheets (GNP) was employed to solidify municipal solid waste incineration fly ashes (MSWI-FA) and stabilize the contaminants of heavy metals (HMs) and chloride salts in the matrix. The maximum compressive strength of 45.62 MPa and the minimum leaching concentration of 0.012, 0.0064, 0.00079, 0.0045, and 0.048 mg/L for Zn, Cu, Cd, Pb, and total Cr and 0.86 g/L for chloride were obtained from the GNP-MPC-MSWI-FA-cemented matrix in the orthogonal tests and toxicity-leaching experiments, respectively. MSWI-FA significantly changed the MPC hydration process. The influence of MPC on the speciation transformation of HMs was more prominent than that of GNP. Fick's theory model was appropriate in fitting the whole leaching process of HMs and dissolvable chloride species from the matrix under acid-immersion conditions. Both K-struvite and Phase-5 were formed in the matrix in mineral analysis, verifying the formation of both MPC and magnesium oxychloride cement (MOC). The chloride salts in the MSWI-FA facilitated the self-cementation of MOC from light-burnt magnesia in MPC. The mechanisms including the formation of phosphate precipitation, gelation encapsulation, and chemical hydration brought by MPC attributed to effective solidification/stabilization of HMs and chloride in the MSWI-FA.
危险品化学品经营许可证（带存储）