期刊
CEMENT AND CONCRETE RESEARCH
卷 138, 期 -, 页码 -出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.cemconres.2020.106223
关键词
Magnesium ammonium phosphate cement (MAPC); Thermodynamic modeling; M/P molar ratio; Retarder; Assemblages of hydration products
资金
- National Natural Science Foundation of China [51878152, 51678219]
- Ministry of Science and Technology of the People's Republic of China 973 Project [2015CB655102]
Magnesium ammonium phosphate cement (MAPC) is commonly applied as a repair material. However, its hydration mechanism remains unclear. A thermodynamic modeling approach is employed to explore the hydration mechanism of MAPC. The results reveal that the hydration products of MAPC include (NH4)(2)Mg (PO4)(2)center dot 4H(2)O, MgHPO4 center dot 3H(2)O and MgNH4PO4 center dot 6H(2)O at 25 degrees C, 0.1 MPa, where both (NH4)(2)Mg(PO4)(2)center dot 4H(2)O and MgHPO4 center dot 3H(2)O are intermediate products that can transform into MgNH4PO4 center dot 6H(2)O with an increase in n(MgO)/n(NH4H2PO4) (M/P). The thermodynamic study of borax-modified and boric acid-modified MAPC indicates that the addition of boric acid does not change the assemblage of the hydration products; however, the addition of borax hinders the formation of MgHPO4 center dot 3H(2)O. According to the thermodynamic simulation, the lunebergite (Mg3B2(PO4)(2)(OH)(6)center dot 6H(2)O) phase, which is commonly thought to coat MgO to delay the hydration of modified MAPC, is not predicted to form. The addition of borax and boric acid can improve the final dissolution of MgO, promoting the formation of struvite.
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