Articles written in Sadhana

    • Microstructure evolution of interface between magnesium ammonium phosphate cement and Portland cement under sulphate corrosion environment


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      This paper reports the test results on the bonding strength between magnesium ammonium phosphate cement and Portland cement. The bonded specimens were prepared by immersion in Na2SO4 solution. Following immersion, the surfaces and positions of fractures on the specimens were examined. SEM and an optical microscope were used to analyse changes of the interfacial microzone following different immersion periods. Microstructure changes of the magnesium ammonium phosphate cement-based interfacial microzone within the bonded mortar specimens were studied and compared with those immersed in normal conditions. The bonded mortar specimens were found to have weaker bonding strength than that of the mortar specimens in normal conditions. Under normal conditions, slight crystal morphology changes of the interfacial microzonewere observed and the crystal structure appeared compact, while more noticeable changes occurred within mortar specimens immersed in Na2SO4 solution, with the crystal structures within them being more loose. Thebonding behaviour of the magnesium ammonium phosphate cement includes mechanical bonding, mutual diffusion, and chemical bonding. Structural diagrams of the interfacial transition zone (ITZ) in different environments are also presented. Further investigations are needed to determine the performance of the bonding interface microzone of Portland cements and magnesium ammonium phosphate cements within repair materials in order to enhance the performance of cement-based composite materials for concrete repair.

    • Study on the hydration process and borax retarding mechanism of the magnesium ammonium phosphate cement-based coating system

      JUN LI

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      In this study, the reaction process of the MAPC coating system is investigated. And the delayed curing mechanism of borax in the coating hydration system is proposed. The results suggest that the research process of magnesium oxide-monoammonium phosphate-water diluted ternary suspension system is applicable for the MAPC coating reaction process, which can be divided into three stages: NH4H2PO4 dissolution, MgNH4PO4·6H2O primary crystallization and secondary crystallization. Borax can delay the setting and hardending time of MAPC, reduce the pH value and lower the hydration temperature without forming any new hydration product. Borax can improve the fluidity of MAPC coatings, and borax content has an effect on the compressive strength of MAPC hardened paste. The retarding effect is controlled by the formation and ruptureof the protective film on the surface of MgO; the other is controlled by lowering the system temperature and adjusting the pH value of the coatings. In the hydration process, borax does not form new hydration products.

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