Exploring the Modulation of Ternesite Performance Using Calcinated Metakaolin: Strength, Hydration, and Microstructure
摘要
Modulating ternesite hydration has become an urgent concern to improve cement performance. Herein, the ternesite was synthesized in laboratory and 5%–25% calcinated metakaolin (MK) was doped into ternesite Subsequently. The strength, hydration, and microstructure of the ternesite-metakaolin (T-MK) system were evaluated, and the related mechanism was explored via X-ray diffraction, isothermal calorimetry, thermogravimetry differential thermal analysis, the Brunauer-Emmett-Teller method, and scanning electron microscopy. MK accelerates ternesite hydration and shortens the induction period, with 20% MK exhibiting the optimum result. At 28 d, T-MK20 exhibits 16 MPa compressive strength and it is 5-fold higher than that of pure ternesite. T-MK20 exhibits a hydration degree of 48.4% at this age. In addition to C-S-H, gypsum, and Ca (OH)2, a new hydration product, ettringite, is generated in the hardened paste. The interwoven acicular ettringite crystals developes a mechanical skeleton, and then the C-S-H fills the pores to form a dense microstructure. Consequently, the hardened paste of T-MK exhibits good performance. These experimental results can open a new path for the application of low-carbon cementitious materials by incorporating ternesite.