Abstract
The hydration mechanism of ultra-high-performance cementitious materials (UHPC) departs considerably from that of normal cementitious materials (NC). In this study, the strength, isothermal calorimetry, chemical shrinkage, X-ray diffraction (XRD), and thermogravimetry (TG) methods are used to determine the hydration characteristics of UHPC and NC that contain silica fume (SF). A simple device was modified to test the chemical shrinkage for long-term growth, and the ultimate chemical shrinkage is obtained by semi-empirical formula fitting. It is found that the degree of hydration of UHPC is significantly lower than that of NC. The hydration kinetics analyzed using the Krstulovic-Dabic model shows that the hydration process of NC is type NG-I-D, which is characterized by gentle and prolonged hydration. However, the hydration of UHPC is type NG-D with the distinguishing features of early sufficiency and later stagnation. The growth of the strength, exothermic evolution, and phase development of UHPC is decelerated as the hydration process proceeds, which confirms the weak development tendency of hydration at the later stage. In addition, the effect of SF on the hydration of UHPC is minor, and the higher content of SF is beneficial to the hydration at the later stage.
Highlights
ultra-high-performance cementitious materials (UHPC) is an innovative cementitious material that possesses ultra-high mechanical properties and ultra-high durability and is generally prepared by the tightest accumulation classic theory [1,2,3].The compounding principle of UHPC makes it very different from traditional concrete in performance, and, in the final analysis, the hydration mechanism of the two systems is notably different.Up to now, three methods have been commonly used to study the hydration of cementitious materials [4,5,6], namely, the quantitative X-ray diffraction (QXRD) method, isothermal calorimetry, and chemical shrinkage test method
Three methods have been commonly used to study the hydration of cementitious materials [4,5,6], namely, the quantitative X-ray diffraction (QXRD) method, isothermal calorimetry, and chemical shrinkage test method
The Krstulovic-Dabic model with calorimetric data utilized by Yan [9] and Zhang [10] indicated that the hydration process of low w/b composites is significantly different with a high w/b cementitious system
Summary
Three methods have been commonly used to study the hydration of cementitious materials [4,5,6], namely, the quantitative X-ray diffraction (QXRD) method, isothermal calorimetry, and chemical shrinkage test method. Several studies have discussed the hydration process of cement by the above methods. Lam [7] and Huang [8] have identified that the composites with low w/b (
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