Abstract
In the oilfield industry, the retarders are used to delay the setting time of cement to meet the requirement of pumping process. The effect of 1-hydroxyethane-1, 1-diphosphonic acid (HEDP) on the hydration of ordinary Portland cement was investigated in this study. Isothermal calorimeter was used to analyze the retardation effect of HEDP on cement hydration, and the hydration products were studied by Thermogravimetry–differential thermal analysis, Fourier transform infrared spectroscopic, X-ray diffraction, and Scanning electron microscopy, respectively. The results showed that HEDP in cement induced the longer induction time, because the nucleation and growth of calcium silicate hydrate were poisoned by HEDP. While HEDP favored gypsum consumption and ettringite formation at early ages of cement hydration due to the generation of Ca-HEDP complex, and SEM images showed that a change in the morphology was found from a fiber-like structure to a unique microvilli-like structure of C-S-H. However, HEDP did not negatively affect the degree of hydration. Retarding mechanism of HEDP on the cement hydration was consistent with the “dissolution-precipitation” theory.
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