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Hydration of sodium phosphate-modified high alumina cement

Published online by Cambridge University Press:  03 March 2011

Weiping Ma  and
Paul W. Brown
Weiping Ma
Affiliation:
Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802-4801
Paul W. Brown
Affiliation:
Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802-4801
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Abstract

High strength can be achieved in high alumina cement (HAC) through the incorporation of phosphate-based additions at levels of 10 and 20 wt. %. In order to establish the mechanism that results in higher strength, the effects of a variety of condensed sodium phosphates (NaPO3)n, (NaPO3)n · Na2O, Na5P3O10, and (NaPO3)3 were studied. The influence of these additions on the kinetics of hydration was studied using isothermal calorimetry. The phosphatic additions enhanced reactivity, but x-ray diffraction analyses did not reveal evidence of new crystalline phosphate-containing hydration products. Microstructural evolution was examined in real time using environmental SEM, and hydration products exhibiting distinct morphologies were observed. The features exhibited ranged from amorphic to polygonal shapes, plates, and fibers. These frequently formed between crystalline calcium aluminate hydrate grains and by doing so appear to provide a means to enhance the strengths of these cements. In spite of the morphological variations, companion energy dispersive x-ray analysis showed that the compositions of these products did not vary widely. Their ranges of compositions are 52-60 wt. % Al2O3, 20-26 wt. % P2O5, and 20-24 wt. % CaO.

Type
Articles
Information
Journal of Materials Research , Volume 9 , Issue 5 , May 1994 , pp. 1291 - 1298
Copyright
Copyright © Materials Research Society 1994

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