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Thursday, 18 July 2019
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Raw materials & technologies, Raw materials

Dynamic retarder exchange triggers Portland cement hydration

Monday, 19 May 2014

A series of NMR and isothermal calorimetry tests were conducted to depict a retarder exchange mechanism.

One result is that the precipitated calcium phosphonate got easier dissolved Source: Evonik

One result is that the precipitated calcium phosphonate got easier dissolved Source: Evonik

For their study the researchers replaced a powerful organophosphonate retarder (nitrilotris(methylene) triphosphonate, or NTMP) by a much weaker phosphate retarder (sodium hexametaphosphate, or SHMP). The retardation of cement hydration by NTMP is believed to be primarily attributed to the dissolution of calcium from the cement and the subsequent precipitation of a layered calcium phosphonate that binds to the surface of the cement grains and strongly inhibits further hydration.

SHMP removes strong retardation effect of NTMP

The test results show that the addition of SHMP helps to dissolve the precipitated calcium phosphonate and thus removes the strong retardation effect of NTMP. The proposed retarder exchange mechanism may be employed to develop cement systems with a controlled setting behaviour.

The study is published in: Cement and Concrete Research, Volume 63, September 2014, Pages 20-28.

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