Page 260 - Handbook of Thermal Analysis of Construction Materials

242 Chapter 6 - Retarding and Water Reducing Admixtures

Figure 14. Calorimetric curves showing the effect of phosphonic acid on the rate of
hydration of tricalcium silicate.

Phosphonic acid had a retarding effect on C A hydration (Fig. 15).
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The reference C A produced the maximum heat effect at 3.6 minutes with
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a value of 113.7 cals/g/h. At an addition of 0.03% acid, the peak occurred
at 19.2 minutes producing 76 cals/g/h.
DSC investigations showed that the addition of phosphonic acid to
the C A + gypsum mixture, in the presence of water, retards the hydration
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and inter-conversions in the system. [31]