Page 272 - Handbook of Thermal Analysis of Construction Materials
P. 272
252 Chapter 6 - Retarding and Water Reducing Admixtures
In another example, conduction calorimetry was use to explain a
flash set in an oil cement slurry containing a lignosulfonate admixture. [22]
Conduction calorimetric curves were obtained for systems such as portland
cement, C A-gypsum-lime, and C AF-lime-gypsum systems containing
3 4
refined or unrefined lignosulfonates. The results showed that unrefined
lignosulfonate destabilizes the hydration process of the C AF-gypsum-
4
lime mixture causing a flash set. In the conduction calorimetry, the C AF-
4
10% gypsum-5% lime with 1–2% unrefined lignosulfonate (UL) dramati-
cally increases the intensity of the very early ettringite peak and reduces the
peak intensity for C S hydration at about 9–10 hours (Fig. 23). The
3
induction period is practically absent. It was concluded that the xylose
present in lignosulfonate was responsible for the flash set.
Figure 23. Effect of unrefined lignosulfonate on the hydration of C AF-10% gypsum- 5%
4
lime system.
10.0 READY-MIX CONCRETE
In ready-mix concrete trucks, the unused concrete is washed out
and this poses environmental, waste, and other problems. A novel approach
consists of adding a retarder-based admixture, such as carboxylic acid or
phosphorous-based organic acids and salts, to the concrete mix in the
truck. [35] This stabilizes the concrete from further hydration. When an
activator is added, subsequently normal hydration occurs.