THERMAL ANALYSIS OF SUPERPLASTICIZERS

The physico-chemical phenomena associated with the setting of cement is complex. The time of setting is defined in ASTM in terms of the penetration of a needle to a specific depth. Ramachandranl l examined by DSC several cement samples containing water reducers, retarders, and superplasticizers that had just set. In all the mixes, an endothermal peak typical of Ca(OH)2 was detected, suggesting that at the time of set at least some CjS must hydrate. It was also observed that the superplasticized cement paste had hydrated to a lesser extent than the reference cement paste at the time of setting. This indicates that physical forces are also involved in the setting phenomenon. 

The analysis of superplasticizers is not easy as the manufactured product may not be pure. Techniques such as IR and UV spectroscopy yield useful, but not adequate, data so that analysis by other tools becomes necessary. Thermal analysis methods have been applied with some success to evaluate superplasticizers. The results could also be used for quality control purposes. 

Milestone l carried out DTA of superplasticizers and other admixtures in an atmosphere of oxygen and obtained several thermal inflections that could be used for differentiation of superplasticizers of similar or dissimilar types. In one example, two superplasticizers, thought to be identical, yielded different DTA patterns. In Fig. 20, two superplasticizers, apparently identical, show different patterns. 

DTG/TG has been used to differentiate various types of admixtures including superplasticizers.It was found that maximum weight loss occurred at 400°C for the sodium SMF admixture. Sodium SNF showed maximum weight loss at about 900°C. Six industrial superplasticizers (5 SNF and 1 SMF type) were subjected to DTG/TG investigations and thermal stabilities were found to be different so that the data could be used as finger prints for identification purposes. 

Evolved Gas Analysis (EGA) technique has also been applied to investigate superplasticizers.In this technique, the admixture is heated at a constant rate and the evolved gas, such as water, is measured. In water-containing compounds, water is adsorbed and measured coulometrically. In 

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