Supplementary Cementing Materials and Other Additions

These materials are known by various names. The European concrete standards refer to them as additions.I The ASTM classifies them as mineral admixtures. In the literature, they are also described as supplementary cementing materials, cement replacement materials, or 

The main methods of investigating the effect of supplementary materials and other additions on cement hydration include XRD, SEM, NMR, Mossbauer spectroscopy, IR, and thermal analysis. Poorly crystallized products that form in these materials are advantageously investigated by TG, DTG, DTA, DSC, and conduction calorimetry. Thermal methods have also been suggested for characterization of the supplementary and other materials. 

Hydration of fly ash cement differs from pure cement in terms of the hydration rates of the clinker phases, amount of calcium hydroxide formed, composition of the clinker hydration products, and additional hydration products from the reaction of the fly ash.I l Lower amounts of lime are formed in the presence of fly ash because ofthe pozzolanic reaction between the fly ash and lime formed in cement hydration. Fly ash generally retards the reaction of alite in the early stages and accelerates the middle stage reaction. The accelerated reaction is attributed to the existence of nucleation sites on fly ash particles. The aluminate and ferrite phases hydrate more rapidly in the presence of fly ash, and also there is a significant difference in the hydration rate of the belite phase up to 28 days. Table 1 gives the relative hydration rates of cement compounds in the presence of fly ash as derived from conduction calorimetry. [ 1 It can be seen that the earlier rates of hydration are generally retarded, and the later stage hydration rates are accelerated. 

Synthesized Compounds or Clinker Minerals Early Stage Hydration I II III Later Stage Hydration 

R = Some fly ashes having high Ca adsorption capacity and high pozzolanic activity will accelerate the hydration at these stages 

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