Prehydration of Clinker minerals can occur due to the following:

1. As a result of poor drying in the mill, the cement produced would still contain a high moisture content.
2. When there is insufficient gypsum dehydration in the mill, and the cement temperature entering the storage silo is too high.
3. When cement is exposed to humidy.

Cement prehydration can result in significant strength loss of the final product. To determine the impact of cement prehydration, if any, the Loss On Ignition (LOI) of a cement sample can be used.

The following procedure must be followed:
A 200 g sample of cement must be taken from the silo discharge. The sample must be heated to 70°C and held at this temperature for 2 hours, after which the sample must be weighed to determine the LOI at this temperature. The same sample must then be heated to 140°C and held at this temperature for 2 hours, before being weighed to determine the LOI at this temperature. The same sample must then be heated to 450° and held at this temperature for 2 hours, before being weighed to determine the LOI at this temperature.

The LOI determined at each temperature must then be entered in the input cells and submitted. Based on this data, a report will be submitted to you indicating whether any adverse affects on the cement strength can be expected due to prehydration.