Storage and shelf life of unhydrated binders

The changes in cement characteristics due to prehydration affect the properties of mortars and concretes. Especially when admixtures and complex 

Concerning portland cement, the free lime is the phase most sensitive to moisture uptake (Dubina et al. 2011) see Table 1.1. As the water sorption starts at such a low relative humidity, the transformation of calcium oxide to portlandite cannot really be avoided in practise. Thus, the determination of free lime in clinkers and cements by quantitative XRD should always be verified by other methods, e.g. the extraction method of Franke (1941). From the cement clinker phases the orthorhombic C3A phase is the most sensitive to moisture. The prehydrated surfaces retard further hydration of the clinker grains (Dubina et al. 2011). Calcium silicates and calcium sulfates are involved as well in the prehydration process, as they may take up moisture already at quite low relative humidity. 

Due to prehydration issues and the related changes in cement and mortar properties, the shelf lives of cementitious binders and mortars in 

Cement constituent Relative humidity at which water sorption starts (%) 

Source Dubina, E, L. Wadso and J. Plank, Cement and Concrete Research, 41 (11), 1196-1204,2011. 

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