Progressive weakening of zeolite granules due to cyclic moisture loading and unloading

• Increasing moisture content decreases the mechanical properties of the granules.
• Moisture loading–unloading cycles represent an extreme conditioning.
• An increasing number of moisture loading–unloading cycles decrease the strength.
• All granules exhibit a brittle fracture.

The influence of moisture content and cyclic moisture loading and unloading on the mechanical properties like the strength of three different types of zeolite granules has been studied by uniaxial compression tests. The tested granules had been processed using different contents of binder and different thermal drying/activation temperatures. A moistening–drying cycle consists of moistening the granules in a climate chamber using wet air and complete immersion in a water bath followed by thermal drying in a drying chamber at 350–400 °C. The experimentally recorded force–displacement curves and digital images of the granule and fracture surfaces recorded using scanning electron microscopy are evaluated and discussed.With increasing number of moistening–drying cycles, a continuous decrease in the strength of granules take place due to non-regenerative damage of the structure. However, a critically constant strength level is more or less reached after ten cycles.

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