Effect of torsion loading on swelling in silica

Water reacting with silica causes the generation of hydroxyl SiOH accompanied by a volume or swelling expansion. The principle of LeChatelier ensures that the hydroxyl concentration increases with increasing externally applied stresses. From literature it becomes obvious that (a) the hydroxyl concentration must depend on the multi-axiality of the applied stresses, and (b) that the swelling effect is anisotropic. Based on Finite Element results it can be shown that for instance under torsion loading a strong stress-enhancement of the water/silica reaction with increased hydroxyl content must occur although this stress state shows a disappearing hydrostatic stress term. Due to the disappearing hydrostatic stress term under torsion loading, no mechanical effect would have been expected in torsion tests. Seen from this point of view, the torsion test seems ideal to us to provide evidence of anisotropic swelling. Further effects that can also influence the torsion test are addressed in the Appendix.