The role of clay minerals in the deterioration of stone was the focus of two papers in yesterday’s session of the 12th International Congress on Deterioration and Conservation of Stone. Here are the highlights.

“Hydric Swelling of Clays in Brownstone” Timothy Wangler, Elaine Ngo, and George W. Scherer.

Timothy Wangler discussed how swelling pressures  of clay minerals could be measured in brownstone.  Two methods were used.  In the first laboratory method, brownstone was restrained between two platens then wetted.  The resulting swelling exerted measurable forces on the platen.   Alternately, a warping test was devised to again show the significance of clay swelling in stone deterioration.  Wet/dry cycles cause stresses from the swelling of clays which result in patterns like mud cracking or spalling. Wangler and his colleagues are now working on swelling inhibitor treatments for stone.

“Role of Swelling clay minerals in the spalling decay mechanism of the Pierre du midi Limestone (south east of France)” by Jeremie Berthonneau

In the second presentation, Jeremie Berthonneau shows that clay minerals can be present in limestone.  These clay minerals can exert swelling pressures that can lead to spalling and large losses of limestone.  He emphasizes the need to identify clay phases and understand their structure. Then he shows how X-ray diffraction and scanning electron microscopy can be used to study these clay minerals.  With regard to Pierre du midi limestone, Berthonneau shows that Smectitic layers enhance swelling and subsequent deterioration.

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