Electro-Desalination of Sandstones With Cracks

Abstract

Historical stone monuments and buildings are lost due to salt induced decay. This paper deals with a method, electro-desalination (ED), in which an electric DC field is applied to the infected stones. The method utilizes that ions are transported (electromigrating) in the pore solution in the electric field. In the experimental work here, sandstone prisms were spiked with NaCl to high concentrations prior to ED. During the application of current, the Cl ions are electromigrating into a poultice at the anode, and Na ions into a poultice at the cathode. Damaged stones are often fragile and cracked, and the focus of this paper is to investigate experimentally if the salts are removed effectively from the stone parts next to a crack. In the lab experiments performed, a crack was cut half through the rectangular sandstone prisms perpendicular to the electric field. The results showed no delay on the ED processfrom the crack. All through the stone, very low concentrations of Na and Cl were reached. The concentration were even lower than the concentrations before the spiking. This finding of effective desalination around a crack is important, as it means that during ED, the poultice with electrodes can be placed around the cracked and fragile surfaces, and thus further damage from physical contact between poultice and fragile stone can be avoided.

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