Publication: Electroprecipitation of Magnesium and Calcium Compounds for Weathering Protection of Ornamental Rocks
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2020-01-01
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Abstract
Electroprecipitation can be considered as a novel consolidation technique that can
compete with commercial consolidation treatments since, it allows to reduce its
accessible porosity, both superficially and in-depth; increasing considerably its
mechanical properties and precipitating a compound chemically compatible with the
material to be treated. The purpose of this study is to assess the effectiveness of the
electroprecipitation of four different inorganic compounds constituted by Magnesium
and Calcium Carbonate, Calcium Phosphate and Calcium Oxalate, in 6 cm thick
specimens of quartz-arenite. The suitability of the treatment was assessed in samples
treated and aged for 4 years under environmental conditions, comparing the changes
caused in: structural properties (measuring the ultrasonic pulse velocity, anisotropy,
tortuosity, pore size distribution, and mercury accessible porosity), mechanical
properties (superficial hardness, uniaxial compressive strength and drilling resistance)
and aesthetic properties (color). In addition, the morphology and composition of the
compound precipitated were assessed by XRD and SEM-EDX. This study found that
the precipitation of the insoluble compounds by this technique: I) takes place in a
homogeneous way, reducing the anisotropy of the material and its tortuosity, which
increases the durability of the material against the action of external agents, such as
water, soluble salts, and pollutants. II) Increases the mechanical properties and causes a
considerable increase in the ultrasonic wave transmission. III) Allows filling almost
completely the pores where it precipitates, which reduces the damage risk caused by
crystallization pressures. IV) Under these treatment conditions (environmental
conditions, confined space and forced precipitation by an electric field), the precipitated
phases were: Magnesite, Hydromagnesite, Calcite, Hydroxyapatite, and Wewhellite.
However, the color changes detected indicate that it is necessary to carry out previous
studies in the laboratory to reduce this aesthetic problem, before applying it on site on a
certain material, especially in heritage constructions.