Effectiveness of Hydroxyapatite in Preventing Salt Damage in Weathered Limestone

Abstract

Every day, the limestone that comprises statues, buildings, and monuments around the world are deteriorating as a result of exposure to the elements. Consolidants have been found to successfully restore much of the mechanical integrity of these stones, but salt damage continues to be an issue. This paper explores the use of Hydroxyapatite (HAP), a successful limestone consolidant formed from the reaction of calcite with diammonium hydrogen phosphate (DAP), in preventing salt scaling in limestone. This is accomplished by treating limestone samples with DAP and subjecting them to a series to wetting/drying cycles, during which they are impregnated with sodium sulfate solution and subsequently dried. This paper also studies the effect of the DAP treatment and the salt damage on the sorptivity of the stone. TAP is explored as an alternate consolidation treatment through solitary tests and side-­‐by-­‐side comparison tests with DAP.