EVALUATION OF NANOLIME DISPERSIONS FOR THE PROTECTION OF ARCHAEOLOGICAL CLAY-BASED BUILDING MATERIALS

Clay-based building materials have been very popular in construction and common in cultural heritage sites around the Mediterranean. The excavation of the Late Bronze Age settlement of Thessaloniki Toumba (northern Greece), revealed an abundance of this type of material with apparent preservation problems mainly caused by swelling phenomena due to water absorption and/or humidity fluctuations. This led to the alteration of the structural and aesthetic integrity of the archaeological findings, jeopardizing the preser-vation of the site and as a consequence, the archaeological evidence that they contain. Triggered by the iden-tification of swelling clay phases in the sixteen samples of mud-bricks, this work studies the effectiveness, in terms of anti-swelling action, of two different categories of calcium hydroxide materials: saturated solution of calcium hydroxide (limewater) and various types of laboratory produced nano-lime dispersions. The ef-fect of the dispersion medium (water and mixed polar solvents) on the reactivity of calcium hydroxide with clays and the stabilization of their microstructure were investigated on laboratory produced clay briquettes containing different percentages of montmorillonite (1, 5 and 15 % w/w). The interpretation of mineralogical (XRD) and chemical results (FTIR) highlighted the significance of the dispersion medium for the treatments and the beneficial role of laboratory prepared nano-lime dispersions when they are used as swelling inhibitors. Nanolimes were able to react and stabilize the external layers of clays through the formation of C-S-H, thus resulting in increased durability of mud- briquettes against swell-ing.