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Weber, Johannes ao. Univ.-Prof. Dr.phil.

Hydraulicity in Ancient Mortars: Its Origin and Alteration Phenomena
conference proceedings
Other Natural Sciences, Archaeometry
Historical hydraulic mortars can comprise different reactive phases involved in the early- and mid-age development of binding properties such as pozzolana, brick powder or other reactive silica and alumina. However, the specific nature of the reactive phases in such binders is rarely clearly identified, particularly when different degradation or weathering patterns, frequently related to the carbonation of the binder, interact with dissolution and precipitation reactions. The question of which binder and aggregate components have contributed to the hydraulicity of a given historic mortar, a key to a better understanding of ancient technologies, is frequently not investigated in the case of mortars which underwent the above mentioned alteration processes. Microscopy provides a powerful analytical technique to determine the type of binders and differentiate between primary and alteration phenomena. By the example of three groups of binders, namely Roman opus caementitium/cocciopesto mortars from Ephesus (Asia Minor) and Vindobona (Roman Vienna), a 16th C. Ottoman horasan masonry mortar from Budapest, and 19th C. highly hydraulic lime filling mortars from Switzerland, the present article discusses two phenomena frequently observed when dealing with ancient hydraulic mortars: firstly as to the source(s) of hydraulicity of the mortar and secondly, that after a long period of time exposed to moist environments, the binder tends to present an inhomogeneous composition of an impure silica gel separated from calcium carbonate, accompanied by leaching and precipitation of binder constituents. These two phenomena are illustrated by polarized light microscopy (PLM) and scanning electron microscopy combined with energy-dispersive x-ray spectroscopy (SEM-EDX) and discussed in light of both conservation and understanding of ancient structures as well as how it can be applied to the current issues of alkali-aggregate reaction (AAR) and leaching in modern concretes.
Johannes Weber, A. Baragona, F. Pintér, C. Gosselin
Oguzhan Copuroglu
Delft University of Technology
Delft (Niederlande)
published in
Proc 15 EMABM, June 17-19, 2015, Delft