Stability of Treatment from Earth-Based Mortar in Conservation of Stone Structures in Tanais, Russia

Identification of materials, masonry elements, their shapes, physical and mechanical parameters and type of connection is crucial for the conservation works related to ancient masonry structures. In the case of the archaeological site where the research was carried out (Tanais in Russia), some irregular masonries made of limestone and earth-based mortar were stated. Such type of structures is a common finding during the archaeological excavations in the Black Sea basin carried out by the Division of Fundamental of Building of the Civil Engineering Faculty of the Warsaw University of Technology in cooperation with the Institute of Archaeology of the University of Warsaw and the Antiquity in Southeastern Europe Research Center. The structure of such walls is degraded to a large extent, has low strength, internal cohesion and, as a result—low durability. At the same time, due to their historical importance, proper conservation, as well as the development of the whole methodology for selecting the best composition of earth-based mortar, is of great importance. Presented in the article, research on earth-based mortars were carried out to determine the best way to strengthen them, using cement (creating an earth-based mortar stabilized with cement with the most appropriate recipe) and other substances available in the region where conservation works are carried out not only to improve the durability physical and mechanical parameters but also to achieve the desired esthetic effect in the form of a suitable tone together with the compatibility of repair mortar with the substrate and constitutes the primary stage of creating the whole methodology of selecting a proper composition of earth-based mortar for the conservation of ancient stone structures. In this stage, four criteria were taken into consideration: mechanical (compressive strength test), conservation (compatibility, reversibility, color, texture and surface profile), durability (freeze–thaw test, the appropriate finish of the surface, shrinkage, workability) and technological one (application of materials, technology and techniques available at the conservation area). Applied treatment was evaluated in the next two years of the conservation works. Parameters of repair earth-based mortar stabilized with cement fulfilled all of the above-mentioned requirements.