THE MATERIAL CHARACTERIZATION OF MASONRY STONES AND MORTAR FROM THE ARCHEOLOGICAL SITE IN JERUSALEM

• I. Wasserman (National Building Research Institute, Technion, 32000, Haifa, Israel)

The antique masonry stones and mortars from the archeological site in Jerusalem were analyzed by chemical, mineralogical, physical and mechanical techniques in order to investigate the deterioration processes of materials. The investigated wall is a two-segment element, i.e.: an external wall of about 1.2 m width and the internal wall. The latter is dated to the Herodian period (c. the end of the 1st century BCE). There is no any data regarding the age of the external wall.

Strong decay and falling away of stones was observed at the upper part of the external wall in 1864⁽¹⁾. Thus, some restoration works of this part of the wall were carried out in the beginning of the 20th century. Strong swelling of the stones in the central part of the external wall appeared in the last few years.

Some cores were drilled in-situ from the central swelled part of the external wall and the laboratory samples were prepared. Cutting of the samples showed a difference in the hardness of the stones: the stones sliced from the most inner and the internal layers of the core (the level of about 0.8 up to 1.2 m from the outer surface of the external wall) were very soft. In spite of this, the stones cut from the outer layer of the core and from its skin (0 - 0.4 m from the surface of the wall) were distinctly tough.

The characterization methods used in the current investigation were X-ray fluorescence and diffraction, atomic absorption, petrographic microscopy, chemical composition analysis, testing of water absorption, rate of capillary rise and water de-sorption ability, micrometric measuring of stone's swelling under the continuous wetting, surface abrasion resistance and compressive strength at the dry and wet states.

It was fond that all the samples are very similar in their chemical composition. The main component of the stones and mortars is calcium carbonate. The negligible amounts of Na₂O + K₂O, SiO₂ and Cl- were observed. There was not fond any sufficient amount of Al₂O₃, MgO and Fe₂O₃, as well as there were not observed any organic impurities or harmful salts, as sulfates or nitrates. Thus, the presence of any clay minerals could be rejected. Water absorption of stones showed a similar trend with the hardness, i.e.: the inner layers of the investigated segment are characterizing by very quick capillary rise, i.e.: 60 - 100 mm per hour. However, the capillary rise of the stones from the outer and skin layers is more moderate: 15 - 25 mm per hour. Other tests are still in progress.

The results of the investigation are expected to explain the complex mechanism of materials' decay in the external wall and will allow predicting their future behavior, as well as a consistent approach to the wall conservation and repair could be achieved.

(1) Lue. T. Charles Willson. "The Ordnance Survey of Jerusalem (1864)". South Hempton, 1865.