STONE RESTORATION part 3

STONE RESTORATION PRACTICE IN PALESTINIAN TERRITORIES:

A CASE STUDY FROM JERUSALEM

part 3

LABORATORY EXPERIMENTS

The aim of the laboratory experiments, which were conducted in the laboratories of the Department of Civil Engineering at Birzeit University, was to determine the density and the optimum absorption ratio which would cause all components used in the restoration process– existing on-site building stones; new stones imported from different sites and the materials mixed- for binding, patching/filling and sealing of masonry– to all interact with and complement each other. The following experiments were conducted:

-          Porosity test for: stones in use in existing buildings and for the new stones to be used in restoration obtained from the local quarries.

-          Sieve analysis of the crushed stone and the silica sand that will be used for preparing the various mixtures for lab testing.

-          Porosity test of a variety of mixtures (crushed stone, silica sand, hydrated lime, hydraulic lime and white cement), to be used in further testing. The introduction of the white cement into the laboratory experiments is done just because it was used in the restoration of most of buildings mentioned beforehand in this paper and in order to test the impact of this material within the locally prevailing restoration’s practice.

The above-mentioned experiments were conducted using material samples that were selected as follows:

-          Stone pieces extracted from the buildings inside the Old City of Jerusalem, and from the several quarries that provided and still presently provide stones for the restoration activity in Jerusalem.

-          Silica sand, which is usually brought by trucks from the Palestinian coast in Gaza or from Israeli sites like Ashdod, Askelon and Dimona. Lab tests conducted by the Geotechnical and Material Testing Center (GMT) in Ramallah/ Palestinian Territories, over the past five years have demonstrated that this sand has a light salt content as well as organic impurities. Still, the present practice is to soak the sand in water and wash it carefully before using it in the restoration process.

-          Crushed limestone, which is crushed in special stone crushers. The crushed stone available on the local market contains a high percentage of fine particles, however, exceeding the percentage permitted nationally and internationally. To remedy this, a visit to the crushed stone manufacturers in Al-Ram (a village north of Jerusalem) allowed the researchers to obtain a more appropriate sample with a lower percentage of fine particles. This was achieved by extracting the sample at the stage in the production cycle before the final sieve. It is worthy to notice, that this material was the major component of the oldest hand-mixtures used for building construction purposes in Palestine till the introduction of the concrete technology in the first half of the twentieth century.

-          Hydrated lime, available on the local market in the form of 25kg bags, and still widely used in the restoration process and is prepared for use by soaking it in water for at least three days.

-          Hydraulic lime, available recently on the local market in the form of 25kg bags (NLH 3.5), and gradually is being used in the restoration process. 

-          White cement, available on the local market in the form of 50kg bags. Recently, this material is still added rather in various amounts to make the mixtures dry faster.

Porosity Test of the Stones

The laboratory tests started with the assessment of the density (dry & bulk) and the optimum absorption ratio of the stone samples extracted from different sites in the Old City of Jerusalem (Table 1), as well as for stone samples from several quarries that provided in the past and still provide stones for the restoration activity in the city (Table 2).  These quarries are at A’nata, a village near Jerusalem famous for its ka’kooli limestone (medium soft stone), at Birzeit, and at the various locations in Hebron, Bethlehem, Beit Fajjar and  the Jordan Valley, which stones were used and are used extensively at the present time by most of the local institutions working on rehabilitation of Jerusalem structures. All samples were cut on a stone-cutting saw and fashioned into cubes of uniform dimensions in order to simplify the testing procedure. Porosity was measured through the void spaces in each sample, and is presented as a fraction of the volume of voids over the total volume:

n= (Vv/VT) *100=VT-Vs /VT) 100

Where Vv is the volume of voids, VT is the total volume and Vs is the volume of the solid parts.

The results obtained from the stone porosity tests, shown in Tables (1 & 2), reveal that the water absorption ratio for the stone samples from the Old City varies between 3.99% and 10.38%. These ratios are significantly higher than the measurements for the newly-quarried stones from Birzeit (0.74%- 1.05%), Hebron (0.74-1.07%), Bethlehem (0.98- 1.09), Beit Fajjar (1.75-1.86%), and the Jordan Valley (0.79%), which, as mentioned, are extensively used in the current restorations in the Old City of Jerusalem.  By contrast, the A’nata quarried samples show a ratio of (14.91-16.74%), which is higher than this ratio for the existing stones in the Jerusalem old structures. As for the density, the results in Tables (1 & 2) also disclose that this density for the stone samples from the Old City varies between 1.81 and 2.33g/cm³. All these density values shown in Table (2) are lower than the measurements for the newly-quarried stones from Birzeit (2.66- 2.69 g/cm³⁾, Hebron (2.63-2.70 g/cm³), Bethlehem (2.70- 2.72 g/cm³), Beit Fajjar (2.57-2.59 g/cm³), and the Jordan Valley (1.97 g/cm³), while the A’nata quarried samples show a density of (2.00-2.03g/cm³), which is compatible with the average density of the existing stones in the Jerusalem old structures (2.08 g/cm³).

Comparing all these ratios with the results in Tables (7 to 9) will show that it is possible to determine the porosity of the stones in an old building being subjected to restoration, for the purpose of defining both the appropriate stone material- in terms of absorption ratio and density- to be used in replacement of deteriorating stones, and for defining the location from which to obtain the stone to be crushed and used in the preparation of the hand-made mixture, suitable for each case of restoration, considering that the  deteriorative effects differ from one place to another, from one building to another, and even from one facade of a single building to another, according to the stone’s origin and its ability to resist against the different deteriorative factors.

....to be continue....