Table 2. See Table 3. Wetting and Drying Test: Studies of the wetting of walls show that there is appreciable non-uniformity of wetting and confirm what is often noticed when buildings are wetted by rain: that much more intense wetting usually occurs near the top of walls than at lower levels.
Differences in wetting are attributable to the wind-flow patterns over the wall surface, which direct the paths of the falling raindrops Ritchie The rain that falls on the masonry walls of Qusayr Amra has three possible paths of penetration: through the body of the unit; through the body of the mortar; and through openings between the unit and the mortar.
However, the amount of water that penetrates the mortar does not contribute significantly to a leakage problem. Staining and efflorescence on masonry walls reflect the patterns of the wetting and the manner in which water runs over and off the wall surface. The water flow patterns may also produce stains and streaks by eroding the masonry material, the resulting differences in texture and color giving an appearance of vertical streaks on the wall surface.
On the other hand, decay due to freezing is a serious consequence of the wetting of masonry. Experiments have shown that damage done to masonry materials by freezing depends in large measure on their moisture content when the materials are frozen Ritchie In our study, 15 cycles of wetting and drying were carried out on three limestone samples from Qusayr Amra. Based on the findings of the current test, shown in Table 4, it can be stated that the Qusayr Amra stone building materials are relatively sound and the minor loss could be related to the salt content of the building and not to rock main components.
Table 4. The water dissolves salts in the masonry, forming solutions that subsequently move to the surface where the water evaporates, depositing the salts. The salts may have originated within the masonry units or the mortar, but the latter is a particularly important source. Efflorescence frequently reflects the direction of wetting walls. Efflorescence also reflects differences in the amount of wetting received by a wall; it often appears at the top of the wall but not at the bottom Ritchie The rate of chemical reaction between the stone surface and acid rain depends mainly on several catalytic metal ions Penkett et al.
Finally this salt penetrates into stone pore spaces and crystallizes there, leading to crystallization processes over years, and then breaks the stone surfaces. This phenomenon depends essentially on the amount of salt present, its nature and the number of dry-wet cycles Binda and Baronio The results are shown in Tables 4, 5 and 6.
The weathered rocks have lower Na2O compared to fresh rocks. This suggests that the Na is also mobile during weathering. Duzgoren-Aydin et al. This may be due to the high absorption rate of the weathered rocks. These tuffs also have soft cement between the particles. The density of the fresh rocks is higher than that of weathered samples, indicating the higher durability of the fresh rocks. Table 5. In other words, the relationship between the content, types and distribution of soluble salts and the surrounding environmental conditions was not adequately explained.
The determination of the hydrothermal conditions that control the behavior of single salts is a straightforward process Benavente Each single salt has its specific equilibrium relative humidity ERH at a certain temperature and remains in solution when the surrounding relative humidity is higher than this ERH, but crystallizes when the surrounding relative humidity is lower than this ERH. Following these observations, it might be assumed that salt damage could be avoided in a very straightforward way by controlling the surrounding relative humidity and temperature.
Unfortunately, the reality is more complicated, mainly because contamination with single salts in porous materials is rare Price , while predicting the behaviour of a salt mixture is much more complicated. Many models have been presented in an attempt to understand the behaviour of mixed salt solutions. See Figure 5 and 6. The use of the Pitzer model in preventive conservation studies Steiger and Dannecker and Steiger and Zeunet led to the creation of an expert chemical model ECOS for determining the environmental conditions needed to prevent salt damage in porous materials Price The Runsalt program, which is a graphical user interface to the ECOS thermodynamic model, will be used to study the salt composition and behaviour of selected samples from Qusayr Amra.
The two results for cations and anions from the sampling points 5, , and cm were chosen to evaluate the thermodynamic of the soluble salts at Qusayr Amra. The Runsalt program requires the input of three types of data: cation and anion content with the average of one environmental parameter temperature or relative humidity and the range of fluctuation of the other parameter temperature or relative humidity.
The literature review of the Runsalt applications showed that temperature did not significantly affect the behavior of the salt solution, while relative humidity had the greatest impact. A simple natural shelter Tress Shelter could be used to avoid these dangerous ranges. Figure 3. Thermodynamic analysis using Runsalt. Crystallisation sequence of soluble salts: relative humidity against amount of substance mol.
Sampling number LQA August After the removal of Gypsum Figure 5. Relative humidity and temperature readings from the data logger. Location: Qusayr Amra. Recorded period August Dangerous relative humidity ranges, safe relative humidity ranges and relatively safe relative humidity ranges for the soluble salt content in the tested samples from Qusayr Amra.
To achieve this goal data from laser scanning and digital imagery was combined. In this project, a laser scanner is used in order to collect thousands of 3D points every second at high levels of accuracy and to precisely digitize complicated objects.
The system is able to measure points per second. Because it is not possible to have complete 3D coverage for outdoor complex-structured sites based on data collected from a single station, different viewpoints have to be used to resolve the occlusion, as depicted in Figure 7. The Mensi system captures a calibrated video snapshot of x pixel resolution, which is automatically mapped onto the corresponding point measurements, as depicted in Figure 8.
These low resolution images are not sufficient for the high quality texturing that is desired for documentation, monitoring and material visual analysis.
For this reason, additional images were collected with the Canon D camera, which provides a resolution of x pixels with a focal length of 20 mm. These images depicted in the bottom row of Figure 7 were collected at almost the same time and have more texture details, as can be depicted in Figure 9.
Figure 9. The evaluation of all previous results and their consequences can be summarized in the following points: 1. The calcareous nature of the Qusayr Amra stone building materials and its porosity ratios as well as the fine pore structures are very dangerous rock features for decay mechanisms, especially salt damage. However, the open porosity results could be seen as an advantage in the case of applying certain adhesives to the monument to increase its stability; however these adhesives should be applied after the removal of salts and in low concentration in order to fit the fine pore system of the building materials.
The soluble salt results shows that the Qusayr Amra stone building is relatively high in salt content, particularly at the lower and middle parts of the building. These readings suggest strongly that the groundwater is the main source of soluble salts at the site.
The landscape features around the site support this potential source of the soluble salts since the building is located in the center of a shallow depression. A simple moisture test carried out at the site by weighing three samples from three different levels before and after drying strongly support the idea of groundwater as a main source of moisture and therefore the potential soluble salt source. A detailed groundwater evaluation in the area is needed to compare salt types in this water and salts at the building.
The detailed microclimate evaluation of the site accompanied by the thermodynamic calculation of the movements of soluble salts showed that salt crystallization could be avoided at the site by a slight modification of the current environment, especially the relative humidity ranges at the site.
Natural shelters, such as trees, or built shelters appear to be the priority for preventive measures. Although the authors are totally aware that these measures could be difficult to implement, both for practical and aesthetic reasons, they still seem vital for the long-term conservation plan of the site. Conclusion Salt crystallization is the most powerful weathering agent for rocks. During salt crystallization, pressure crystallization occurs within the pores of rocks, and the degree of weathering depends on the degree of salt saturation of the solution and the pore size.
The stone conservation principles that must be adopted in Qusayr Amra should be appropriate for the original building technology, partly to preserve the integrity of the original design but also for practical reasons. The results discussed above showed that the total salts soluble in tested samples are generally low.
However, calcium and sodium are the main cations, and chloride, nitrate, sulfate and phosphate are the main anions. The total soluble salts are slightly higher at the lower levels of the building. This may suggest that the most likely source of the salts in the building is due to groundwater; the fieldwork investigation showed that an artificial water well is part of this Umayyad bath at a distance of about five meters, where a large amount of water has accumulated that could result in raising the groundwater level and thereby the amount of total soluble salts in the building.
Analytical work should commence with the consideration of the building stonework, since the occurrence of salt is related to specific deterioration phenomena and to particular microclimates, as well as hydrological conditions. However, except for the physical and mechanical tests, deterioration and weathering morphologies should be also mapped by visual inspection.
This is an important step, since these morphologies are considered an effect of stone alteration and weathering processes. A detailed visual inspection at Qusayr Amra should be carried out for the stone deterioration in relationship with the four orientations.
References - Al-Asad, M. The Umayyads. The Rise of Islamic Art. Vienna , pp. Painting technique and state of conservation of wall paintings at Qusayr Amra. Deterioration of porous materials due to salt crystallization under different thermohygrometric conditions. Activity coefficient in natural waters.
In Pitzer, K. Clegg or P. Allan, J. Aldershot: Scholar Press, pp. Modelling of sulphur dioxide deposition on the Bern sandstone. Preservation and Conservation of Cultural Heritage.
Lausanne, pp. Geomechanical and geochemical changes during early stages of weathering of Karamu Basalt, New Zealand. Pore properties as indicators of breakdown mechanisms in experimentally weathered limestone. Earth Surface Processes and Landforms. Pore size distribution and the durability of a porous limestone.
Quarterly Journal of Engineering Geology. Brice and Eggleton, A. Atmosphere Environment Thermodynamics of electrolytes, I.
Theoretical basis and equations. Journal of Physical Chemistry The Mechanical properties of a material are those which affect the mechanical strength and ability of a material to be molded in a suitable shape. Such property of material from which if we pull it and leave it, then it will come back in its shape again, it is called Elasticity.
This property is useful for materials used in tools and machines. Such a property of material from which if we pull but it cannot regain its original position when leaving it, then it is called plasticity. Eg: This property of the material is compulsory for forgings, in stamping images on coins and ornamental work. Such property of a material that we can pull and make it into long wire form, we call it Ductility.
A ductile material needs to both strong and plastic. The ductile material used in mild steel, copper, aluminum, nickel, zinc, tin, and lead.
If we beat any metal that causes it to spread and form into a sheet form, So we call this property Malleability. A malleable material needs to be plastic but it is not essential to be strong. Malleable material is used in engineering practice is lead, soft steel.
Suppose there is a metal and we have to scratch it, The harder the scratch is, the harder our material will be considered. Suppose we have a material called iron and on the other side is silver aluminum So if we impact on both, the highest impact will be on aluminum because it is a weak metal and its hardness is less. But if we talk about iron, It will be more difficult to scratch on the sheet of iron if we compare it with aluminum, so hardness will be more of iron. So a hard material that we cannot easily scratch, is equally hard.
Material that if we bend or twist, how much energy can absorb before it breaks is called Toughness. The toughness of the material has been decreased when it is heated. So Toughness is properties that provide information about the capacity to absorb maximum energy.
In this, we suddenly impact and check how much energy is absorbed at that time. It has a pendulum that suddenly attacks the material, and connects its maximum energy absorbing capacity. Suppose we have a material and we impact it and it should be broken, without deform is called Brittleness. Or If we pull such a material, it breaks instead of pulling it, we call it Brittleness.
Cast iron is a brittle material. Such material on which we apply pressure, bend, and pull, but do not break it in that condition is called Tenacity. When a material loads more than a specific load, then there is a chance of failure But in fatigue, Any material fails even at low load if we apply a repetitive load. This failure is known as fatigue. Fatigue value is many times less than that stress, in which a material has to fail in actual.
The factor of fatigue on materials: Less strength, life, and Durability. Fatigue property is used for observing In designing shafts, connecting rod, springs, gears, etc. Causes of fatigue in the material : 1. Dynamic forces 2. In spite of repetitive loads on a material, it is not broken then it is its fatigue property.
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