مرمت بقایای معماری بعد از کاوشهای باستانشناسی از مسائل مهم موردتوجه باستانشناسان و مرمتگران آثار تاریخی است، مواجهه آثار کاوش شده و از زیر خاک بیرون آمده با شرایط خرد اقلیم جدید ( که دارای نوسانات رطوبتی و برودتی متفاوتی از قبل است) موجب تغییر تعادل مصالح معماری و تخریب زودرس آن میگردد، این امر بهویژه در شمال و شمال غربی کشور باعث تسریع فرآیند تخریب آنها میگردد. ازجمله روشهای کاهش فرآیند تخریب ایزوله سازی بقایای معماری با ملاطهای سازگار باشد. در این تحقیق برای بهینهسازی ملاطهای پایه آهکی از پوزولانهای طبیعی شامل: خاکسترهای پوسته برنج، فضولات حیوانی و چوب استفاده گردید و از ترکیب این مواد با خمیر آهک 6 رده ملاطهای آهک -پوزولانی تهیه شد. در ادامه باهدف تعیین نمونه منتخب از لحاظ دوام و استقامت در مقابل چرخههای طبیعی، از آزمونهای پیرسازی تسریعی(شامل چرخههای تر و خشک شدن، حمله نمکها و چرخههای مبنی بر انجماد و یخ گشایی) و مقایسه خواص فیزیکی(چگالی، جذب آب ، تخلخل) برای کلیه ردههای ملاط استفاده گردید. نتایج نشان داد ملاطهای دارای پوزولان خاکستر فضولات حیوانی در مقابل چرخههای پیرسازی و سایر آزمایشهای فیزیکی مقاومت بهتری دارند؛ درنهایت با آنالیزهای XRD و XRF عناصر تشکیلدهنده پوزولانها و فازهای تشکیلشده در ملاط منتخب مشخص گردید.
عنوان مقاله [English]
Assessment of Lime-Based Mortars to Conservation of Architectural Remains from Archaeological Excavations
Next to the archaeological excavations, conservation and restoration of remains of monuments in the fields have received the attention of scientific archaeological excavations. Exposure of new finding materials to the microclimate conditions of earth surface causes to encourage their degradation process. Humidity and cryogenic fluctuations are the most important destructive factors for the architecture remains. Since a number of sites in the north and northwest of Iran encounter precipitation humidity and consequently the destruction of architecture remains, it appears that isolating outer remains of these structures using the compatible mortar is one of the best methods to reduce their damage. Lime mortar is appropriate for this purpose owing to its acceptable characteristics against the humidity. In this research, cow dung ash, rice husk ash and wood (with specific gradation) were used to optimize the lime mortar. The mix of these materials with lime paste prepared 6 different types of lime-pozzolan mortar. To determine the appropriate sample in terms of durability and consolidation against the natural cycles, accelerated aging tests including wetting and drying cycles, freezing & thawing and salt attack cycles as well as physical characteristics (densitometry, water absorption, and durability) for all types. The results of above processes indicated that the compositions of cow dung ash pozzolan’s have better resistance to the aging cycles and other physical experiments. Using XRD and XRF analyses, the structure and the amount of mineral phases were determined. Based on the results, it is recommended that lime mortar (optimized with cow dung ash) be used in the historic monuments and the humid climates of the north and northwest of Iran.
Conservation of the historical works while archeological excavations and the conservation, restoration, and maintenance of the obtained remnants in the excavation area, including tombs, architectural remnants, foundations, and even some of the ornaments after excavation are among the moral and professional principles of the scientific archeology.(Sease,1996) The necessity of the conservation of the archeological remnants in the recent century has been one of the most significant parts included in the macro planning of the archaeological approaches and cultural heritage-related knowledge. Among the measures taken for the conservation of the architectural clay and adobe remains after archaeological excavations are: 1) temporary conservation of the hills within the excavation times; 2) re-burial by re-filling the excavation area; 3) bricklaying and covering the walls and the remnants works in the area; 4) implementing roofs and shelters in the area for the temporary or permanent conservation; 5) using chemical and biological substances to strengthen the walls; 6) the use of geotextiles (permeable polymer textiles), and 7) coating the surface in the cold or humid regions.(Baghbanan et al, 2016; Rahmani,2006, Stanley Price,1999; Jandro et al 1999) Also, the northwest of Iran is among the rich regions of Iran in terms of archeology and tourism attractions, with an area of 7.2% out of the country's total area.(Negahban,1998) The northwest part of Iran is among the mountainous regions with a cold and dry climate in terms of climate conditions, causing the ancient sites to be severely damaged after archeological excavations. Therefore, it is necessary to prioritize compatible solutions in conservation measures. One of these measures is the use of protective mortars. The construction technology and mix design of this kind of mortars must be recognized to achieve the most efficient and stable formula; because it leads to the principled conservation in maintaining the obtained remnants in the ancient sites and saving the conservation costs in the future, in addition to achieving a mixture and processing methods and making the optimal mortar. (table 1)
How to use compatible mortars to protect architectural remains from archaeological excavations in the northwestern climate of Iran.What variable depends on the quality of compatible lime-based mortar with natural fillers? The protection of ancient sites after exploration in the northwestern climate can be done with compatible and eco-friendly calcareous mortar. The quality of lime-based mortar compatible with natural fillers depends on the high silica content of the filler.
Mortar Manufacturing: Lime was kept constant at 30%, and wood ash, rice husk, and animal waste were used as a pozzolan to mix the mortar filler to optimize the lime-based mortar. Six lime-based mortar mixtures with different amounts of rice husk ash (20, 35%), wood ash, and animal waste (10 and 35%) were used. 16 cubes were prepared from each mortar sample. Mortar samples were tested and analyzed to complete the setting reactions after 27 days from manufacture time. (Table 2). aboratory Studies: Laboratory studies include the determining examinations of the physical features of the samples (humidity percentage and water absorption, density, and porosity), (table.3) geological structure by determining the elements using X-Ray Fluorescence (XRF) analysis method, fuzzy determination using X-Ray Diffraction (XRD) analysis, and assessment of endurance properties based on the national and international standards(Table 7-8, Figures 10-11). The consecutive wetting and drying cycle, Freeze-Thaw cycle, the endurance against salt hydration cycle, mortar samples durability test.(Figure 1-3- 6-8 and Table.4-6).
After archeological excavations, the key issue of historical sites is increasing the humidity percentage and cold and heat fluctuations. As stated in the research literature, there are various solutions to reduce and manage humidity and cold fluctuations. In this study, using a durable and optimized mortar system ware studied to reduce the destructive effect of the above factors, especially in the northwestern region of the country. Accordingly, native and natural pozzolans were used to optimize the lime-based mortar. The applied pozzolans in this study include rice husk ashes, cow dung ash, and wood ash. According to the conducted studies, six different groups of mortar with different ratios were manufactured from the combination of three pozzolans along with sand and lime paste. Then, after 27 days to complete the mortar reaction, the proper samples were prepared for laboratory tests. These tests include accelerating aging methods (drying and wetting cycles, freeze-thaw cycle, and salt cycle) and the physical features (densitometry, porosimetry, water absorption, and durability (durability test)) implemented for all samples. The results of the examinations showed that the mortar with compounds and mix percentage (30% lime paste + 35% sand + 35% animal waste ash) has good resistance to aging, freezing and thawing cycles, and salt cycle. The selected sample showed satisfactory results after three durability cycles and was placed in a durable mortar class. Given the important role of grading in the durability and quality of the mortar, the results obtained from the grading diagram show that the pozzolan of the cow dung ash enjoys a proper grading than other pozzolans. According to the results of the above research, it is proposed that the pozzolan-lime mortars with the formula of 30% lime paste+ 35% sand+ 35% cow dung ash are used to overcome the descending humidity and environmental corrosion in the architectural remnants of the excavated historical sites in the cold climates, such as the ancient sites of the northwest of the country to evaluate the results in practice as well. The results indicate this mix's efficiency in the humid regions and salty regions near the wetting and drying cycles and freezing.
Mortar reversibility is another considerable point in using the coating mortars. Although reversibility is not entirely possible concerning some protective measures and materials, such as reinforcement and coating with polymeric materials in porous materials, the remarkable thing about applying mortars to protect the architectural remains from its archaeological excavations is that these mortars are suitable for reversibility. Their coating property depends on the depth of penetration of the mortar adhesive in the substrate and because this penetration is not very high (maximum 1 cm of slurry). Mortars use the substrate as a support in the coating state, and the principal setting occurs in the mortar and its components. Therefore, their function will be as a sacrificed layer in conservation. Based on the conditions of the studied mortars, in the case of proper monitoring and solving the critical causes of the destruction of the selected mortar, it seems that they will be efficient for at least five years. Finally, after the destruction process, their surface can be reconstructed, or the coating mortar can be implemented again.