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Earthen architecture is found all around the word and usage of building techniques. Architectural richness and various building cultures in it are noticeable. The broad and huge capacity of earthen architecture from the far past until today, have provided the ability for construction and building various types of bewailing's and shelters such as rural houses, palaces, religious building and etc. in the same way construction of complete city with earthen material. In this case, Iran is also considered one of the oldest countries which have used earthen architecture, the method which unfortunately has been forgotten for many years in contemporary architecture, and revival and recognition of it can provide us valuable lessons responding to our contemporary needs in the field of earthen architecture. Simple yet outwardly assumed banal techniques in traditional architecture could provide many technical and practical applications which could be studied and assessed further by the scholars. Therefore, a survey of these practical aspects of earthen structures, based on the local architectural know-how in the South of Khorasan, and their potential efficiencies in conservation and restoration of other earthen structures, is the focus of this paper. First and foremost, the main architectural resources in any region seem to be the local architects of these places. This is because the indigenous know-how of the local architects may lead them through the intricacies of the change in the used materials caused by the climatic and geological features regarding the constructional details. The problem is that as long as this local knowledge is not recorded anywhere except in the minds of the local architects, the general knowledge of this filed is gradually fading away and we seem to be moving towards losing this invaluable type of information. To deal with this problem this study intends to contribute to preserve parts of this knowledge and pass it forward through having had many of these local veteran architects directly interviewed. With this intention, through field studies some questionnaires were rectified and these survey forms have been given to eight of the most experienced local architects in this region. Analyzing the results of this study has been carried out within an applied-developmental research type relying on a combined method (descriptive, Geodesic, field research). Moreover, the contextual qualitative analysis of the results is presented as recommendations for conservation and restoration of earthen structures. It is valuable to say that these recommendations that have been presented here topically are in direct relationship with the result of interviews and the results are tried to classified and categorized in the fields of conservation and restorations. Eventually, according to the results, the lessons of vernacular architecture and important part of them such as experiences of traditional vernacular architects, have the capacity to be upgraded for contemporary restoration measures and can provide useful and practical recommendations that bringing them to attention will cause guaranty and live of restoration and conservation measures.

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Introduction: The use of earthen materials is common in hot and dry areas around the world, due to a cheap, abundant and easy access to materials. Today, the use of earthen materials is common in urban and rural areas in developing countries. In Iran earthen materials have partly shaped our architectural culture and identity. Kahgel is one of the oldest traditional plastering and mortars in Iran, which has been used to insulate the roof and facades of buildings from moisture and rainfall. Although the importance of processing and curing mortars and plasters is well known among architecture and building professionals and builders, no research has been conducted on the effect of processing time upon the physical quality and mechanical properties of traditional mortars, especially Kahgel. The main purpose of this study is to evaluate the importance and duration of curing process on the physical and mechanical properties of Kahgel using experimental methods.

Material and methods: As the first step, soil samples were taken from different areas of Isfahan and then these samples were examined using different experimental methods. Then the most appropriate soil sample in terms of physical and mechanical properties was selected. Several samples of Kahgel mortars were produced using the selected soil sample and different percentages of straw fibers. For these kahgel samples the compressive strength, tensile strength, linear shrinkage and cracking were measured to determine the most appropriate combination of selected soil mixed with straw fibers. In the second phase of the study, the type of soil and straw percentage were not changed, while the processing time was considered as an independent variable. The new Kahgel samples were prepared by a variety of processing time and then their compressive strength and tensile strength were measured to examine the effect of the curing time on the mechanical properties of Kahgel.

Results: The results indicate that the compressive strength dropped with increasing straw fiber content and increased with increasing soil content. The results of all the tests indicate that tensile strength of Kahgel increased with increasing straw fiber content up to 6 %, but the higher straw contents decreased tensile strength. The linear shrinkage of samples decreased with increasing straw fiber content. The results showed that the curing time of Kahgel affects its mechanical properties, especially compressive strength and tensile strength. Therefore, the mechanical properties of Kahgel can be improved by increasing the duration of curing time.

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