Effect of Additives on Mechanical Strengths of Adobe Made From Soils of Isfahan

At present، there are still large numbers of existing buildings in Iran that are made of adobe. Isfahan is a historical city in Central Iran which enjoys the abundance of its historical and non-historical adobe buildings، some of which belong toseveral centuries ago. There are also many small villages inside and around Isfahan region that are totally made of adobe and accomodate tens of thousands of inhabitants. Recently، many researches have focused on improving the structural behaviour of adobe buildings، which includes enhancing mechanical properties of adobe units، and retrofitting and strengthening methods of existing adobe structures. In order to improve the mechanical properties of adobe made of soils in Isfahan region، used for restoration or reconstruction of the buildings، the effect of additives including sand، gypsum، lime، brick powder and straw with different amounts and were studied by planning 21 mix design schemes. After adding additives and making mix designs، the relevant mechanical tests were conducted. The obtained mechanical properties for every mix design were then compared with simple adobe (without additives). Soil used for making adobe is obtained from Habibabad region، North-east of Isfahan. The laboratory tests have been devided in two groups; The first group was considered the primary phase of the project، which consisted of the tests on plain soil including water content، grading، sedimentation، plastic limit، liquid limit and methylene blue tests. The second group or the second phase of the project was conducted on adobe samples and was comprised of compressive strength، flexural strength، abrasive strength and capillary absorption tests. The laboratory tests and relations used in this study have been applied according to the procedures suggested by Centre for the Development of Enterprise (CDE). Formulating the mix designs and laboratory tests on the designed samples were performed in the the soil and construction materials laboratory of the University of Isfahan during eight months. Obtained results indicate that gypsum or the combination of brick powder and gypsum are the best additives for adobe made from North-east Isfahan soil due to the resulting improvements in mechanical characteristics. The most appropriate mix ratios to be added to the plain soil are 25% gypsum of total weight or combination of 10% birck powder and 20% gypsum to be added to the soil. Lime as an additive has always played a negative role and reduces mechanical strengths of adobe، and therefore it is not recommended.