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influenced by temperature. On the other hands, the existing of carbonate as one of the major components of clayey soils in arid and semi-arid lands, and its effect on engineering properties of the soils prove the necessity to study the simultaneous influence of carbonate and temperature on the engineering behavior of clayey soils. In the present work, the interaction between clay and carbonate in high temperatures has been investigated. Bentonite were mixed with different percentages of carbonate and sand. The variations of added carbonate were 0% (natural carbonate content), 10%, 20%, and 30%, respectively, and added sand were 20% and 40%. The soil samples were carefully mixed with enough water to bring them to their plastic limit and were kept in plastic bag for uniform-moisture distribution for a period of 24 h. It was then sieved through a #10 mesh to ensure to achieve a uniform mixture. Samples for testing were then prepared by compacting soil mixtures into cylinder mold in three layers. The test specimen dimensions were 35 mm in diameter and 70 mm in height. The clay specimens were allowed to air dry at room temperature for 24 h. Bentonite specimens were kept in plastic bag to prevent development of cracks during air drying due to high crack potential. The samples were then oven dried at 110 °C for a period of 24 h. The test specimens were heated to temperatures of 300, 500, 700, 900 and 1100 °C, using programmable Carbolite electric furnace. The specimens were placed in the electric furnace at room temperature and then the temperature was increased at a rate of 3 °C/min until the desired temperature was reached. Once the treatment temperature was reached, it was held at that stage for 2 h, then the furnace was turned off. The specimens were then allowed to cool overnight in the closed furnace. After this curing condition, samples with different levels of temperature including 25 °C (laboratory temperature), 110, 300, 500, 700, 900 and 1100 °C were used for experiments. The changes of physical and engineering properties of the soil were studied by performing macro-structural tests such as linear shrinkage, water absorption and unconfined compression. The results show that as temperature increases close to the de-hydroxylation temperature, strength gradually increases. At de-hydroxylation temperature, the strength significantly increases, so that the strength of bentonite specimens increases 3 to 4 times. The strength of bentonite specimens significantly decreased with increasing the heat over de-hydroxylation temperature. This strength reduction was due to the formation of microscopic voids and pores in the specimen. Analyzing the simultaneous influence of carbonate percentage and heating indicate that the increase of carbonate percentage in a given temperature results in the decrease of strength and the amount of this reduction is different in different temperatures. In bentonite specimens, heating causes the water absorption to be decreased, however, the increase of carbonate percentage results in the increase of water absorption in a given temperature. Temperature, Bentonite, Calcium carbonate, water absorption, Unconfined compressive strength.

Keywords: temperature, Bentonite, Calcium carbonate, Water Absorption, Unconfined compressive strength

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