One of the most important environmental issues around the world is the disposal of waste materials. Accumulation of used tires has always has always been a major concern ,because they are not easily biodegradable even after a long time if buried. Therefore, recycling or using them in the industry always has been important. Usually, in concrete, about 20 to 30% of its volume, depending on the proportion of the mixture, consists of fine aggregates. Considering the high annual production of concrete, even if a small percentage of natural aggregate is replaced with worn rubber crumb, it leads to a significant saving of natural resources. As a result, over the years, researchers have tried to use different recycled materials at different levels. On the other hand, used tires are produced from used tires in the automotive industry, which is growing rapidly in different parts of the world. As a result, the use of these tires in concrete is in line with sustainable development. On the other hand, studies have shown that the use of rubber in concrete causes a decrease in mechanical characteristics such as compressive strength, flexural strength and modulus of elasticity. One of the effective ways to compensate for this reduction is the use of silica fume in concrete. In this research, the behavior of structural elements with different percentages of rubber in self-compacting concrete has been studied. Also, the effect of using microsilica in compensating the reduction of mechanical characteristics has been eva‎luated. First, the frequency and damping modes resulting from free vibration and also the flexural behavior of self-dense reinforced concrete beams have been investigated. In beam samples, ductility and damping have increased with increasing rubber percentage. The eva‎luation results of concrete containing microsilica have shown that the use of microsilica in the amount of 20% has caused the weakness of the samples in compressive strength and flexural behavior to be adjusted to some extent. Also, reduction of compressive strength, flexural strength, natural frequency, reduction of maximum load bearing, first crack load, increase of crack width opening and increase of deformability index have been observed. So that with the increase of crumb rubber up to 30%, 116% increase in damping, 23% decrease in the natural frequency of the first mode, 32% increase in ductility index, 24% decrease in the maximum flexural load beams have been observed. The failure mode in the samples containing a high percentage of rubber was flexural-shear failure, but in the samples with low rubber, the failure was mainly flexural.

پيام اسدي، محمدرضا افتخار

مريم داعي، نيما نور محمدي