O. Hadad - Department of Civil Engineering, Mahabad Branch, Islamic Azad University, Mahabad, Iran
O. Soltani - Department of Civil Engineering, Bonab Branch, Islamic Azad University, Bonab, Iran
H. Azizian - Department of Civil Engineering, Mahabad Branch, Islamic Azad University, Mahabad, Iran
V. Mam Ghaderi - Department of Civil Engineering, Urmia University, Urmia, Iran

Due to the increasing use of concrete, researchers and engineers are constantly tried to improve its mechanical and physical properties as well as its efficiency. Hence, they have made use of the most diverse products and the most modern concere technologies. In the present study, oak bark ash and macro fly ash have been used as the most widely used pozzolans in the concrete industry. The parameters of concrete and the percentages of materials used in its structure remained constant, but different percentages of oak bark ash and macro fly ash have been added to the mix design. Brazilian method and bending strength of concrete was applied. The parameters of concrete density, concrete consistency, compressive strength, and tensile strength have been investigated..Therefore, the existing materials required necessary tests; based on obtained resulted, an optimal design for the concrete mix was introduced from which the necessary specimens were taken into consideration. Then, oak bark ash was used as an additive, in proportions of ۰.۲ and ۰.۴% by the total weight of cement, and macro fly ash was used to replace cement as a variable in various proportions of ۵, ۱۰, ۱۵ and ۲۰% by total weight of cement. Based on the existing variables and the control design, a total of ۱۵ groups of mix designs were introduced. The statistical population includes ۴۵ cubic specimens (۱۵×۱۵×۱۵), and ۴۵ cylindrical specimens (۱۵×۳۰) for tensile strength test using Brazilian method. Also ۴۵ bending beam specimens having dimensions of ۱۰×۱۰×۵۰ were examined. Finally, after analysis of the obtained results, we dentified the superior mix design had the best performance and that both additives affected all studied parameters, including concrete consistency, density, compressive strength, tensile strength, and bending strength of concrete. However, macro fly ash had a great effect on the conrete strength. The obtained results also indicated that excessive use of any additive could have adverse effects on the mechanical properties of the concrete.

bending strength, Compressive strength, Macro fly ash, Oak bark ash, tensile strength