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Concrete properties are dependent on many parameters such as ingredients, production and technology, construction methods and curing conditions that have made concrete as a complex and unpredictable material. But these are virtually ignorable against its precious advantageous and precise studies on above parameters may help us to produce concretes with our desirable properties. Ingredients are of those important parameters that play an essential role. Therefore it is seriously important to have enough knowledge about ingredients, their combined effects and interactions and also effects of their properties on concrete properties. Pozzolan materials can help us to achieve desirable characteristics of concrete and develop its mechanical and physical parameters, hence they are used widely. Improvement of mechanical parameters, permeability reduction, and durability increase are among their fabulous benefits of application. They are deemed as essential ingredients of high durable and strength concretes. Pozzolan weighted ratio is major parameters which develop a homogenous and united medium and improve the physical and mechanical parameters of concrete. The effects of pozzolan on physical and mechanical properties of concrete, moreover it’s specifications, depend on the parameters of other ingredients, such as type of aggregates, particle size distribution of aggregates, fineness modulus of fine aggregates, water-cement ratio, cement type and ect. Then study of combined effects of pozzolan specifications and parameters of other ingredients is inevitable for achieving to a concrete with ideal parameters. As we know, microsilica is the most popular pozzolan material which is used widely and it’s parameters and other ingredients parameters (such as type of aggregates, particle size distribution of aggregates, fineness modulus of fine aggregates, water-cement ratio, cement type and ect) have combined effects on the variation of concrete physical and mechanical parameters. So, in this study we selected microsilica as a pozzolan to determine the combined effects of its weighted ratio content, fineness modulus of fine aggregates and water-cement ratio on physical and mechanical properties of concrete. In this study, the combined effects of microsilica weighted ratio content, fineness modulus and water-cement ratio on physical and mechanical properties of concrete were investigated. For determination the effects of microsilica weighted ratio content on concrete parameters in different water-cement ratios and particle size distributions, 5 different microsilica weighted ratio contents, 3 water-cement ratios and 3 particle size distributions, were selected and totally 45 mix designs were prepared and subjected to slump test and compressive strength, tensile strength and modulus of elasticity tests. Obtained results show a direct relationship between microsilica weighted ratio content and physical and mechanical properties of concrete. Increase in microsilica content from 0% to 10 % in all water-cement ratios and fineness modulus, leads to slump decrease and mechanical parameters increase, while from 10 % to 20 % of microsilica content, mechanical properties fall down, but the reduction trend of slump continues. Also it can be seen that the effect of different weighted of microsilica, on physical and mechanical properties of concrete, reduces by increasing in water-cement ratio and intensifies with increment of fineness modulus of fine aggregates.

Keywords: microsilica, fineness modulus, water-cement ratio, concrete mechanical and physical properties

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