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This paper is the first part of a research project which was supported by TUBITAK titled “Determination of Optimum Limestone Content in Portland Limestone Cement Production from the View Point of Mechanical Performance and Sulfate Originated Durability Problems”. In this stage, blended cements incorporating different amounts of limestone powders from 5 to 40% were prepared. The problems observed in the preparation stage of limestone blended cements and the effects of limestone replacement on the physical and mechanical properties were investigated. Increasing of limestone replacement ratios resulted in a wider particle size distribution. In contrast with the increases in Blaine values, fineness (residue at 32 µm) values of cements have also increased. Mortars had a sticky and cohesive consistency. Also, increasing the limestone incorporation caused decreases in unit weights and compressive strength values of mortars with a parallel increase in water absorption values at all ages.