In this investigation, four blended cement pastes were made from Portland cement and limestone by using the suitable water of consistency of each paste. The influence of limestone replacement was studied through the determination of non-evaporable water content, free lime content, total porosity, compressive strength and pH value for each blended cement paste. The blended cements were compared with the ordinary Portland cement. The pH values increase with the increase of limestone addition as well as with curing tlme. Also, the addition of limestone enhances the rate of hydration as measured from the combined water contents. In the light the results obtained, blended cement pastes and mortars can be made by the addition of limestone up to 20% giving reasonable mechanical properties and suitable passivation of reinforcing steel in the concrete.
