Admixtures are natural and manufactured chemicals which are added to the concrete before and during mixing. The most frequently used admixtures are air- entraining agents, water reducers, water-reducing retarders and accelerators. Admixtures are used to give special properties to new and hardened concrete. Admixtures may enhance the durability, workability and strength characteristics of a given concrete mixture. Admixtures are used to overcome difficult construction situations such as cold and hot weather placements, early strength requirements, pumping requirements and very low water cement ratio conditions.