With the development of infrastructure all over the world, the demand for cementitious materials is increasing. Despite the improvement of the cement production process, a significant amount of CO 2 is released into the environment. The use of supplementary cementitious materials (SCM) to replace part of the clinker in cement is a solution for reducing CO 2 emissions into the environment, while maintaining the same mechanical and durable properties of concrete. The quantities of SCMs, which have been used the most, are not sufficient for the growing needs of the cement industry. Clays containing kaolinite are available in countries where the greatest need for cement is expected. By calcination it achieves pozzolanic properties and in combination with limestone it reduces production costs and negative impact on the environment. In this research, part of the cement has been replaced by a combination of calcined clay and limestone. Tests of concrete of target strengths C25/30 and C30/37 were performed. The properties of fresh and hardened mixtures were examined. It is possible to achieve the required properties of ordinary strength concrete by addition of calcined clay and limestone with a reduction of negative impact on the environment.