**Roman Jaskulski 1,\*, Daria Józwiak-Nied ´ ´ zwiedzka 2and Yaroslav Yakymechko <sup>1</sup>**


Received: 3 October 2020; Accepted: 21 October 2020; Published: 23 October 2020

**Abstract:** Calcined clays are the only potential materials available in large quantities to meet the requirements of eco-efficient cement-based materials by reducing the clinker content in blended cements or reducing the cement content in concrete. More than 200 recent research papers on the idea of replacing Portland cement with large amounts of calcined clay are presented and discussed in detail. First, the fundamental information about the properties and structure of clay minerals is described. Then, the process of activation and hydration of clays is discussed, including the methods of pozzolanic activity assessment. Additionally, various testing methods of clays from different worldwide deposits are presented. The application of calcined clay in cement and concrete technology is then introduced. A separate chapter is devoted to lime calcined clay cement. Then an influence of calcined clay on durability of concrete is summarized. Finally, conclusions are formulated.

**Keywords:** calcined clay; binder; supplementary cementitious materials; cement-based materials
