In Africa, one of the most promising options for lowering costs and environmental impact of concrete is the use of limestone calcined clay cement (LC3) systems. However, improper use of the constituent materials may result in a concrete with substandard properties. The results reported here concern compressive strength, elastic modulus and drying shrinkage, and are part of a larger study on the properties of LC3 concrete made with African raw materials. Concrete with three different clinker levels and four different clays from South Africa and Tanzania were produced, which are compared with two reference mixes; one with 100% CEM II/A-L 52.5 N and the other with 50% of cement replaced by ground granulated blast-furnace slag. This paper concerns mechanical properties obtained on the various mix compositions. A second part to this publication, published in the following issue of CPI, will discuss relevant durability properties.