This ensures that the concrete does not set too quickly before it can be placed in its final position or too slowly so as to hold up construction. Types of Cements The code gives five groups of cements, all of which are mixtures of different proportions of clinker and another major constituent. The five groups are: 1. CEM I Portland cement: This comprises mainly ground clinker and up to 5% of minor additional constituents. 2. CEM II Portland composite cement: This comprises of seven types which contain clinker and up to 35% of another single constituent.