The DOE method, used by Firstmix, incorporates empirical data, which relate concrete strength to the free water/cement ratio and the coarse aggregate type for concrete made from different cements.
The DOE method includes information on the strength, which will typically be obtained by concrete made with three types of cement commonly used in the UK, Ordinary Portland cement (OPC), Sulphate-resisting Portland cement (SRPC) and Rapid hardening Portland cement (RHPC), conforming to BS 12 or BS 4027, see References 3 & 4. The concrete strength data for these three types of cement is incorporated in three standard cement files, which are issued with Firstmix.
The Cement Properties Dialog allows you to load the properties of a cement type into the Mix Design form and to edit the properties of an existing cement type to create a new cement type. You should do this if none of the standard cement files match the strengths attained by concrete made with the cement types you use.