This investigation is on alternative cementitious materials of low cost, energy and environmental emissions. Portland cement (PC) was replaced by different types of calcium sulphate (hemihydrate HH, or anhydrite AN), fly ash (PFA) and cupola slag (CS) from an iron foundry. Pastes of blends of (HH or AN) – CS – PC and (HH or AN) – PFA – PC were characterized. The compositions varied within the ranges of 0 – 35% PC, 15 – 80% HH or AN, 10 – 80% CS and 10 – 80% PFA. The water/solids ratio was kept at 0.45 for HH blends and 0.37 for those of AN. The pastes were cured in dry and for some time under water. Selected blends of CS were repeated with blast furnace slag (BFS) for comparison. CS showed better results over PFA and less than BFS, perhaps as derived from its chemical composition, phase configuration and physical characteristics. These and other results of microstructural characterization will be discussed. This work is part of a broader research on the development of alternative environment friendly hydraulic composite cements of Portland cement highly replaced by calcium sulphate and industrial byproducts.