An alternative raw material for Portland cement clinker preparation: Meta-schist

Abstract This study investigates the use of meta-schist as an alternative base material to cement clay in clinker production. First, the mineralogical differences between the reference cement clay, rich in silica but poor in iron and aluminium and the meta schist, rich in aluminium and iron and relatively poor in silica, were revealed by the XRD method. Two raw meal samples were prepared, one with ordinary raw materials (limestone and clay) ((RM)/Ref) and the other with meta-schist ((RM)/M) as a reference sample. The effects on the reactivity of the raw mix samples were evaluated on the basis of the unreacted lime content in the samples sintered at 1200, 1300, 1350, 1400 and 1450 °C. Then, two different clinker samples were produced by sintering the two raw mixtures at 1450°C. The relationships between the internal structures of the clinker samples determined by polarizing microscope (amount of porosity, distribution, grain structure of silicate phase crystals and variation of equivalent crystal diameters) were investigated. In addition, setting time, compressive strength and expandability properties of cement mortars produced with both clinker samples were tested. The microstructures of the mortar samples were examined on the 2nd, 7th and 28th days by scanning electron microscopy. It was observed that the meta-schist clinker contains less free CaO than the reference clinker at different temperatures. Both clinkers have similar proportions of alite and microstructures of alite and belite are identical in terms of crystal size and composition. At the same time, the distribution of the liquid phase is more uniform in the reference cement. Using meta-schist, low-temperature and low-cost Portland cement clinker can be produced without additional regulatory materials and blending.