Assessment of meta-schist as a novel sustainable resource for Portland cement manufacturing

Abstract

In this study, the use of meta-schist as an alternative to sand-clay in preparing cement raw mixtures was investigated for the first time. Although there are high meta-schist reserves in many countries, especially in Turkey and America, there have not been enough experimental studies for their use in cement production, and their superior technical features still need to be demonstrated. To produce the highest quality Portland cement clinker by examining the mineral and chemical properties of meta-schists, two different raw meal samples were prepared, utilizing conventional cement clay as a baseline sample ((PC) Ref) and the other with meta-schist ((PC) MSC). The effects of both raw mixtures on burnability tests and reactivity were evaluated based on the unreacted lime content in samples after sintered at 1200, 1300, 1350, 1400, and 1450 °C. As a result of firing at 1450 °C, ((PC) MSC) exhibited good sintering properties by showing less than 1% free lime by weight. The porosity amount, distribution, grain structure of silicate phase crystals and equivalent crystal diameters and amounts of meta-schist clinker phases (C₃S, C₂S, C₃A and C₄AF) examined by polarizing optical microscope showed that they are suitable for the production of PC. The point counting method, Bogue model calculations, and XRD patterns have confirmed this result. The hydration products of the cement mortars were determined by SEM and EDX analysis at 2, 7, and 28 days. In addition, the compressive strength test results of ((PC) MSC) and ((PC) Ref) mortars after 28 days of curing ranged between 57 and 55,5 MPa, and the produced cement was classified as CEM I 42,5R.