Utilization of extracted carbonaceous shale waste in eco-friendly cementitious blends

Abstract

This research concerns the analysis and application of extracted shale from mining waste at the Lubelski Węgiel „Bogdanka“ S.A. coal mine in Poland. Various analyses were performed on both raw and thermally activated forms of extracted shale, and then the thermally activated one was used as a partial cement substitute in a PC-based paste. In order to reduce the required additional energy, the activation temperature for the extracted shale was chosen to be 600 °C according to the simultaneous thermal analysis measurement. Chemical, mineralogical, physical, and morphological analyses, thermogravimetry, and pozzolanic activity tests of raw and thermally activated extracted shale were conducted. The Portland cement pastes containing either 10 wt%, 15 wt%, or 20 wt% of thermally activated extracted shale were compared to a reference plain cement paste. Cement pastes with the thermally activated extracted shale were studied in the fresh and also hardened state after 7, 28, and 90 days of setting. Furthermore, mechanical, structural, and microstructural properties were measured and compared with the reference. Simultaneous thermal analysis with a mass spectrometer (STA-MS), isothermal calorimetry, X-ray powder diffraction (XRD), and strength activity index (SAI) evaluation were used to assess the evolution and rate of the pozzolanic reaction. All the performed analyses confirmed the pozzolanic activity of the thermally treated extracted shale and its potential in cement industry applications. The extracted shale also acted partially as a microfiller. The use of calcined extracted shale reduced the porosity of the cement matrix and increased its flexural and compressive strength. For 90-day samples, a slight hindrance in the precipitation of final substances was observed as a result of different kinetics of hydration and pozzolanic reactions. Taking all of the results into consideration, the coal mining waste – calcined extracted shale – can find use as a partial cementitious substitute for up to 20 wt%.