Carbonation-Induced Mineralogical Changes in Coal Mining Waste Blended Cement Pastes and Their Influence on Mechanical and Microporosity Properties

• Published in: Minerals (Basel) 2018-04, Vol.8 (4), p.169
• Main Authors: Frías, Moisés, de la Villa, Raquel, García, Rosario, Rodríguez, Olga, Fernández-Carrasco, Lucía, Martínez-Ramírez, Sagrario
• Format: Article
• Language: English
• Subjects: accelerated carbonation; Activated clay; Additives; Analytical methods; Aragonite; Assaigs de materials; blended cements; Calcite; Calcium; Calcium carbonate; Calcium carbonates; Calcium silicate hydrate; Carbon dioxide; Carbonates; Carbonation; Cement; Cement paste; Cements; Ciment pòrtland; Coal; Coal mining; coal mining waste; Compressive strength; Concrete; Decalcification; Enginyeria civil; Ettringite; Fourier transforms; Gels; Infrared spectroscopy; Kaolinite; Kinetics; Materials i estructures; Materials i estructures de formigó; Microporosity; Mine wastes; mineralogy; Phase composition; Pore size; Porosity; Portland cement; Pozzolans; Pozzuolanas; properties; Raman spectroscopy; Reaction kinetics; Size reduction; Testing; Àrees temàtiques de la UPC
• ISSN: 2075-163X; 2075-163X
• DOI: 10.3390/min8040169

The worldwide pursuit of new eco-efficient pozzolans is ongoing. Kaolinite-based waste is an eco-friendly source of recycled metakaolinite, a highly pozzolanic product. In this study, a blended cement paste containing 20% activated coal waste (ACW) was exposed to a 100% CO2 atmosphere at 65% RH for 7 days. The variations in its phase composition and strength were studied and compared to an OPC control. Both pastes were cured for 28 days prior to the carbonation test. Reaction kinetics were assessed using XRD, SEM/EDX, TG/DTG, FT-IR, Micro-Raman spectroscopy, pore solution pH and the cumulative carbonated fraction. The blended cement carbonated 68% faster than the control. While portlandite carbonation was the main reaction in both cements, decalcification was also observed (more intensely in the 20% ACW paste) in other hydraulic calcium phases (C-S-H gel, monocarboaluminate (C4AcH12), ettringite and tetracalcium aluminate (C4AH13). The end product of this reaction was calcium carbonate, mainly in the form of calcite, although traces of aragonite and amorphous carbonate were also detected. Compressive strength values rose with accelerated carbonation time and pore size reduction in both cement pastes.