Synthesis and characterization of low-carbon cementitious materials from suspended calcined coal gangue

Abstract

Coal gangue is used to replace cement clinker to prepare cementitious material via activation techniques. Thus, the solid waste can be effectively disposed, and the carbon emission from cement production processes can be significantly reduced. In this paper, the product transformation, reaction mechanism, and thermal activation kinetics of coal gangue were analyzed by X-ray diffraction, thermal analysis, infrared analysis, and scanning electron microscopy. We employed a suspension calcination process to prepare high-activity metakaolin. A cementitious material was prepared from the metakaolin and cement, and the mechanical properties and hydration products were analyzed. The results show that metakaolin was formed by the dehydroxylation of kaolinite in the coal gangue during calcination, and the reaction was based on the Z–L–T three-dimensional diffusion mechanism with an activation energy of 190.2 kJ/mol. Metakaolin with dissolution rates of 69.5%–76.3% and 44.5%–52.3% of activated alumina and silica, respectively, were synthesized by calcining the coal gangue at 750°C–850°C for approximately 5 s via suspension calcination. The prepared cementitious material showed 28-days compressive strength of 57.5–61.5 MPa and an activity index of 114%–135%. The cementitious material participated in the hydration of cement and formed a structurally dense hardened body, which resulted in a high replacement volume and high strength of the specimens. The preparation of low-carbon cementitious materials by activating gangue via suspension calcination provides a basis for gangue utilization and reduction of carbon emissions during cement production.

Effect of adsorption interactions of Arabic gum with cement

“…Traditional concrete uses lots of cement and natural aggregates, which wastes energy and causes environmental problems [4]. As a result, many researchers have been developing novel approaches to incorporating a wide variety of industrial wastes into concrete, opening up a promising avenue for the potential use of wastes in the development of efficient concrete [5][6][7]. Although the use of fly ash (FA) as a replacement for cement has a favourable impact on the structure and mechanical characteristics of concrete, it has a significant adverse effect on the functionality of concrete in the early phases of its curing process.…”

Activation of Low-Quality Coal Gangue Using Suspension Calcination for the Preparation of High-Performance Low-Carbon Cementitious Materials: A Pilot Study

“…This strategy has been extensively researched by Scrivener and Dhandapani, who prepared a material with excellent properties by batching calcined clay with limestone powder and increasing blend content to 45 wt% [5]. Liu and Jiu et al prepared cementitious materials with superior properties using components such as desulfurized gypsum, limestone powder, and fly ash to activate calcined coal gangue [28,29]. Current research on coal gangue activation largely focuses on high-quality coal gangue, leaving the activation of low-quality coal gangue and its calcination products underexplored.…”

“…High-temperature calcination is the most effective method of coal gangue activation. During calcination, kaolin decomposes to metakaolin, which is responsible for the gelling activity of calcined coal gangue [7,9,11,29]. Moreover, calcination can effectively remove carbon from coal gangue, not only utilizing its energy but also eliminating its adverse effects on concrete, such as poor fluidity and additive consumption.…”

“…Moreover, calcination can effectively remove carbon from coal gangue, not only utilizing its energy but also eliminating its adverse effects on concrete, such as poor fluidity and additive consumption. Suspension calcination (a gas-solid system), a process recently applied to coal gangue activation, allows powders with particle sizes of ≤100 µm to be calcined in the form of a conveyor bed and offers the advantages of high efficiency, low energy consumption, and high product quality [12,29]. After more than 10 years of research, we have developed a pilot-scale suspension calcination system for the efficient activation of coal gangue and confirmed the effectiveness of this system for the activation of several types of high-quality coal gangue.…”

“…However, in-depth research on the applicability of our system to the activation of low-quality coal gangue is still lacking. According to previous studies, low-quality coal gangue is very different from highquality gangue in terms of composition, reaction characteristics and kinetics, the hydration mechanism of the corresponding cementitious materials, and product properties [16,[29][30][31]. Thus, the results of research on the suspension calcination of high-quality coal gangue and its conversion to cementitious materials cannot be directly applied to low-quality coal gangue.…”