Coal-derived char, due to its unique characteristics of lightweight, porous structure and carbon-rich material, has been recently investigated in different engineering applications. These investigations have yielded promising results, notably the high strength in coal char-based bricks containing 40% char by weight. However, the freeze-thaw durability of untreated char bricks with a higher char content (e.g., >40%) remains unsatisfactory, primarily due to the high water-holding capacity of char particles. The nanoparticles and fibers are conventionally used for improving the strength and durability properties of cement-based materials. Hence, considering the benefits of bricks with high char contents (e.g., lightweight and reduced cement usage), this study conducts a comprehensive investigation into the physical, thermal, mechanical, mineralogical, microstructural, and durability properties of lightweight char-based building bricks containing 50% char and 44% ordinary portland cement by weight. It also evaluates the effects of incorporating nano-silica, nano-alumina, carbon fiber, and glass fiber, as well as treatments with organic solvents (i.e., isopropyl alcohol and ethylene glycol), on the engineering performance of these char bricks. It is found that the highest compressive strengths are obtained at cubic samples with 2% w/w of nano-silica and 1% v/v of glass fiber, among various proportions of nanoparticles and fibers, respectively. The 28-day char bricks with 2% w/w of nano-silica exhibit the highest compressive strength (33.7 MPa) and Young’s modulus (103 GPa). Although the freeze-thaw durability improves for char bricks treated with isopropyl alcohol, only ethylene glycol treatment enables the char brick to pass the required 50 freeze-thaw cycles without a reduction in compressive strength. The results from this study demonstrate a promising potential for using coal char in the production of lightweight and durable building materials while minimizing environmental impacts associated with high cement usage and leveraging the advantageous properties of char.
Yu et al. (Sat,) studied this question.