Development of high-strength and durable coal char-based building bricks

Abstract

Pyrolysis coal char is a byproduct of the coal industry and causes undesirable environmental issues from conventional coal combustion and gasification. This paper presents a novel approach to utilize coal char for manufacturing new and environmentally friendly building bricks. The effects of sand, silica fume (SF), superplasticizer (SP), air-entraining admixture (AE), and graphene oxide (GO) on the properties of char-based bricks, including heat of hydration, thermogravimetric and differential thermal analysis, microstructures, density, and compressive strength, are investigated. A new treatment method using hydrophobic liquid in a vacuum condition is proposed to improve the durability of char bricks, which is evaluated based on water absorption and freeze-thaw (F-T) cycles. The experimental results indicate that the new bricks with 40% char content have a good compressive strength performance of 49.2–52.5 MPa, which compares favorably to conventional clay bricks with compressive strength of 10–20 MPa. Adding AE and GO slightly increases and decreases the compressive strength at 28 days, respectively. Moreover, the proposed treatment method significantly improves the durability of char bricks. The treated char bricks exhibit a boiling water absorption of ≤2.3%, which is 90% lower than that of untreated char bricks. The untreated and treated char bricks can achieve 22 and 120 F-T cycles, respectively. Overall, this study presents a promising approach to repurpose coal char and produce sustainable building bricks with high compressive strength and durability.