Synthesis and characterization of sustainable eco-friendly unburned bricks from slate tailings

The volume of tailings in the world has increased rapidly in recent years, which poses a substantial ecological threat. With the objective of reducing negative impacts on environment and reuse the abandoned slate tailings, the possibility of making eco-friendly unburned bricks by using slate tailings from Shaanxi Province of China was investigated. Raw materials included slate tailings, fly ash and cement, and bricks were produced through the process of mixing, molding, and curing. The optimal compressive strength of the product was found at the slate tailings: fly ash: cement = 5:2:3 (wt.%) with 7-day curing at room temperature and 1-day curing in oven, and the forming water content is 15 wt.%. Under these conditions, the compressive strength and water absorption rate were 26 MPa and 14.32% respectively. Other physical properties and durability conform to the Chinese GB/T4111-2013 standard for test methods for concrete blocks and bricks and the Chinese JC/T422-2007 standard for unfired bricks made of tailings. In addition, a variety of methods were combined to explore the formation mechanism. The phase composition, chemical structure and microstructure of the brick are analyzed by XRD, SEM and AFM. Finally, molecular dynamics (MD) was used to simulate main cementation component, the hydrated calcium silicate (C-S-H) gel, to advance the understanding of mechanical properties of brick at the nanoscale. The results show that the C-S-H gel formed in the curing process acted as the main adhesive component, and the slate tailings are mainly worked as aggregate skeleton to provide support strength for unburned bricks. (C) 2021 The Author(s). Published by Elsevier B.V.