Large-scale application of coal gasification slag in nonburnt bricks: Hydration characteristics and mechanism analysis

Abstract

Coal gasification slag (CGS) is a typical solid waste from the coal gasification process. Reusing CGS into building materials is a key means of realizing its large-scale utilization. This study aims to utilize CGS at a large dosage for the preparation of nonburnt bricks. The CGS, red mud, fly ash and desulfurization ash were utilized to synergistically prepare nonburnt bricks. The mechanical, durability and environmental performance of nonburnt bricks were analysed. Moreover, XRD, thermogravimetric analysis, FTIR, MIP and SEM were conducted to analyse the hydration products and microscopic morphology. The results revealed that when the CGS dosage reached 60%, the best performance of prepared nonburnt bricks was achieved. The unconfined compressive strength was 8.3 MPa at 3 d, 18.2 MPa at 7 d and 24.0 MPa at 28 d. Undergoing 25 cycles of freeze-thaw, the mass loss ratio was 0.9% and strength loss ratio was 10.67%. The alkaline solid wastes (red mud) have a promoting effect on the dissolution of active components in CGS, and the calcium content in blast furnace slag and desulfurization ash, as well as the sulfate in desulfurization ash, can enhance the formation of hydration products. The microstructures displayed the formed clustered C-S-H gels and reticulated C(N)-A-S-H gels tightly wrapped unreacted particles and filled the interstitial spaces of the materials, causing to an elevation in the compactness and a decline in the number of harmful pores. In addition, heavy metals (Cr, As, Cd and Pb) in CGS were well solidified. This study provides a rationale for the harmless and resourceful utilization of CGS.