Carbonation and Leaching Behaviors of Cement-Free Monoliths Based on High-Sulfur Fly Ashes with the Incorporation of Amorphous Calcium Aluminate

Mustafa Cem Usta; Can Rüstü Yörük; Mai Uibu; Reiner Traksmaa; Tiina Hain; Andre Gregor; Andres Trikkel

doi:10.1021/acsomega.3c03286

Carbonation and Leaching Behaviors of Cement-Free Monoliths Based on High-Sulfur Fly Ashes with the Incorporation of Amorphous Calcium Aluminate

ACS Omega. 2023 Jul 31;8(32):29543-29557. doi: 10.1021/acsomega.3c03286. eCollection 2023 Aug 15.

Authors

Mustafa Cem Usta¹, Can Rüstü Yörük¹, Mai Uibu¹, Reiner Traksmaa², Tiina Hain³, Andre Gregor¹, Andres Trikkel¹

Affiliations

¹ Department of Materials and Environmental Technology, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia.
² Department of Mechanical and Industrial Engineering, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia.
³ Department of Civil Engineering and Architecture, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia.

Abstract

The high sulfate content in various alkaline wastes, including those from fossil fuel and biomass combustion, and other industrial processes, necessitates careful management when used in cementitious systems to prevent potential deterioration of construction materials and environmental safety concerns. This study explores the under-researched area of high-sulfur fly ash (HSFA) utilization in the production of cement-free monoliths through accelerated carbonation and further examines the effect of niobium slag (NS)-a calcium aluminate-containing slag-as an additive on the strength development and the mobility of SO₄^2-. The methodology involves mineralogical and microstructural analyses of monoliths before and after carbonation, accounting for the effects of accelerated carbonation treatment and NS addition. The findings suggest that accelerated carbonation significantly improves the initial compressive strength of the HSFA monoliths and generally immobilizes heavy metals, while the effect on sulfate immobilization can vary depending on the ash composition. Moreover, the addition of NS further enhances strength without substantially hindering CO₂ uptake, while reducing the leaching values, particularly of sulfates and heavy metals. These findings suggest that it is feasible to use calcium aluminate-containing NS in HSFA-based carbonated monoliths to immobilize sulfates without compromising the strength development derived from carbonation. This research contributes to the understanding of how accelerated carbonation and NS addition can enhance the performance of HSFA-based materials, providing valuable insights for the development of sustainable construction materials.