Title:
Carbonated Fly Ash Alkali-Activated Aggregates: Properties, Performance, and Environmental Impact (Prepublished)
Author(s):
Mohd Hanifa, Usha Sharma, P.C. Thapliyal, and L.P. Singh
Publication:
Materials Journal
Volume:
Issue:
Appears on pages(s):
Keywords:
alkali activation; autoclave; carbonated aggregate; CO2 emission; concrete
DOI:
10.14359/51746810
Date:
5/8/2025
Abstract:
The production of carbonated aggregates from Class F fly ash (FA) is challenging due to its low calcium content, typically less than 10%. This study investigates the production of carbonated alkali-activated aggregates using FA and calcium carbide sludge (CCS). Sodium hydroxide was used as an activator and examined the effects of autoclave treatment on the properties of these aggregates. The optimal mixture, comprising 70% FA and 30% CCS, achieved a single aggregate strength of >5 MPa in autoclave carbonated (AC) aggregates, comparable to the strength obtained after 14 days of water curing in without autoclave carbonated (WAC) aggregates. Both AC and WAC aggregates exhibited a bulk density of 790 to 805 kg/m3 and CO2 uptake of 12.5% and 13.3% in AC and WAC aggregates, respectively. FE-SEM and FT-IR analysis indicated the formation C-A-S-H gel in noncarbonated aggregates, while calcite and vaterite, along with N-A-S-H gel, formed in carbonated aggregate. Concrete incorporating AC and WAC aggregates exhibit compressive strengths of 39 and 38 MPa, with concrete density of 2065 kg/m3 and 2085 kg/m3, respectively. Furthermore, AC and WAC aggregate concrete showed a reduction in CO2 emission of 18% and 31%, respectively, compared to autoclave noncarbonate (ANC) aggregate concrete. These findings highlight the potential of producing carbonated alkali-activated aggregates from FA and CCS as sustainable materials for construction applications.