Physicochemical performance and hydration mechanism of alkali activated GGBS-steel slag-stockpiled CFB fly ash cementitious composites

Meng Gao, Mengying Li, Hang Jing*, Wei Sha, Jiahao Wang

*Corresponding author for this work

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Abstract

Steel slag (SS) and circulating fluidized bed fly ash (CFA) are the main by-products difficult to use among industrial solid waste due to their low reactivity and volume expansion. This work aims to develop a multi-solid waste eco-material, which is an alkali-activated cementitious composite (GSC) composed of ground granulated blast furnace slag (GGBS), steel slag powder (SP) and stockpiled circulating fluidized bed fly ash (SCFA) with stable working and mechanical properties. GSC was developed based on the synergistic hydration effect and the innovative curing method according to the characteristics of raw materials. The effects of curing humidity and SP-SCFA content on physicochemical properties and microstructure of GSC composites were studied, and the hydration mechanism of the above two factors in the system was revealed. The results show that gypsum dissolution of SCFA delayed the setting time in the system of GGBS: SP + SCFA= 60:40, SP-SCFA mass ratio of 1:1, and curing humidity of 45 % RH. The lower curing humidity effectively promotes the hydration of SP and SCFA and improves the compressive strength of GSC concrete (43.8 MPa at 28 days). CH crystals generated by SP and GGBS serve as nucleation sites to generate C-A-S-H gels. The ion dissolution of SCFA is accelerated, and then sodium rich N-(C)-A-S-H gel is formed. The amount of C-A-S-H and N-A-S-H gels produced is 45.8 % and 3.7 %, respectively. In addition, the release of sulfate from the gypsum in SCFA can promote gel formation and regulate the pH to control the hydration rate. The 45 %RH curing condition is beneficial for the water molecules and sulfate in SCFA to drive the migration of active ingredients, improving hydration rate and gel polymerization degree.

Original languageEnglish
Article number139635
Number of pages18
JournalConstruction and Building Materials
Volume458
Early online date24 Dec 2024
DOIs
Publication statusPublished - 10 Jan 2025

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This work is licensed under Queen’s Research Publications and Copyright Policy.

Keywords

  • Compressive strength
  • Hydration mechanism
  • Steel slag powder
  • Stockpiled circulating fluidized bed fly ash
  • Workability

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Building and Construction
  • General Materials Science

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