Efflorescence mitigation in construction and demolition waste (CDW) based geopolymer. (15th October 2022)

• Record Type: Journal Article
• Authors: Tan, Jiawei; Cizer, Özlem; Vandevyvere, Brecht; De Vlieger, Jentel; Dan, Hancheng; Li, Jiabin
• Is Part Of: Journal of building engineering. Volume 58(2022)
• Publication Date: 2022-10-15
• Subjects: Construction and demolition waste (CDW) -- Geopolymer -- Efflorescence -- Metakaolin (MK) -- Ground granulated blast furnace slag (GGBS); Building -- Periodicals; 690.05
• DOI: 10.1016/j.jobe.2022.105001
• Languages: English
• ISSNs: 2352-7102

Abstract

Abstract: Using construction and demolition waste (CDW) as a raw material in geopolymer synthesis is gaining a growing interest owing to the dwindling availability of traditional aluminosilicate sources. However, CDW-based geopolymer (CDWG) is more prone to efflorescence due to the relatively low reactivity of CDW. Up till now, the efflorescence mitigation in CDWG has not been well documented. This study compared the effect of Al-rich admixtures, i.e., metakaolin (MK), and Ca-rich admixtures, i.e., ground granulated blast furnace slag (GGBS), on the efflorescence mitigation in CDWG. Results showed that both MK and GGBS addition significantly reduced the efflorescence formation of CDWG, but were based on different mechanisms. MK addition significantly decreased the number of excessive alkalis (from 24.5 to 10.2 mol%) through Al species introduction and N-A-S-H gels formation. Although GGBS addition only marginally reduced the excessive alkalis (from 24.5 to 19.9 mol%), it reduced the porosity and capillary water absorption of the geopolymer samples through C-A-S-H gels formation, hereby impeding the migration of alkalis and reducing the efflorescence extent. However, considering the risk of crystallization pressure and cracks induced by internal efflorescence in GGBS-containing samples, adding Al-rich materials (e.g., MK) is a better choice to mitigate efflorescence in CDWG. These findings also bring insights into efflorescence mitigation schemes and mechanisms of geopolymer sourced from other materials. Highlights: The efflorescence mitigation in CDW geopolymer is for the first time investigated. Both MK and GGBS can mitigate the efflorescence but through different mechanisms. MK decreases the free alkalis while GGBS impedes the migration of alkalis. GGBS cannot reduce the risk of internal efflorescence. Al-rich admixture (e.g., MK) is a better choice for the efflorescence mitigation.