Understanding the new-to-old interfacial bonding mechanism of geopolymer for concrete repair: insight into effects of surface moisture of substrate
Understanding the new-to-old interfacial bonding mechanism of geopolymer for concrete repair: insight into effects of surface moisture of substrate
Geopolymer, a waste-based material with excellent thermal, mechanical, or chemical properties and low embodied carbon, can serve as an effective repair material for structural rehabilitation. In this work, three kinds of cementitious substrates with varying surface moisture conditions were prepared before applying fresh geopolymer repair material, i.e., dry (C-D), ambient (C-A) and saturated (C-S). Interfacial flexural-tensile strength, direct tensile strength and slant shear strength were tested to evaluate the interfacial bonding strength of the geopolymer-cement composites, and the bonding mechanism was revealed through X-ray Diffraction (XRD) and Back Scattered Electron (BSE)-Energy Dispersive Spectrometer (EDS) methods. Interfacial bonding strength results indicate that having a dry substrate surface is disadvantageous for relatively long-term bonding performance. The interfacial product was found to be geopolymer gel from XRD and EDS analysis, with the Ca content of the interfacial products increasing with a rise in surface moisture. The “Overlay transition zone (OTZ)” was defined based on the wall effect of unreacted particles packing of repairing material, and its thickness was found to be ca. 30 µm. The OTZ thickness of samples with an initially dry concrete surface was greater than that with ambient moisture and water-saturated samples, and there were more unreacted particles within its OTZ. Finally, the complex effects of varying surface moisture were explained by the integrated analysis of interfacial products and microstructures.
Bonding mechanism, Geopolymer, New-to-old interface, Overlay Transition Zone (OTZ), Surface moisture
Xiong, Guiyan
df7f264c-c3ca-4efb-9069-f931712b5ff8
Guo, Xiaolu
428d8ca9-e880-4b20-b4df-25e7b2c094f1
Cundy, Andrew
994fdc96-2dce-40f4-b74b-dc638286eb08
Hashem, Fayza S.
960d104f-1af3-4de0-aecd-2b3386158adf
Wu, Min
c3b38f95-9bb1-46a6-946b-5245707abb9a
20 August 2025
Xiong, Guiyan
df7f264c-c3ca-4efb-9069-f931712b5ff8
Guo, Xiaolu
428d8ca9-e880-4b20-b4df-25e7b2c094f1
Cundy, Andrew
994fdc96-2dce-40f4-b74b-dc638286eb08
Hashem, Fayza S.
960d104f-1af3-4de0-aecd-2b3386158adf
Wu, Min
c3b38f95-9bb1-46a6-946b-5245707abb9a
Xiong, Guiyan, Guo, Xiaolu, Cundy, Andrew, Hashem, Fayza S. and Wu, Min
(2025)
Understanding the new-to-old interfacial bonding mechanism of geopolymer for concrete repair: insight into effects of surface moisture of substrate.
Construction and Building Materials, 493, [143201].
(doi:10.1016/j.conbuildmat.2025.143201).
Abstract
Geopolymer, a waste-based material with excellent thermal, mechanical, or chemical properties and low embodied carbon, can serve as an effective repair material for structural rehabilitation. In this work, three kinds of cementitious substrates with varying surface moisture conditions were prepared before applying fresh geopolymer repair material, i.e., dry (C-D), ambient (C-A) and saturated (C-S). Interfacial flexural-tensile strength, direct tensile strength and slant shear strength were tested to evaluate the interfacial bonding strength of the geopolymer-cement composites, and the bonding mechanism was revealed through X-ray Diffraction (XRD) and Back Scattered Electron (BSE)-Energy Dispersive Spectrometer (EDS) methods. Interfacial bonding strength results indicate that having a dry substrate surface is disadvantageous for relatively long-term bonding performance. The interfacial product was found to be geopolymer gel from XRD and EDS analysis, with the Ca content of the interfacial products increasing with a rise in surface moisture. The “Overlay transition zone (OTZ)” was defined based on the wall effect of unreacted particles packing of repairing material, and its thickness was found to be ca. 30 µm. The OTZ thickness of samples with an initially dry concrete surface was greater than that with ambient moisture and water-saturated samples, and there were more unreacted particles within its OTZ. Finally, the complex effects of varying surface moisture were explained by the integrated analysis of interfacial products and microstructures.
Text
Manuscript-R2-revised-unmarked
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More information
Accepted/In Press date: 13 August 2025
e-pub ahead of print date: 20 August 2025
Published date: 20 August 2025
Keywords:
Bonding mechanism, Geopolymer, New-to-old interface, Overlay Transition Zone (OTZ), Surface moisture
Identifiers
Local EPrints ID: 506042
URI: http://eprints.soton.ac.uk/id/eprint/506042
ISSN: 0950-0618
PURE UUID: 63f97189-5846-4747-bcc3-97a748d9118c
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Date deposited: 28 Oct 2025 17:34
Last modified: 29 Oct 2025 02:49
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Contributors
Author:
Guiyan Xiong
Author:
Xiaolu Guo
Author:
Fayza S. Hashem
Author:
Min Wu
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