Early-age deformation of hydrophobized metakaolin-based geopolymers

Ruan, Shengqian; Chen, Shikun; Liu, Yi; Zhang, Yajun; Yan, Dongming; Zhang, Mingzhong

doi:10.1016/j.cemconres.2023.107168

Cited by 12 publications

(2 citation statements)

References 76 publications

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“…Since autogenous shrinkage includes both Metakaolin underwent a dissolution-polymerization-polycondensation process with alkali activation [50]. First, metakaolin was rapidly dissolved in the alkaline aqueous solution, generating a large number of silicate and aluminate oligomers [42]. During this process, the density of the material decreased, and the chemical shrinkage of the MKG had a monotonically increasing period.…”

Section: Chemical Autogenous and Drying Shrinkagementioning

confidence: 99%

“…Yang et al found that the reaction of geopolymers based on fly ash and metakaolin drove the pore fluids to the autogenous shrinkage sites and reduced the capillary stresses, and autogenous shrinkage showed a negative trend (i.e., expansion) before it became positive (shrinkage) [41]. Ruan et al [42] found that the hydrophobic chemical groups introduced by polydimethylsiloxane (PDMS) and sodium methylsilicate (SMS) could be strongly bound to the geopolymer gel, giving the MKG a good water-repellent effect and thus reducing autogenous shrinkage by 91.1% and 41.8%, respectively. In terms of chemical shrinkage, PDMS improved the dispersion of the solid precursors, and SMS increased the alkalinity of the MKG, allowing the MKG to form a denser and more amorphous Si-rich gel, which reduced the chemical expansion of the MKG.…”

Section: Introductionmentioning

confidence: 99%

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Enhancing Volumetric Stability of Metakaolin-Based Geopolymer Composites with Organic Modifiers WER and SCA

Zhang,

Zang,

Shan

2024

Buildings

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Shrinkage during hardening and curing is one of the largest challenges for the widespread application of metakaolin-based geopolymers (MKGs). To solve this problem, a silane coupling agent (SCA) and waterborne epoxy resin (WER) were used to synthesize MKG composites. The individual and synergistic effects of the SCA and WER on chemical, autogenous, and drying shrinkage were assessed, the modification mechanisms were investigated by microstructural characterization, and shrinkage resistance was evaluated by the chloride ion permeability of MKG composite coatings. The results showed that the SCA and WER significantly decreased the chemical shrinkage, autogenous shrinkage, and drying shrinkage of the MKG, with the highest reductions of 46.4%, 131.2%, and 25.2% obtained by the combination of 20 wt% WER and 1 wt% SCA. The incorporation of the organic modifiers densified the microstructure. Compared with the MKG, the total volume of mesopores and macropores in MKG-WER, MKG-SCA, and MKG-WER-SCA decreased by 11.5%, 8.7%, and 3.8%, respectively. In particular, the silanol hydrolyzed from the SCA can react with the opened epoxy ring of the WER and the aluminosilicate oligomers simultaneously to form a compact network and resist shrinkage during the hardening and continuous reaction of the geopolymer. Furthermore, the apparently lowered chloride ion diffusion coefficient of concrete (i.e., reduction of 51.4% to 59.5%) by the WER- and SCA-modified MKG coatings verified their improved shrinkage resistance. The findings in this study provide promising methods to essentially solve the shrinkage problem of MKGs at the microscale and shed light on the modification mechanism by WERs and SCAs, and they also suggest the applicability of MKG composites in protective coatings for marine concrete.

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Section: Chemical Autogenous and Drying Shrinkagementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%