20Binders formed through alkali-activation of slags and fly ashes, including 'fly ash 21 geopolymers', provide appealing properties as binders for low-emissions concrete production. 22However, the changes in pH and pore solution chemistry induced during accelerated 23 carbonation testing provide unrealistically low predictions of in-service carbonation resistance. 24The aluminosilicate gel remaining in an alkali-activated slag system after accelerated

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Structural models for the primary strength and durability-giving reaction product in modern cements, a calcium (alumino)silicate hydrate gel, have previously been based solely on noncrosslinked tobermorite structures. However, recent experimental studies of laboratory-synthesized and alkali-activated slag (AAS) binders have indicated that the calcium-sodium aluminosilicate hydrate (C-(N)-A-S-H) gel formed in these systems can be significantly crosslinked. Here, we propose a model that describes the C-(N)-A-S-H gel as a mixture of crosslinked and non-crosslinked tobermorite-based structures (the Crosslinked Substituted Tobermorite Model, CSTM), which can more appropriately describe the spectroscopic and density information available for this material.Analysis of the phase assemblage and Al coordination environments of AAS binders shows that it is not possible to fully account for the chemistry of AAS by use of the assumption that all of the tetrahedral Al is present in a tobermorite-type C-(N)-A-S-H gel, due to the structural constraints of the gel. Application of the CSTM can for the first time reconcile this information, indicating the 1 Preprint version of accepted article. Please cite as: R.J. Myers, S.A. Bernal, R. San Nicolas, J.L. Provis, "Generalized Structural Description of CalciumSodium Aluminosilicate Hydrate gels: The Crosslinked Substituted Tobermorite Model", Langmuir 2013, 29(17):5294-5306. Official journal version is online at http://dx.doi.org/ 10.1021 presence of an additional activation product that contains highly connected four-coordinated silicate and aluminate species. The CSTM therefore provides a more advanced description of the chemistry and structure of calcium-sodium aluminosilicate gel structures than that previously established in the literature.

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This is a repository copy of Role of carbonates in the chemical evolution of sodium carbonate-activated slag binders.