Thermodynamic modelling can reliably predict hydrated cement phase assemblages and chemical compositions, including their interactions with prevailing service environments, provided an accurate and complete thermodynamic database is used. Here, we summarise the Cemdata18 database, which has been developed specifically for hydrated Portland, calcium aluminate, calcium sulfoaluminate and blended cements, as well as for alkali-activated materials. It is available in GEMS and PHREEQC computer program formats, and includes thermodynamic properties determined from various experimental data published in recent years. Cemdata18 contains thermodynamic data for common cement hydrates such as C-S-H, AFm and AFt phases, hydrogarnet, hydrotalcite, zeolites, and M-S-H that are val-Cemdata18 includes a comprehensive selection of cement hydrates commonly encountered in Portland cement (PC) systems in the temperature range of to 100°C, including calcium silicate hydrate (C-S-H), magnesium silicate hydrate (M-S-H), hydrogarnet, hydrotalcite-like phases, some zeolites, AFm and AFt phases, and various solid solutions used to describe the solubility of these phases. Solubility constants have generally been calculated based on critical reviews of all available experimental data and from additional experiments made either to obtain missing data or to verify existing data. Additional solubility data were measured and compiled using temperatures ranging from 0 to 100°C in many instances, as documented in [9, 12, 27, 28]. Numerous solid solutions among AFm and AFt phases, siliceous hydrogarnets, hydrotalcite-like phases, C-S-H, and M-S-H have been observed and are included in Cemdata18. Several C-S-H solid solution models, as well as two models for hydroxide-hydrotalcite are available in Cemdata18. The CSHQ model from [11] and the OH-hydrotalcite end member with Mg/Al = 2 are well adapted for PC. Although the CSHQ model is able to describe the entire range of Ca/Si ratios encountered, it is best used for high Ca/Si C-S-H, as it still lacks the ability to predict aluminium uptake, which is of less importance for Portland cements than for blended cements. For alkali activated binders, the calcium (alkali) aluminosilicate hydrate (C-(N-)A-S-H) gel model, with lower calcium but higher aluminium and alkali content than in the C-S-H type phase which exists in hydrated PC, and a Mg-Al layered double hydroxide with variable Mg/Al ratio, are available. This paper summarises Cemdata18, which includes the most important additions to the Cemdata07 and Cemdata14 databases in recent years. It also discusses the relevance and implications of these additions, and compares Cemdata07 and Cemdata18, accounting for their main differences. Summaries

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.

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The structural development of a calcium (sodium) aluminosilicate hydrate (C-(N-)A-S-H) gel system, obtained through the reaction of sodium metasilicate and ground granulated blast furnace slag, is assessed by high-resolution 29 Si and 27 Al MAS NMR spectroscopy during the first 2 yr after mixing. The cements formed primarily consist of C-(N-)A-S-H gels, with hydrotalcite and disordered alkali aluminosilicate gels also identified in the solid product assemblages. Deconvolution of the 27 Al MAS NMR spectra enables the identification of three distinct tetrahedral Al sites, consistent with the 29 Si MAS NMR data, where Q 3 (1Al), Q 4 (3Al), and Q 4 (4Al) silicate sites are identified. These results suggest significant levels of crosslinking in the C-(N-)A-S-H gel and the presence of an additional highly polymerized aluminosilicate product. The mean chain length, extent of cross-linking, and Al/Si ratio of the C-(N-)A-S-H gel decrease slightly over time. The de-crosslinking effect is explained by the key role of Al in mixed cross-linked/non-cross-linked C-(N-)A-S-H gels, because the cross-linked components have much lower Al-binding capacities than the noncross-linked components. These results show that the aluminosilicate chain lengths and chemical compositions of the fundamental structural components in C-(N-)A-S-H gels vary in a way that is not immediately evident from the overall bulk chemistry.

Please cite this article as: Myers, R.J., Lothenbach, B., Bernal, S.A., Provis, J.L., Thermodynamic modelling of alkali-activated slag cements, Applied Geochemistry (2015), doi: http://dx. AbstractThis paper presents a thermodynamic modelling analysis of alkali-activated slag-based cements, which are high performance and potentially low-CO 2 binders relative to Portland cement. The has been applied to AAS cements in the past (Lothenbach and Gruskovnjak, 2007), however the calcium silicate hydrate (C-S-H) thermodynamic model (Kulik and Kersten, 2001) used in that study does not explicitly define the uptake of Al and Na which is needed to fully describe C-(N-)A-S-H gel. Chemically complete definitions of Al chemistry in the thermodynamic models used to simulate the phases formed in AAS-based cements are important in enabling accurate prediction of the chemistry of these cements. The inclusion of alkalis as a key component in thermodynamic models for C-(N-)A-S-H gel is also important to enable correct description of the solubility relationships of this phase under the high pH conditions (>12) and alkali concentrations (tens to hundreds of mmol/L) relevant to the majority of cementitious materials (Myers et al., 2014). The CNASH_ss thermodynamic model used in the current paper was recently developed (Myers et al., 2014) to formally account for Na and tetrahedral Al incorporated in Ca/Si < 1.3 C-(N-)A-S-H gel. Here, this thermodynamic model is used to simulate the chemistry of AAS cements activated by aqueous solutions of NaOH ((NH) 0.5 ), Na 2 SiO 3 (NS), Na 2 Si 2 O 5 (NS 2 ) and Nc. This thermodynamic model can describe a large set of solubility data for the CaO-(Na 2 O,Al 2 O 3 )-SiO 2 -H 2 O and AAS cement systems, and closely matches the published chemical compositions of calcium aluminosilicate hydrate (C-A-S-H) gel, and the volumetric properties of C-(N-)A-S-H gel measured in a sodium silicate-activated slag cement (Myers et al., 2014). The CNASH_ss thermodynamic model is assessed here in terms of the prediction of solid phase assemblages and the Al content of C-(N-)A-S-H gel over the bulk slag chemical composition range which is most relevant to AAS cement-based materials. These simulations are performed using the Gibbs energy minimisation software GEM-Selektor v.3 an updated definition of Mg-Al LDH intercalated with OH -(MA-OH-LDH), and including some zeolites and alkali carbonates. The results are discussed in terms of implications for the design of high performance AAS-based cements.

ReuseUnless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. KeywordsTemperature, Calcium-Silicate-Hydrate (C-S-H), Thermodynamic Calculations, Hydration Products, Blended Cement. AbstractThere exists limited information regarding the effect of temperature on the structure and solubility of calcium aluminosilicate hydrate (C-A-S-H). Here, calcium (alumino)silicate hydrate (C-(A-)S-H) is synthesised at Ca/Si = 1, Al/Si ≤ 0.15 and equilibrated at 7-80°C. These systems increase in phase-purity, long-range order, and degree of polymerisation of C-(A-)S-H chains at higher temperatures; the most highly polymerised, crystalline and crosslinked C-(A-)S-H product is formed at Al/Si = 0.1 and 80°C. Solubility products for C-(A-)S-H were calculated via determination of the solid-phase compositions and measurements of the concentrations of dissolved species in contact with the solid products, and show that the solubilities of C-(A-)S-H change slightly, within the experimental uncertainty, as a function of Al/Si ratio and temperature between 7°C and 80°C. These results are important in the development of thermodynamic models for C-(A-)S-H to enable accurate thermodynamic modelling of cement-based materials. IntroductionTemperatures experienced by cement and concrete based construction materials in service can vary greatly, due to heat evolution from cement hydration, variable ambient environmental conditions, steam curing, and other factors. understanding of the nature of C-S-H and other constituent phases in these systems at equilibrium [6][7][8][9] has meant that hydrated neat PC materials can be accurately described by thermodynamic modelling at temperatures from 5°C to above 80°C [10]. Extending this analysis to the CaO-Al 2 O 3 -SiO 2 -H 2 O system represents a major step toward applying this technique to hydrated PC blends with high replacement levels of supplementary cementitious materials, which are not fully described by existing thermodynamic models [11]. This will enable a much deeper understanding of the chemistry and phase composition, and hence durability, of these materials in service.The chemistry and structure of calcium (alumino)silicate hydrate (C-(A-)S-H) products at ambient conditions have been the subject of sustained research for more than half a...