The fate of iron in blast furnace slag particles during alkali-activation

et al. 2015

Applied Geochemistry

Self Cite

184

132

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.

Section: Occurrence Of Mg Fe and S-bearing Phasesmentioning

confidence: 81%

Thermodynamic modelling of alkali-activated slag cements

Myers

Lothenbach

et al. 2015

Applied Geochemistry

Self Cite

184

132

“…The influence of formulation parameters such as chemistry of the slag [9,10], type of activator [11], addition of metakaolin [12] or fly ashes [13], on the microstructural development and therefore performance of these materials have been the main focus of study in recent years. The application of advanced analytical techniques, including synchrotron X-ray diffraction [14] and X-ray fluorescence microscopy [15], along with thermodynamic modelling [16], have revealed detailed information about the chemistry and phase assemblage of these cements, allowing the development of descriptive models for the activation processes of slags ( Fig. 1).…”

Section: Brief Overview Of Alkali-activated Slag Materialsmentioning

confidence: 99%

Advances in near-neutral salts activation of blast furnace slags

2016

RILEM Tech Lett

“…The influence of formulation parameters such as chemistry of the slag [9, 10], type of activator [11], addition of metakaolin [12] or fly ashes [13], on the microstructural development and therefore performance of these materials have been the main focus of study in recent years. The application of advanced analytical techniques, including synchrotron X-ray diffraction [14] and X-ray fluorescence microscopy [15], along with thermodynamic modelling [16], have revealed detailed information about the chemistry and phase assemblage of these cements, allowing the development of descriptive models for the activation processes of slags (Fig. 1).…”

mentioning

confidence: 99%

Advances in near-neutral salts activation of blast furnace slags

2016

RILEM Tech Lett

The utilisation of near-neutral salts as activators to produce alkali-activated slag cements offers several technical advantages, including reduced alkalinity of the binders, minimising the risk associated with handling of highly alkaline materials, and better workability of the fresh paste compared to that of sodium silicate-activated slag cements. Despite these evident advantages, the delayed setting and slow early-age mechanical strength development of these cements have limited their adoption and commercialisation. Recent studies have demonstrated that these limitations can be overcome by selecting slags with chemistry, which is more prone to react with near-neutral salts, or by adding mineral additives. A brief overview of the most recent advances in alkali-activation of slags using either sodium carbonate or sodium sulfate as activators is reported, highlighting the role of material design parameters in the kinetics of reaction and phase evolution of these cements, as well as the perspectives for research and development of these materials.Keywords: Alkali-activation; Blast furnace slag; Sodium Carbonate; Sodium sulfate; Characterisation Brief overview of alkali-activated slag materialsAlkali-activated cements are materials produced via the chemical reaction of a poorly crystalline aluminosilicate powder, and a highly alkaline solution, to form a hardened solid. These materials have been studied for more than a century, and in the past decades one of the main drivers for their development has been the potential environmental benefits associated with their production [1]. Alkali activated cements are usually produced from industrial wastes or byproducts such as blast furnace slag derived from the ironmaking industry, fly ashes from the coal combustion process, among others [2], and are now commercialised in several places around the world [3]. These materials can develop desirable properties including high mechanical strength [4], good retention of integrity when exposed to high temperatures [5] and acidic media [6], if properly formulated and cured. Significant advances have been made over the past decade in understanding alkali-activated slag materials at micro-and macroscopic scales, as discussed in recent reviews [7,8], particularly for those materials produced with sodium silicate solutions as alkali-activator. The influence of formulation parameters such as chemistry of the slag [9, 10], type of activator [11], addition of metakaolin [12] or fly ashes [13], on the microstructural development and therefore performance of these materials have been the main focus of study in recent years. The application of advanced analytical techniques, including synchrotron X-ray diffraction [14] and X-ray fluorescence microscopy [15], along with thermodynamic modelling [16], have revealed detailed information about the chemistry and phase assemblage of these cements, allowing the development of descriptive models for the activation processes of slags (Fig. 1). Figure 1. Simplified schematic diagram of the alk...