Binder Chemistry – High-Calcium Alkali-Activated Materials

Bernal, Susan A.; Provis, John L.; Fernández-Jiménez, Ana; Schroeyers, Wouter; Kаvalerova, Еlena; Palacios, Marta; Shi, Caijun

doi:10.1007/978-94-007-7672-2_3

Cited by 64 publications

(51 citation statements)

References 133 publications

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“…Such alkali activated slags can have high-strength development and using the adequate activators can lead to rapid setting and hardening, good durability and high resistance to chemical attack. [5,14,15,[18][19][20][21] The main hydration products are calcium silicate hydrates containing aluminum (C-A-S-H) with a low Ca/Si ratio (≈1), a hydrotalcite-like phase, and in some cases also an AFm phase, most likely strätlingite. [18,19,[22][23][24][25][26][27][28][29][30] Many variables influence the reaction of alkali-activated slags such as slag fineness and chemical composition, type, and concentration of the alkaline activator, water/binder (w/b) ratio, temperature, or pH.…”

Section: Introductionmentioning

confidence: 99%

Influence of slag composition on the hydration of alkali-activated slags

Winnefeld

Haha

Saoût

et al. 2014

Journal of Sustainable Cement-Based Materials

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The hydration of different blast-furnace slags with sodium metasilicate or NaOH as activator was investigated. Sodium metasilicate shows poor strength after 1 day, but high strength after 7 days and beyond, whereas NaOH activation leads to high strength after 1 day , but only moderate strength development at later ages. At the same hydration degree, sodium metasilicate activation gives a much higher compressive strength than NaOH activation. This is due to the formation of a dense hydration product in the NaOH-activated system at the early age, which leads to a more porous microstructure than in the case of sodium metasilicate. A higher MgO content in the slags is beneficial with respect to faster hydration kinetics and a more rapid strength development. Increasing Al 2 O 3 contents lead to slightly slower hydration kinetics and slightly lower compressive strengths. The best correlation between compressive strength and slag composition was found using the extended basicity (CaO + MgO)/SiO 2 index.

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Section: Introductionmentioning

confidence: 99%

Influence of slag composition on the hydration of alkali-activated slags

Winnefeld

Haha

Saoût

et al. 2014

Journal of Sustainable Cement-Based Materials

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“…The use of these near neutral salts has the added value of minimising potential hazards associated with handling of highly alkaline solutions, and reducing the embodied energy and environmental impact allocated to the activating solution used for producing alkali-activated cements. However, the alkali-activation of slags using these salts has received relatively little attention, as the binders produced usually take a longer time to harden than is commercially required by the construction industry, and can show delayed compressive strength development except when heat curing is applied [25].…”

Section: Brief Overview Of Alkali-activated Slag Materialsmentioning

confidence: 99%

“…The sulfate activation of slags typically leads to the formation of a C-A-S-H type phase with a low Ca/Si ratio, and ettringite as the main secondary reaction product [25,[38][39][40]. The setting of Na 2 SO 4 -activated slag cements is much faster than is identified in Na 2 CO 3 -activated slags [36], although these materials take a longer time to harden than sodium-silicate activated slag cements.…”

Section: Sodium Sulfate Activated Slag Cementsmentioning

confidence: 99%

Advances in near-neutral salts activation of blast furnace slags

Bernal

2016

RILEM Tech Lett

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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...

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“…When BFS reacts with a source of alkalis to form a hardened binder, the main reaction 76 product and strength-giving phase is a calcium-silicate-hydrate (C-S-H) type phase with a 77 low Ca/Si ratio and a significant degree of aluminium substitution, termed C-A-S-H [10,11].…”

mentioning

confidence: 99%