Preliminary Interpretation of the Induction Period in Hydration of Sodium Hydroxide/Silicate Activated Slag

Zuo, Yibing; Ye, Guang

doi:10.3390/ma13214796

Cited by 33 publications

(19 citation statements)

References 57 publications

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“…The effect of the activators at the same concentration of 4 mol Na + /dm 3 is shown in Figure 1 . The general calorimetric response for each alkali activator was in agreement with those reported by Shi and Day more than 25 years ago [ 45 ], and more recently by other authors [ 33 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 ]. All pastes showed an initial peak just after placing the sample in the calorimeter, which originates from the wetting and initial dissolution of the slag grains and the energy absorbed by the sample during the mixing.…”

Section: Resultssupporting

confidence: 90%

“…Then, the calorimetric response was strongly affected by the activators’ nature. SHAS did not show an induction period [ 33 , 53 ] and the second peak started just after the initial peak, indicating large amounts of precipitated hydration products—especially the C-A-S-H gel. In the case of SCAS and SWGAS, a second peak adjacent to the initial peak also occurred.…”

Section: Resultsmentioning

confidence: 99%

“…Before this third main hydration peak occurred, a distinguishable induction period occurred. For SWGAS, the induction period was attributed to the slowing of slag dissolution, due to the high concentration of dissolved Si [ 33 ]. This very long induction period is a common issue of SCAS [ 41 , 53 , 56 ].…”

Section: Resultsmentioning

confidence: 99%

“…In addition to the above-mentioned aspects, the activator composition and concentration are another key parameter affecting the dissolution of the slag, as well as the composition of the hydration products, the rate of their formation, etc. One tool for the reasonable prediction of which solid products will be able precipitate (if any), i.e., to assess the under/supersaturation of the solution with respect to the given solid phase, is the so-called effective saturation index, described elsewhere [ 30 , 32 , 33 ]. The formation of reaction products can also be modeled using GEM-Selektor, which is a software that works based on the minimization of Gibbs energy [ 34 , 35 ].…”

Section: Introductionmentioning

confidence: 99%

“…The anionic groups of sodium carbonate and sodium silicate activators are present in high concentrations from the beginning of the mixing process. This affects the dissolution of the aluminosilicate precursor; for example, the leaching of Si from slag is hampered by a high concentration of silicates [ 33 ], but also results in the formation of various early hydration products prior to the main hydration stage. This in turn significantly affects the properties of AAS in the very early stages—typically its rheology and setting time, as well as the further hydration processes.…”

Section: Introductionmentioning

confidence: 99%

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Experimental Study of Slag Changes during the Very Early Stages of Its Alkaline Activation

et al. 2021

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The very early stages of alkaline activation of slag control its rheology and setting, but also affect its hydration, which occurs later. Simultaneously, these parameters are dictated by the nature and dose of the alkaline activator. Therefore, we investigated and compared the changes in slag particles (SEM, BET, laser diffraction), as well as in the pore solution composition (ICP–OES), pH, and conductivity, of alkali-activated slag (AAS) pastes containing the three most common sodium activators (waterglass, hydroxide, and carbonate) and water during the first 24 h of its activation. To ensure the best possible comparability of the pastes, a fairly nontraditional mixture design was adopted, based on the same concentration of Na+ (4 mol/dm3) and the same volume fraction of slag in the paste (0.50). The results were correlated with the pastes’ hydration kinetics (isothermal calorimetry), structural build-up (oscillatory rheology), and setting times (Vicat). Great differences were observed in most of these properties, in the formation of hydration products, and in the composition of the pore solution for each activator. The results emphasize the role of the anionic groups in the activators and of the pH, which help predict the sample’s behavior based on its calorimetric curve, and offer data for further comparisons and for the modelling of AAS hydration for specific activators.

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Section: Resultssupporting

confidence: 90%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Experimental Study of Slag Changes during the Very Early Stages of Its Alkaline Activation

et al. 2021

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Extension of the fib MC 2010 for basic and drying shrinkage of alkali‐activated slag concretes

Caron

Patel

Dehn

2022

Structural Concrete

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Alkali-activated slag is an alternative to ordinary Portland cement that has been studied for the past 20 years. One of the main challenges for its practical use is understanding and controlling its shrinkage behavior. In this study, new experimental results for two alkali-activated slag concrete mixes are presented under both sealed and unsealed conditions. The results show that basic shrinkage increases with increased sodium silicate ratio. Under unsealed conditions, the age to exposure to drying has a most significant impact on the final drying shrinkage. Finally, the mechanisms explaining shrinkage of such materials are discussed and thefib Model Code 2010 is extended for alkali-activated slag concrete using the new experimental results. The extended model consists of four parameters influencing the final values and the speed of both basic shrinkage and drying shrinkage. It is extensively compared with experimental datasets from the literature and improves significantly predictions compared with the original models for both basic and drying shrinkage. This demonstrates clearly the feasibility to extend it for predicting shrinkage of alkali-activated slag concrete.

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Evaluation of copper slag and stainless steel slag as replacements for blast furnace slag in binary and ternary alkali-activated cements

et al. 2023

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Commonly used alkali activation precursors such as blast furnace slag and fly ash will soon become less available due to resource competition, and may cease to be produced in certain regions. This limitation in future supply is a main driving force for the investigation of alternative precursor sources, such as non-blast furnace slags and non-ferrous slags, to produce alkali-activated binders. The current study investigates the incorporation of copper slag (CS) and stainless steel slag resulting from electric arc furnace operations (EAFSS) as partial replacements for ground granulated blast furnace slag (GGBFS) in producing alkali-activated materials (AAMs), at paste level. Five binary alkali-activated mixtures with different replacement levels of GGBFS with CS, and three ternary mixtures with both CS and EAFSS as partial and total replacements for GGBFS, are activated by a sodium silicate solution. Replacing GGBFS with CS and EAFSS retards the reaction kinetics, resulting in improved fresh-state properties of the investigated AAMs, better retention of workability and longer setting times. The reaction of alkali-activated 100% CS shows minimal initial exothermic activity until 3.5 h, when a single intense peak appears, representing delayed dissolution and subsequent polycondensation. X-ray diffraction (XRD) data indicate that the main crystalline phases of CS and EAFSS are stable in these alkaline systems; it is the glassy components that react. The use of CS and EAFSS in blended AAMs causes a minor increase in porosity of ~ 1–3% with respect to GGBFS only, and a small reduction in compressive and flexural strengths, although these reach 80 MPa and 8 MPa, respectively, after 28 days, even at a replacement level over 65 wt. %. Conversely, the 100% CS mixture exhibits a one-day compressive strength of 23 MPa, with a negligible increase thereafter. This result agrees with both FTIR and SEM analysis which highlight only minor changes in binder development after two days. It is believed that the unusual behaviour of CS in the investigated mixtures is related to the low availability of calcium in this precursor material.

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Preliminary Interpretation of the Induction Period in Hydration of Sodium Hydroxide/Silicate Activated Slag

Cited by 33 publications

References 57 publications

Experimental Study of Slag Changes during the Very Early Stages of Its Alkaline Activation

Experimental Study of Slag Changes during the Very Early Stages of Its Alkaline Activation

Extension of the fib MC 2010 for basic and drying shrinkage of alkali‐activated slag concretes

Evaluation of copper slag and stainless steel slag as replacements for blast furnace slag in binary and ternary alkali-activated cements

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