Effects of activator characteristics on the reaction product formation in slag binders activated using alkali silicate powder and NaOH

Ravikumar, Deepak; Neithalath, Narayanan

doi:10.1016/j.cemconcomp.2012.03.006

Cited by 185 publications

(84 citation statements)

References 38 publications

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“…This phenomenon can be explained by the higher level of nucleation sites created by smaller aggregates (Ben Haha et al, 2011), or by a reduction of the characteristic thickness of the paste as in OPC , and thus a thinner ITZ, due to the larger aggregate surface area. This theory is supported by the ESEM results presented below, in agreement with previous analysis of metakaolin-based alkali-activated mortars (Ravikumar and Neithalath, 2012). seM, Bse, and eDX study A comparison of the microstructural characteristics of the ITZ regions in AAS and PC mortars, as identified by ESEM (BSE) analysis and grayscale segmentation as outlined in Section "Quantification of Data from BSE Images, " is presented in Figure 4.…”

Section: Quantification Of Data From Bse Imagessupporting

confidence: 77%

The Interfacial Transition Zone in Alkali-Activated Slag Mortars

Nicolas

Provis

2015

Front. Mater.

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The interfacial transition zone (ITZ) is known to strongly influence the mechanical and transport properties of mortars and concretes. This paper studies the ITZ between siliceous (quartz) aggregates and alkali-activated slag (AAS) binders in the context of mortar specimens. Backscattered electron (BSE) images generated in an environmental scanning electron microscope (ESEM) are used to identify unreacted binder components, reaction products, and porosity in the zone surrounding aggregate particles, by composition and density contrast. X-ray mapping is used to exclude the regions corresponding to the aggregates from the BSE image of the ITZ, thus, enabling analysis of only the binder phases, which are segmented into binary images by gray level discrimination. A distinct yet dense ITZ region is present in the AAS mortars, containing a reduced content of unreacted slag particles compared to the bulk binder. The elemental analysis of this region shows that it contains a (C,N)-A-S-H gel that seems to have a higher content of Na (potentially deposited through desiccation of the pore solution) and a lower content of Ca than the bulk inner and outer products forming in the main binding region. These differences are potentially important in terms of long-term concrete performance, as the absence of a highly porous ITZ region is expected to provide a positive influence on the mechanical and transport properties of AAS concretes.

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Section: Quantification Of Data From Bse Imagessupporting

confidence: 77%

The Interfacial Transition Zone in Alkali-Activated Slag Mortars

Nicolas

Provis

2015

Front. Mater.

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“…The sharp peak at around 946 cm -1 is generally observed for sodium carbonate activated slags of the generated C-(A)-S-H [25,42], while for the waterglass activated slags the position of this peak shifts to a higher wavenumber between 950 and 1000 cm -1 [52][53][54], pointing to a different chemical proportion (Si/Ca ratio) [51,55,56]. Nevertheless, the LP incorporation does not affect the peak position, indicating that the gel structure of C-(A)-S-H remains the same regardless of the LP dosages.…”

Section: Ft-irmentioning

confidence: 99%

Assessing the chemical involvement of limestone powder in sodium carbonate activated slag

Yuan

Brouwers

2017

Mater Struct

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This study aims to investigate the effect of limestone powder (LP) on the reaction of sodium carbonate activated slag. The results show that the incorporated LP up to 30% improves the strength development, especially at advanced curing ages. A slightly accelerated reaction is observed for samples containing low amount of LP (B5%), while mixture with 10% LP shows the optimized results with respect to the heat release and strength development. Chemical effect of incorporating LP is observed at high replacement levels (C15%), indicated by the formation of a new phase, natron (Na 2 CO 3 Á10H 2 O). Besides, relatively high contents of hydrotalcite-like phases are generated when increasing the dosage of limestone powder. The chemical changes, including the volume changes of generating natron and the transformation of natron to calcite, is potentially responsible for the enhanced mechanical properties.

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“…While a higher alkalinity (as indicated by a lower M s ) is beneficial at early times to aid in dissolution of the glassy species in slag as shown by the heat release curves shown in Fig. 2a, a higher silica content is ultimately necessary to form the strength imparting C-(A)-S-H gel in the alkaliactivated systems (Hajimohammadi et al 2011;Ravikumar and Neithalath 2012b). The alkali cations could also be incorporated into the C-(A)-S-H gel.…”

Section: Early Age Reaction Response and Compressive Strengthmentioning

confidence: 99%

Microstructural, Mechanical, and Durability Related Similarities in Concretes Based on OPC and Alkali-Activated Slag Binders

Vance

Aguayo

Dakhane

et al. 2014

Int J Concr Struct Mater

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Alkali-activated slag concretes are being extensively researched because of its potential sustainability-related benefits. For such concretes to be implemented in large scale concrete applications such as infrastructural and building elements, it is essential to understand its early and long-term performance characteristics vis-à-vis conventional ordinary portland cement (OPC) based concretes. This paper presents a comprehensive study of the property and performance features including early-age isothermal calorimetric response, compressive strength development with time, microstructural features such as the pore volume and representative pore size, and accelerated chloride transport resistance of OPC and alkali-activated binder systems. Slag mixtures activated using sodium silicate solution (SiO 2 -to-Na 2 O ratio or M s of 1-2) to provide a total alkalinity of 0.05 (Na 2 O-tobinder ratio) are compared with OPC mixtures with and without partial cement replacement with Class F fly ash (20 % by mass) or silica fume (6 % by mass). Major similarities are noted between these binder systems for: (1) calorimetric response with respect to the presence of features even though the locations and peaks vary based on M s , (2) compressive strength and its development, (3) total porosity and pore size, and (4) rapid chloride permeability and non-steady state migration coefficients. Moreover, electrical impedance based circuit models are used to bring out the microstructural features (resistance of the connected pores, and capacitances of the solid phase and pore-solid interface) that are similar in conventional OPC and alkali-activated slag concretes. This study thus demonstrates that performance-equivalent alkali-activated slag systems that are more sustainable from energy and environmental standpoints can be proportioned.

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Effects of activator characteristics on the reaction product formation in slag binders activated using alkali silicate powder and NaOH

Cited by 185 publications

References 38 publications

The Interfacial Transition Zone in Alkali-Activated Slag Mortars

The Interfacial Transition Zone in Alkali-Activated Slag Mortars

Assessing the chemical involvement of limestone powder in sodium carbonate activated slag

Microstructural, Mechanical, and Durability Related Similarities in Concretes Based on OPC and Alkali-Activated Slag Binders

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