Effectiveness of common water-reducing admixtures in alkali-activated slag pastes with different types of activator

V Bilek,V Iliushchenko,L Kalina,P Hruby

doi:10.1088/1757-899x/1205/1/012001

V Bilek, V Iliushchenko + Show 2 more

Open Access

https://doi.org/10.1088/1757-899x/1205/1/012001

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Abstract

Rheology of alkali-activated slag (AAS) is a very complex issue, where the activator nature as well as its dose play an important role. Moreover, the use of water-reducing admixtures in these systems is an issue, as they often do not work properly. This could be attributed to the high pH as well as to the surface chemistry of AAS. Therefore, lignosulfonate-, polynaphthalene- and polycarboxylate-based superplasticizers were used to modify AAS pastes with sodium waterglass, hydroxide and carbonate activator. These pastes were tested using a rotational rheometer in an oscillatory shear mode of increasing shear strain to observe the evolution of viscoelastic moduli and to determine the oscillatory stress corresponding to the linear viscoelastic region limit (“yield point”) and to the crossover point, where the storage modulus equals the loss modulus (“flow point”). In most cases, the used plasticizers did not improve the rheological properties; the only exception was the lignosulfonate one in sodium hydroxide-activated slag.

Highlights

Rheological parameters are the key characteristics of any binder system and strongly affect its further performance
The fact that G′ > G′′ at low or intermediate strains indicates that activated slag (AAS) pastes have cross-linked structure originating from attractive forces acting between the pastes’ components
It is worth comparing the rheological properties of AAS pastes with respect to the activator type and without the added plasticizer

Summary

Introduction

Rheological parameters are the key characteristics of any binder system and strongly affect its further performance. The water content should be as low as possible to achieve higher mechanical properties, lower porosity and higher durability For this purpose, plenty of water-reducing admixtures or superplasticizers (SPs) have been developed and their increasingly sophisticated development continues in an unprecedented way. The above-mentioned stands for the Portland cement-based concretes, while the use of conventional SPs and other organic admixtures in alkali-activated materials often fails. This is most often attributed to their decreased stability due to very high pH [1,2,3], but the surface chemistry and presence of dissolved species are very important aspects [4, 5].

Experimental part

Results and discussion

Conclusions