Décalcification resistance of various alkali-activated materials

Hrubý, Petr; Bílek, Vlastimil; Topolář, Libor; Kalina, Lukáš; Marko, Michal; Šoukal, František; Dvořák, Richard; Hercik, T

doi:10.1088/1757-899x/1205/1/012015

Cited by 6 publications

(6 citation statements)

References 7 publications

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“…At later stages, a greatly different extent of increase in compressive strengths was recorded. The highest values of strength were reached by activation with SWG, which correlates with the results from the literature [7,10,15,17,20]. A very significant increase in the value of compressive strengths compared to the early stages was observed for SC, reaching from 50 to 70 MPa after 28 days, depending on the slag volume fraction.…”

Section: Mechanical Propertiessupporting

confidence: 88%

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Influence of activator type and slag volume fraction on properties of alkali-activated slag pastes

Hajzler

Bílek²,

Kotrla³

et al. 2022

J. Phys.: Conf. Ser.

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Alkali-activated systems belong to the group of alternative inorganic binders in which the binder properties are dictated by both the aluminosilicate precursor and alkaline activator. In this work, blast furnace slag and three different alkaline activators, namely sodium hydroxide, sodium water glass, and sodium carbonate, were selected. An innovative mixture design based on the same concentration of alkali (Na+) of 4 mol/dm3 for all activators and different volume fractions of slag in pastes, ranging from 0.44 to 0.54, was investigated by the flow table test, compressive and flexural strength test, and by a shrinkage test under autogenous conditions. Great differences for various activators for all investigated parameters were obtained. The highest fluidity, regardless of volume fraction of the slag, was observed for the water glass, originating from a greatly decreased yield stress compared to the two other activators. The type of activator and the volume fraction of the slag also played a crucial role in the development of shrinkage and strength.

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Section: Mechanical Propertiessupporting

confidence: 88%

“…Other advantageous aspects of AAS are resistance to aggressive environments [4][5][6][7], or resistance to high temperatures [4]. AAS is also popular due to its fast strength development even in laboratory conditions.…”

Section: Introductionmentioning

confidence: 99%

Influence of activator type and slag volume fraction on properties of alkali-activated slag pastes

Hajzler

Bílek²,

Kotrla³

et al. 2022

J. Phys.: Conf. Ser.

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“…In carbonate solutions, alkali permeation occurred only a few millimeters below the sample surface, which was due to a combination of several different factors such as surface carbonate degradation, partial CASH gel formation below the surface, or crystallization of the reagent in the pores and micropores of the TS. This carbonate degradation induced the formation of calcite from portlandite and a general decrease in alkalinity in the affected area, as also described in [54][55][56]. In the images of the TS microstructure in Figure 7, all these factors were observed.…”

Section: Monitoring the Depth Of Diffusion Of Alkali Ions Into The Ts...supporting

confidence: 55%

Monitoring of Ion Mobility in the Cement Matrix to Establish Sensitivity to the ASR Caused by External Sources

et al. 2022

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The possibility of the formation of an alkali–silicate reaction (ASR) is a crucial issue for the service life of concrete. The coexistence of key parameters such as the presence of alkalis, reactive SiO2, humidity, and temperature predetermine the possibility of its formation and application. When an ASR gel forms, it results in the concreting cracking and spalling as well as in the deterioration of its overall properties. The risk of ASR depends on the concentration of alkalis and their mobility, which influence their ability to penetrate the concrete. The objective of this study was to determine the ionic mobility of not only Na+ and K+, but Ca2+ as well, from external sources (0.5 and 1.0 mol/L solutions of Na/K carbonate, nitrate, and hydroxide) to a cementitious matrix as the precursor for ASR. The concentrations of ions in both the immersion solutions (ICP) and the cementitious matrix itself (SEM-EDX) were studied as a function of time, from 0 to 120 days, for leaching, and according to temperature (25 and 40 °C). The reaction products were characterized using SEM-EDX. Different diffusion rates and behavior were observed depending on the anion type of the external alkali source. Both sodium and potassium ions in all the three environments studied, namely carbonate, hydroxide, and nitrate, penetrated into the composite and further into its structure by different mechanisms. The action of hydroxides, in particular, transformed the original hydration products into calcium-silicate-hydrate (CASH) or ASR gel, while nitrates crystallized in pores and did not cause any changes in the hydration product. The driving force was the increased temperature of the experiment as well as the increased concentration of the solution to which the test specimen was exposed.

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“…The progress of the degradation reactions accompanied by the decrease of pH of matrices was evaluated using the phenolphthalein technique as defined in study [10]. The phenolphthalein is an acid-base indicator, which changes color with dependence on the pH.…”

Section: Phenolphthalein Techniquementioning

confidence: 99%

Resistance of alkali-activated blast furnace slag to acids

Hrubý

Bílek

Topolář

et al. 2022

J. Phys.: Conf. Ser.

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In this paper, the resistance of alkali-activated blast furnace slag to degradation processes caused by the action of various acids was studied. The ground granulated blast furnace slag was alkali-activated using sodium hydroxide in 6% Na2O dosage by the slag weight and subjected to testing of acid resistance in both organic and inorganic acidic solutions (pH ≈ 3) for 84 days. Citric, acetic, hydrochloric, and sulphuric acids were used for these purposes. The reference samples were stored in water. The progress of degradation was studied using the phenolphthalein technique, compressive strength testing, and weight measurements. Moreover, the SEM-EDX was used for the characterization of the degradation processes and microstructure changes. The degradation of alkali-activated blast furnace slag occurred in both organic and inorganic acids; however, the action of organic acids appears to be much more deteriorating. The decrease in compressive strength of about 50% and 60% was observed for acetic and citric acid, while only of 32% and 23% in sulphuric and hydrochloric, respectively.

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Décalcification resistance of various alkali-activated materials

Cited by 6 publications

References 7 publications

Influence of activator type and slag volume fraction on properties of alkali-activated slag pastes

Influence of activator type and slag volume fraction on properties of alkali-activated slag pastes

Monitoring of Ion Mobility in the Cement Matrix to Establish Sensitivity to the ASR Caused by External Sources

Resistance of alkali-activated blast furnace slag to acids

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