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This study investigates the relationships between the hydration kinetics of waterglass-activated slag and the development of its physical-mechanical properties, as well as its color change. To modify the calorimetric response of alkali-activated slag, hexylene glycol was selected from various alcohols for in-depth experiments. In presence of hexylene glycol, the formation of initial reaction products was restricted to the slag surface, which drastically slowed down the further consumption of dissolved species and slag dissolution and consequently delayed the bulk hydration of the waterglass-activated slag by several days. This allowed to show that the corresponding calorimetric peak is directly related to the rapid evolution of the microstructure and physical-mechanical parameters and to the onset of a blue/green color change recorded as a time-lapse video. Workability loss was correlated with the first half of the second calorimetric peak, while the most rapid increase in strengths and autogenous shrinkage was related to the third calorimetric peak. Ultrasonic pulse velocity increased considerably during both the second and third calorimetric peak. Despite the modified morphology of the initial reaction products, the prolonged induction period, and the slightly reduced degree of hydration induced by hexylene glycol, the overall mechanism of alkaline activation remained unchanged in the long-term perspective. It was hypothesized that the main issue of the use of organic admixtures in alkali-activated systems is the destabilizing effect of these admixtures on soluble silicates introduced into the system with an activator. [ABSTRACT FROM AUTHOR]

• Lignosulfonate efficient for NaOH activation regardless of the time of addition of paste components. • Calorimetry of alkali-activated slag with low silicate modulus of activator (0; 0.10; 0.25, 0.50). • Effect of lignosulfonate on rheology greatly related to its retarding effect on hydration. • The use and evaluation of strain amplitude sweep tests after different time discussed. • Hump on loss modulus curve for the pastes with significant precipitation of products. One of the crucial issues of alkali-activated materials is the application of conventional plasticizers. Lignosulfonate plasticizer (LS) works well for sodium hydroxide-activated slag but loses its efficiency in sodium waterglass-activated slag because of competitive adsorption with silicates. Therefore, the effects of the timing of LS and activator addition on the structural build-up and breakdown of AAS pastes with low-silicate moduli activator (0 to 0.50) were investigated, particularly by means of non-traditional strain sweep tests, which are thoroughly discussed. The rheological tests were correlated with the Vicat needle test and isothermal calorimetry. The results showed the high efficiency of LS in NaOH-activated slag paste over time, regardless of the order of addition of the components of the paste. It was accompanied by a considerable retardation effect of LS on the hydration of AAS. The beneficial effect of LS on the rheological parameters and hydration kinetics decreased rapidly with an increase of the silicate modulus of the activator. The delayed addition of the concentrated silicate-containing activators completely counteracted the slightly beneficial effect of LS and even accelerated the initial structural build-up. [ABSTRACT FROM AUTHOR]

The aim of this study was to explore the influence of ethylene glycol in a wide range of polymerization degree, i.e. from monomer (EG) up to polyethylene glycol (PEG) with molecular weight of about 35,000, on properties of alkali-activated slag mortars. Changes in molecular weight and dose of all tested glycols had only minor effect on compressive strength, while drying shrinkage was significantly affected by both these factors. EG had negligible impact on drying shrinkage, but other tested glycols reduced it significantly with PEG2000 and PEG10000 being the most effective. Such different shrinkage behavior was attributed to the changes in surface tension and pore structure. All tested glycols reduced the total heat released during the hydration and interestingly modified the heat flow depending on their molecular weight. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• Amino alcohol surfactants reduced the surface tension of AAS pore solutions. • Surfactants had a minor effect on autogenous shrinkage. • Drying shrinkage was reduced mainly thanks to hydration retardation caused by surfactants. • Decrease in surface tension does not necessarily lead to decrease in shrinkage. • Adsorption of surfactants on slag particles were observed. One of the most important technological problems associated with alkali-activated materials is high shrinkage. In this study, shrinkage reducing admixtures (SRAs) based on amino alcohols were used in alkali-activated slag (AAS) as strong surfactants that should, in terms of capillary pressure theory, decrease shrinkage via the decrease in surface tension. Although the surface tension of the pore solution was reduced by SRAs, autogenous shrinkage was not affected in the long run, while drying shrinkage was noticeably reduced and simultaneous weight changes were dramatically increased. The expected retardation effect of SRAs on hydration was confirmed using isothermal calorimetry, strength development, mercury intrusion porosimetry and scanning electron microscopy. The obtained results suggest that the observed effect of SRAs on drying shrinkage was caused by coarser pore structure rather than by a decrease in surface tension of the pore solution. Since the decrease in surface tension does not necessarily lead to decrease in shrinkage, the application of capillary pressure theory in AAS can sometimes be an issue. [ABSTRACT FROM AUTHOR]