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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]

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]

Significant drying shrinkage is one of the main limitations for the wider utilization of alkali-activated slag (AAS). Few previous works revealed that it is possible to reduce AAS drying shrinkage by the use of shrinkage-reducing admixtures (SRAs). However, these studies were mainly focused on SRA based on polypropylene glycol, while as it is shown in this paper, the behavior of SRA based on 2-methyl-2,4-pentanediol can be significantly different. While 0.25% and 0.50% had only a minor effect on the AAS properties, 1.0% of this SRA reduced the drying shrinkage of waterglass-activated slag mortar by more than 80%, but it greatly reduced early strengths simultaneously. This feature was further studied by isothermal calorimetry, mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). Calorimetric experiments showed that 1% of SRA modified the second peak of the pre-induction period and delayed the maximum of the main hydration peak by several days, which corresponds well with observed strength development as well as with the MIP and SEM results. These observations proved the certain incompatibility of SRA with the studied AAS system, because the drying shrinkage reduction was induced by the strong retardation of hydration, resulting in a coarsening of the pore structure rather than the proper function of the SRA. [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]