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Workability improvement of alkali-activated materials by common plasticizers used for ordinary Portland cement is usually an issue, but certain effectiveness is often found for lignosulfonate-based plasticizers (LS), especially for activation with sodium hydroxide (its silicate modulus considered as zero). Therefore, the action of LS depending on the silicate modulus of the activator (0, 0.10, 0.25, 0.50) was studied in this paper, using non-traditional oscillation strain sweep tests. The results showed that LS works for silicate moduli of 0 and 0.10 especially in terms of great reduction in the viscoelastic moduli due to a significant decrease in zeta potential magnitude. However, LS had a marginal effect for the silicate moduli of 0.25 and 0.50, which was attributed to the competitive adsorption of LS and silicates from waterglass onto the slag grains. Although splitting of LS chains in NaOH was proven using X-ray photoelectron spectroscopy, electrostatic repulsion of smaller fragments is preserved. [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]

Hybrid systems represent a new sustainable type of cement combining the properties of ordinary Portland cement and alkali-activated materials. In this study, a hybrid system based on blast furnace slag and Portland clinker was investigated. The economic aspects and appropriate waste management resulted in the usage of technological waste from water glass production (WG-waste) as an alkaline activator. Although the Portland clinker content was very low, the incorporation of this by-product significantly improved the mechanical properties. Nevertheless, the high amount of alkalis in combination with possible reactive aggregates raises concerns about the risk of alkali–silica reaction (ASR). The results obtained from expansion measurement, the uranyl acetate fluorescence method, and microstructure characterization revealed that the undesirable effects of alkali–silica reaction in mortars based on the hydration of hybrid cement are minimal. [ABSTRACT FROM AUTHOR]