Influence of mixing protocols on flow retention of one-part alkali activated slag systems

Poor workability and rapid flowability loss are among several challenges hindering the wider acceptance of alkali-activated slag (AAS) (i.e. shrinkage, efflorescence). Several attempts were made to solve this issue, focusing more on selected ingredients, proportions, type and dosage of admixtures, and addition sequence. This study shifted the focus to mixing protocol, highlighting its potential and effects on AAS flow retention considering mixing duration, sequence, and relaxation time. Various one-part AAS mixtures activated by 6 %, 8 %, and 10 % sodium metasilicate were tested. Mixing protocols were applied for 10-90 min, mixing with and without relaxation time. Mini-slump, flowability-loss rate, setting time, the heat of hydration, rheological properties, and compressive strength were evaluated. Changes in hydration products were also examined by XRD, FTIR and TGA. Pearson correlation coefficient and ANOVA were applied to identify the dominant factors. Results reveal the dependency of the optimum mixing protocol on the used activator dosage. A long mixing period with r intervals was more effective for high activator dosages due to the continuous breakdown of formed hydration products' links. Modifying the mixing protocol did not alter the amount of formed hydration products, regardless of the activator dosage. These findings pave the way to understanding the role played by the mixing protocol in mineral hydration for wider in-situ implementation of AAS and the flourishing potential of the ready-mix AAS market.