Enhancing the performance of NaOH-activated slag using waste green tea extract as a multi-function admixture

This study attempts to utilize waste green tea extract (WT) primarily containing tea polyphenol (TP) as a multi-function admixture to improve the performance of alkali-activated slag (AAS) while achieving resource utilization of tea waste. WT was added as a substitute for mixing water. The experimental results showed that the introduction of WT resulted in a significant increase in the setting time and an improvement in the flowability of AAS. Hydration kinetics analysis revealed that the use of WT exhibits both a retarding effect and an accelerating effect on the hydration of slag. When a lower concentration of WT was added, the accelerating effect could dominate the hydration process of AAS, conversely, the retarding effect takes dominates. Moreover, WT also contributes to improving the pore structure of AAS, resulting in a denser microstructure and thus enhancing the compressive strength and micro-mechanical properties of AAS. More importantly, the addition of WT effectively reduces the autogenous shrinkage of AAS. By adding WT with proper concentrations, the compressive strength of the AAS mortar can be maximumly increased by 44.8 % at 7d and 50.9 % at 28d, respectively, and decreased the autogenous shrinkage by as high as 59.8 % compared to the control mortar.