Role of PCE Anionicity in Early Hydration and Setting Behavior of NaOH-Activated Slag Binder

Several studies have revealed that polycarboxylate superplasticizers (PCEs) with shorter side chains and higher anionicities can overcome challenges posed by the high alkaline environment and disperse alkali-activated slags (AASs). However, how adsorption-dispersion translates into macroscopic setting behavior and early hydration remains insufficiently understood. Here, a series of isoprenyl oxy poly-(ethylene glycol) ether (TPEG) PCEs were synthesized with an identical side-chain length (n _EO = 10) but different anionicities by varying the feeding molar ratio of acrylic acid (AA:TPEG = 3, 4.5, and 7), enabling the isolated investigation of anionicity effects. A comprehensive analysis was conducted on NaOH-activated slag using adsorption measurements, ζ-potential analysis, isothermal calorimetry, setting time determination, compressive strength testing, and XRD characterization. It was found that an increase in PCE anionicity could enhance adsorption by stronger Ca²⁺ complexation, providing not only better dispersion but also a longer setting time and slightly delayed and reduced heat flow peak. However, these drawbacks did not compromise early strength development because the high-anionicity PCE can promote better particle stabilization. It was proposed that the more effectively dispersed the system is, the more prolonged the dissolution process may become, leading to delayed local precipitation. Consequently, hydration progression may be sustained, resulting in a higher compressive strength. These findings provide insight into the role of polymer charge density in influencing hydration and strength evolution in the NaOH-activated slag.