The Effect of Structural Stability of Chemical Admixtures on the NaOH Alkali-Activated Slag Properties

Abstract

The current study aims to construct a synthetic polymer (or family of polymers) with superior plasticizing properties in a highly alkaline medium. An invented laboratory-prepared superplasticizer (SP), namely phenol-formaldehyde sulfonilate (PFS), was synthesized, and its performance was measured against two types of commercial superplasticizers [naphthalene-based (Nb) and polycarboxylate-based (PCb)]. Fourier transform infrared (FTIR) and gel permeation chromatography (GPC) tests were performed to verify the admixture's stability in a highly alkaline medium. The interaction between different SPs and alkali-Activated slag (AAS) surface was investigated via zeta potential and adsorption measurements. The flowability, setting time, and compressive strength developments were evaluated for AAS mixes. The hydration products' morphologies and phase compositions were studied using scanning electron microscope (SEM) and X-ray diffraction (XRD). The results reveal that the prepared PFS SP has a high stability against the highly alkaline medium. The dispersing efficiency of PFS SP resulted from the highly negative zeta potential value (-49.8 mV) compared with Nb (-41.5 mV) and PCb (-15.8 mV), as well as its high adsorption percentage as PFS, Nb, and PCb adsorbed by 18.5%, 9.2%, and 3.7%, respectively. The PFS SP enhanced the physicomechanical properties for AAS because it combined several advantages at the same time compared to commercial superplasticizers; for instance, AAS pastes admixed with PFS SP have superior workability, acceptable setting time, and high early strength.