Dispersing Efficacy of Tailored IPEG PCEs in AAS Binders: Elucidating the Impact of PCE Molecular Weight

Abstract

In this study, the impact of the molecular weight of isoprenol ether-based (IPEG) polycarboxylate superplasticizers on the dispersing effectiveness in sodium hydroxide-activated slag binder and slag composite cement was investigated. For this purpose, a series of IPEG polycarboxylate ether (PCE) superplasticizers possessing the same anionicity and the same side chain length but varying molecular weights (13,000–400,000 Da) were prepared. The synthesized PCE polymers were then subjected to application-related tests. It was found that their dispersing capacity in the AAS binder differed significantly and that IPEG PCE polymers possessing higher molecular weight generally were more effective. Surprisingly, it was also noticed that in the slag composite cement (90% slag, 10% OPC), generally, higher doses of the PCEs were required than in the OPC-free AAS binder system. Moreover, the working mechanism behind the enhanced dispersing ability of high Mw IPEG PCEs was studied via adsorption and adsorbed layer thickness (ALT) measurements. To determine the ALT of the adsorbed PCE polymers, phosphate-modified polystyrene nanoparticles were selected as a model substrate. Results from dynamic light scattering revealed that high Mw PCEs produce thicker adsorbed layers, which highly benefits the dispersing power of the PCE polymers stemming from enhanced steric hindrance. Finally, different models for the adsorbed conformations of those IPEG PCEs are proposed based on their individual molecular characteristics.