Interaction of Polycarboxylate-Based Water-Reducing Admixture Molecular Structure with Fly Ash Substituted Cementitious Systems: Marsh-Funnel and Mini-Slump Performance

Abstract

Polycarboxylate ether-based high-range water-reducing admixtures (PCE) play a crucial role in enhancing the workability of fly ash-substituted cementitious systems. Alterations to the chemical structures of both the main and side chains can particularly enhance the electrostatic repulsion and steric hindrance effects of PCEs. As a consequence, this results in improved performance within cementitious systems containing fly ash substitutions. This study investigated the compatibility of the altered molecular structure of polycarboxylate ether (PCE) with cementitious systems containing fly ash substitutions. To achieve this, five polymers were synthesized, varying the side chain length, molecular weight, main chain length, and main chain lengths of PCEs while maintaining other properties constant. Cement pastes were then prepared using the synthesized PCEs with fly ash replacements at three different rates. Marsh-funnel flow time and mini-slump values were measured in the prepared mixtures. The study revealed that in mixtures without fly ash, PCEs with a long main chain (40k) and short side chain length (1000 g/mole) exhibited the lowest Marsh-funnel flow and mini-slump performance among PCEs with diverse molecular structures. For the other PCEs in these mixtures, the change in molecular structure did not significantly affect their performance. However, as the fly ash replacement rate increased, PCE having a medium main chain (21k) and side chain (2400 g/mole) length outperformed other PCEs in terms of Marsh-funnel flow and mini-slump performance.