A new insight into the working mechanism of PCE emphasizing the interaction between PCE and Ca2+ in fresh cement paste. (15th March 2021) - Tian, Hongwei
Graphical abstract: Highlights: PAA exhibits high adsorption amount, but inferior fluidizing effect in cement paste. The intermolecular crosslinking by Ca 2+ leads to the detrimental effect on fluidity. PCEs with long side chain and high side chain density effectively resist crosslinking. PCEs with long side chain present wider working window in terms of AA to TPEG ratio. Linear AA- co -AMPS copolymers show resistance to the multivalent cation crosslinking. Abstract: Linear polymer, polyacrylic acid (PAA), acrylic acid – 2-acrylamido-2-methylpropane sulfonic acid (AA- co -AMPS) copolymers, and comb-like PCE polymers were used to study their dispersing efficiency in fresh cement pastes with emphasing their interactions with Ca 2+ in solution. Fluidity tests show that PAA exhibits an effective fluidizing effect in MgO and CaCO3 systems, while it behaves inversely in cement paste despite its significant adsorption amount because of the deleterious bridging effect caused by Ca 2+ ions in the interstitial solution. Dynamic light scattering measurements reveal that the incorporation of side chains into the PAA backbone inhibits the ion-bridging effect, and the PCE with longer side chain and higher side chain density exhibits stronger tolerance to this effect. Interestingly, the AA- co -AMPS copolymers present strong resistance against the ion-crosslinking effect. This suggests that the highly hydrophilic repeating units may act similarly to the side chains in PCEs concerning providing steric hindrance.