A new insight into the working mechanism of PCE emphasizing the interaction between PCE and Ca~(2+) in fresh cement paste

摘要

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 Ca2+ 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 Ca2+ 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. (C) 2020 Elsevier Ltd. All rights reserved.