Ca²⁺‐Mediated Interaction Between Microsilica and Polycarboxylate Comb Polymers in a Model Cement Pore Solution

Abstract

Interaction between polycarboxylate (PCE) comb polymers and microsilica suspended in a highly alkaline, Ca2+‐loaded model cement pore solution was studied via zeta potential, adsorption, and paste flow experiments. Zeta potential measurements reveal that in an alkaline suspension, microsilica possesses a negative surface charge stemming from deprotonated silanolate groups. Addition of soluble calcium salts (e.g., CaCl2) was found to cause a charge reversal to positive, owing to the adsorption of Ca2+ ions forming a monolayer on the microsilica surface. Further experiments demonstrate that through Ca2+ mediation, anionic PCE graft polymers adsorb in high amount on the microsilica surface. Polymers possessing a stronger anionic character exhibit a higher affinity to the positive microsilica surface, and consequently, exercise a more powerful dispersing effect than PCE showing less anionic character. A model summarizing the processes occurring at the surface of microsilica in this fluid system is proposed. The study suggests that the high fluidity of concrete containing microsilica depends on the effective dispersion of microsilica, and not of cement.

Surface Chemistry of Calcium Aluminosilicate Glasses

“…B, even low concentrations of Ca lead to a significant increase in zeta potential in alkaline conditions. Ca shows strong ion–ion correlation with silicate surfaces in alkaline conditions and even low concentrations may thus lead to charge reversal . The release of Ca and Mg during the 15 min immersion may thus significantly increase the zeta potential.…”

Regulating the arm structure of star‐shaped polycarboxylate superplasticizers as a means to enhance cement paste workability

“…The absolute value of the negative potential on the surface of cement particles has been reported to increase with the adsorption of PCE . The electrostatic repulsion that results from the PCE enhanced the dispersion effect of the cement particles . Moreover, the introduced sulfonic acid groups enhanced the negative potential gross so that the dispersion effect obtained with SPCE3‐SM was greater than that observed with SPCE3.…”

First Seconds in a Building’s Life—In Situ Synchrotron X‐Ray Diffraction Study of Cement Hydration on the Millisecond Timescale

“…[9][10][11] Polycarboxylate ethers (PCEs) are commonly used superplasticizers because of their strong dispersion effect. [12] The focus of previous studies was usually on the change of the rheological behavior of the cement paste and the key factors of the PCE adsorption process. [13][14][15][16][17][18] The formation of the hydrate phases is often interpreted based on the change of fluid behaviors and zeta potentials, but not characterized by analyzing the crystallization processes directly.…”

“…The origin of the dispersion effect associated with PCE is frequently discussed in literature. [5,12,19] Their effect is mainly described based on charge and adsorption effects during the cement hydration. Zeta potential measurements indicate that the PCE polymer backbone adsorbs primarily at the surface of hydrates from the cement phase C 3 A.…”