Impact of Slags Contained in Blended Cement on Dispersing Effectiveness of PCEs
Ahmad Habbaba and Johann Plank
Appears on pages(s):
adsorption; anionic charge amount; polycarboxylate; pore solution; portland slag cement; superplasticizer; zeta potential
In portland slag cements (PSC), different slag compositions can produce variations in workability due to the disparity in the surface chemistry of the slags. Here, the surface chemistry of different PSCs dispersed in water was studied in the absence and presence of polycarboxylate (PCE) superplasticizers. Six PSCs were prepared by mixing portland cement with 30 or 70 wt.% of three slags. As PCEs, two copolymers based on methacrylic acid–co–?–methoxy poly(ethylene glycol) methacrylate ester were employed. It was found that the slags sequester ions from the pore solution, namely Ca2+ and SO42- ions forming an electrical double layer on the slag surface. Zeta potential measurements confirmed that different slags can exhibit different surface charges which can strongly affect PCE adsorption. The differences in the amounts of PCEs adsorbed result in different dosages required to achieve comparable dispersion. Generally, all slag cements tested required less PCE to achieve the same fluidity as with neat cement.