Which factors impact the effectiveness of PCEs in alkali-activated slag cements?

Abstract

Behavior of different PCEs (MPEG (methacrylate ester), HPEG (methallyl ether), EPEG (2-hydroxyethyl poly(ethylene glycol) vinyl ether) based PCE) in NaOH-/Na₂SiO₃-activated two-part slag binders was investigated. In both activator solutions their solubility follows the order MPEG$>$$>$HPEG$>$$>$EPEG according to “cloud point” method. GPC chromatograms confirmed that at RT all PCEs don't decompose in activator solutions, independent of activator concentration and exposure time (1h/1d). “Mini-slump” tests confirmed the highest dispersing effectiveness of HPEG PCE, and the least for MPEG PCE. No PCE could disperse Na₂SiO₃-activated slag when PCE was dissolved in mixing water. Adsorption tests demonstrated non-Langmuir behavior in NaOH and almost no adsorption in Na₂SiO₃ pastes. DLS measurements revealed that in 1–2 M NaOH and 0.25 M Na₂SiO₃, decreased steric size (R_h) of PCE molecules was noted, indicating the coiling of PCE polymers. At very high activator dosages (3 M NaOH and 1 M Na₂SiO₃), remarkably increased R_h values due to the agglomeration of several PCE molecules was observed. Apparently, PCE effectiveness in AAS is strongly controlled by its solved conformation in AAS pore solution.