Cement composition effects on the rheological property evolution in concentrated cement-polyelectrolyte suspensions

We have studied the rheological property evolution and hydration behavior of white and ordinary portland cement (type I) pastes and concentrated cement-polyelectrolyte suspensions. Cement composition had a marked effect on the elastic property evolution (G′(t)) and hydration behavior of these suspensions in the presence of poly(acrylic acid)/poly(ethylene oxide) copolymer (PAA/PEO), even though their affinity to adsorb such species was nearly identical. Both white and ordinary portland cement pastes exhibited G′ ₀ values of ∼10 ⁴ Pa and fully reversible G′(t) behavior until the onset of the acceleratory period (t = 2 h), where the pastes stiffened irreversibly. In contrast, cement-PAA/PEO suspensions exhibited G′ ₀ values of ∼1 Pa and G′(t) behavior comprised of both reversible and irreversible features. Interestingly, ordinary portland cement-PAA/PEO suspensions experienced a gel-to-fluid transition on high shear mixing at short hydration times (<1 h), and the particle network did not rebuild until ∼24 h of hydration. In sharp contrast, white portland cement-PAA/ PEO suspensions remained weakly gelled throughout the initial stage of hydration even after high shear mixing. At longer hydration times (>1 h), both cement-PAA/PEO suspensions exhibited G′ _i(t) ∼ exp(t/τ _c) with τ _c values of 5.6 and 1.3 h for ordinary and white portland cement, respectively. Our observations suggest that hydration phenomena impact interparticle forces during early stage hydration and, ultimately, lead to initial setting through the formation of solid bridges at the contact points between particles within the gelled network.