Comb Polymer Architecture Effects on the Rheological Property Evolution of Concentrated Cement Suspensions

Abstract

We have studied the rheological behavior of concentrated cement suspensions in the absence and presence of comb polymers comprised of a polyacrylic acid (PAA) backbone and charge-neutral, poly(ethylene oxide) (PEO) teeth. These species possessed a uniform backbone molecular weight and graft density, with varying teeth molecular weight. Both PAA, a linear polyelectrolyte, and PAA/PEO comb polymers imparted initial stability to concentrated cement suspensions above a critical weight fraction, w* of 4 mg/(g of cement). Cement-PAA suspensions, however, set prematurely. Their rapid, irreversible stiffening stemmed from deleterious interactions between PAA and multivalent counterions in solution. Interestingly, the presence of PEO teeth comprised of only a few monomer units in length mitigated such interactions. The rheological property evolution of concentrated cement-PAA/ PEO suspensions exhibited complex behavior ranging from the reversible gel-like response observed at short teeth lengths to a remarkable gel-to-fluid transition observed during the deceleratory period for systems comprised of longer PEO teeth. At longer hydration times, all cement-PAA/PEO suspensions exhibited initial elastic modulus values, G i ϳ exp(t/ c ) before the onset of the acceleratory period, followed by initial set. Their characteristic hydration time, c , and set time depended strongly on the concentration of "free" carboxylic acid groups [COO ؊ ] arising from non-adsorbed polyelectrolyte species in solution.

Microstructural changes of globules in calcium–silicate–hydrate gels with and without additives determined by small-angle neutron and X-ray scattering

“…The estimated mass losses due to the presence of adsorbed polymers (considered the baseline due to the degradation of the inorganic phase) are 0.4 ± 0.1% for CÀSÀH/PCE102-6 and CÀSÀH/PCE23-6 and 0.2 ± 0.1% for CÀSÀH/PCE102-2 and CÀSÀH/PCE23-2. These semi-quantitative observations are in agreement with the literature [4][5][6][7][8][9][10], confirming the higher propensity of the PCEX-6 series to be adsorbed on the calcium silicate phase, as a result of the higher amount of charged carboxylic groups present on the backbone.…”

“…These globules pack into a more open fractal structure compared with the higher side chain density sample (PCE102-2) and the pure CÀSÀH sample. This should be related to the fact that a PCE with a lower side chain density has a higher adsorption on the C 3 S starting powder as well as on the final CÀSÀH particles and hence affects more on the microstructure of CÀSÀH [4][5][6][7][8][9][10]. However, surprisingly, the PCE23-Y series (shorter PEO chain length) shows the reverse trend.…”

“…Each of these pieces can be tuned to produce several graft copolymers varying in the molecular weights and chemical structures. The effect of adding PCEs depends on the chosen chemical structure, which can dramatically alter the interaction between PCEs and the cement matrix [4][5][6][7][8][9]. The adsorption of the PCEs on the surface of the cement particles increases if the density or length of the PEO side chains is decreased.…”

“…While the influence of PCEs on the macroscopic observables of cement (rheology, mechanical properties, and hydration dynamics) has been reported in the literature [4][5][6][7][8][9], the change in the CÀSÀH microstructure due to the PCE additives remains mostly unknown. Very recently, we used small-angle neutron scattering (SANS) to study the microstructure of synthesized pure calcium-silicate-hydrate (I) gel (CÀSÀH (I)) [11].…”

Rheological behavior of PMN gels for solid freeform fabrication

“…In the second approach, the pH of the system was reduced below pH 9 to obtain a strong gel network. Since the ionization of PAA molecules is very sensitive to the variations in the suspension pH and the hydrodynamic radius of PAA decreases as the pH decreases [29,30]. In the last method, monovalent and divalent salts were introduced to the system and their ability to construct a gel network was evaluated.…”