Effect of molecular structure of maleic anhydride, fumaric acid – Isopentenyl polyoxyethylene ether based polycarboxylate superplasticizer on its properties in cement pastes

Polycarboxylate ether (PCE) superplasticizers with different molecular structure were synthesized by copolymerizing macro-monomer with cis-butenedioic anhydride (MAH) and trans-1,2-ethenedicarboxylic acid (FA). Gel permeation chromatography, specific charge density, Fourier transform infrared spectroscopy, 1H and 13C nuclear magnetic resonance were used to characterize these co-polymers. Their Ca2+ binding capacity, adsorption behaviors, retardation effects and dispersion efficiency were investigated by the calcium-ion selective electrode, total organic carbon, X-ray Photoelectron Spectroscopy, zeta potential, calorimetry measurements, mini-cone and rheological tests. Results indicated that PCE containing more FA possesses the higher density of –COO– groups, due to the higher reactivity of FA than MAH. The high density of –COO– groups in PCEs significantly affects their adsorption behaviors, retardation, and dispersion of cement pastes. Intermolecular chelation between –COO– groups and Ca2+ is dominated for FA-PCE, while the main coordination modes between –COO– in MAH-PCE and Ca2+ are intramolecular chelation owing to more adjacently distributed –COO– groups. FA-PCE exhibits larger adsorption amount and thicker adsorption layer compared with MAH-PCE. Hence, the FA-PCE demonstrated stronger dispersion efficiency, with which the cement pastes showed excellent flowability and rheological properties, correspondingly.