Insight into the rheological performance of plasticized-cement paste containing a tailored comb-shaped polycarboxylate superplasticizers: molecular architecture and functionalizing

چکیده مقاله

This study deals with developing efficient comb-shaped polycarboxylate superplasticizers (PCs) with different molecular architectures as sustainable additives for mortar and concrete processing. The PC synthesis involved polycondensation of methacrylic acid (MAA) and methoxy polyethylene glycol (MPEG) with different molecular weights (750, 1000, and 2000 Da), followed by free-radical copolymerization of MAA, 2-acrylamide-2-methylpropane sulfonic acid (AMPS), hydroxyethyl methacrylate, acrylamide, and the attained MPEG-grafted macromonomer. Successful copolymerization and grafting were approved by employing H NMR, FTIR, and GPC. The performance of PCs was evaluated for their dispersing ability in cement paste (water/cement: 0.30, PC content: 0.25 wt.%) through the slump retention, fluidity, apparent viscosity monitoring, and rheological behavior of cement pastes via the Herschel–Bulkley model using shear stress versus shear rate diagrams to calculate the yield stress. It was found that the grafted and ungrafted copolymers based on MAA-AMPS (with mass ratio of MAA:AMPS of 50:50 wt%) display greater workability due to the higher negative charge density and better adsorption on cement particles owing to sulfonate (−SO₃⁻) and CONH₂ groups. So, slump values of 300 mm and 400 mm were attained by ungrafted and MPEG750-grafted MAA-AMPS copolymers, respectively. Furthermore, the findings demonstrated that longer MPEG side chains higher than 750 Da greatly weaken the dispersing ability due to the lower steric hindrance repulsive forces, lower electrostatic interactions, and more chain-folding. Moreover, the incorporation of 0.25 wt.% by weight of cement of MPEG750-grafted MAA-AMPS copolymer in cement pastes reduced the yield stress over than 90%. Consequently, the know-how for tailoring effective MPEG-grafted superplasticizers with great slump retention (400 mm), low viscosity (lower than 0.1 Pa·s at a shear rate: 10 s⁻¹), and low yield stress (2.22 e⁻¹⁴Pa), compared to industrial ones, was achieved. Accordingly, this attempt provides a beneficial insight into developing high-performance water-reducing superplasticizers, as a promising candidate for advanced greener cement-based materials.