Working mechanism of post‐acting polycarboxylate superplasticizers containing acrylate segments

Abstract

Acrylate-containing polycarboxylate superplasticizers were synthesized by copolymerizing acrylic acid, a-methallyl-xmethoxy poly(ethylene glycol) ether, and acrylic esters [hydroxyethyl acrylate (HEA) or hydroxypropyl acrylate (HPA)]. Their dispersing effects and fluidity-retaining capabilities were evaluated by spread tests of cement pastes. The temperature sensitivity of the performance was especially focused upon. It was found by Fourier transform infrared spectroscopy and specific anionic charge density measurements that the ester groups in the acrylate-containing copolymers hydrolyze in alkaline conditions, and thus additional RACOO 2 groups are continuously produced. The gradual production of RACOO 2 leads to increasing charge density and hence increasing adsorption of the polymer on the cement surface. The hydrolysis of HEA units is slightly faster than of HPA units in the corresponding copolymers. By this mechanism, a post-acting, or delayed, dispersing effect is realized. Such post-acting polymers alone or formulated with normal polycarboxylate superplasticizer can be used achieve a long fluidity retention of fresh concrete, especially under elevated temperatures.

The effects of nano‐C‐S‐H with different polymer stabilizers on early cement hydration

“…The number‐average molecular weight (M n ) and the polydispersity index (PDI) of the polymers are located in the ranges of 26 000‐35 000 and 2.13‐2.58, respectively, which are quite usual for radical polymerization. The actual molar ratio of the monomer units in the purified samples was characterized by 1 H‐NMR.As seen from Figure , The copolymerization ratio of AA to TPEG is about 8.34 and 2.34, which is slightly higher than the feeding ratio of 6 and 2 of the two monomers . This has been often reported because the polymerization rate constant of monomer AA is much higher than that of the macromonomers.…”

“…This has been often reported because the polymerization rate constant of monomer AA is much higher than that of the macromonomers. As a consequence, the actual content of the repeating unit AA in the synthesized copolymer is always higher than the designed monomer feeding ratio . The anionic charges of synthetic polymers are mainly contributed by the carboxylate and sulfonate groups in the polymer chains and thus are highly dependent on the pH value of the solutions.…”

“…The actual molar ratio of the monomer units in the purified samples was characterized by 1 H-NMR.As seen from Figure 4, The copolymerization ratio of AA to TPEG is about 8.34 and 2.34, which is slightly higher than the feeding ratio of 6 and 2 of the two monomers. 40,41 This has been often reported because the polymerization rate constant of monomer AA is much higher than that of the macromonomers. As a consequence, the actual content of the repeating unit AA in the synthesized copolymer is always higher than the designed monomer feeding ratio.…”

“…As a consequence, the actual content of the repeating unit AA in the synthesized copolymer is always higher than the designed monomer feeding ratio. 41,42 The anionic charges of synthetic polymers are mainly contributed by the carboxylate and sulfonate groups in the polymer chains and thus are highly dependent on the pH value of the solutions. It is well known that the carboxyl groups are fully deprotonated at pH value higher than 10.…”

Effects of crosslinked polycarboxylate superplasticizers with crosslinking agent containing ester and amide groups on the properties of cementitious systems

“…It is generally accepted that steric hindrance and electrostatic effects account for the mechanism through which superplasticizers promote the dispersion of cement particles. [1][2][3] Polycarboxylate superplasticizers are designed based on making a delicate trade-off between molecular structures and properties. A polyelectrolyte is usually used as the backbone chain of a superplasticizer while polyoxyethylene ether groups are employed as the sidechains.…”