Study on the Impact of Na/Ca Bentonites on the Dispersion Performance of Conventional and Modified Phosphate Polycarboxylate Superplasticizers in Cement Mortar

Through molecular structure design, modified polycarboxylate superplasticizers (PCEs) were synthesized via copolymerization using isoprenyl oxy poly(ethylene glycol) ether (TPEG), acrylic acid, and hydroxyethyl methacrylate phosphate. TPEG-PCEs were selected as potential dispersants for Na/Ca-bentonite containing cement mortar. Other two kinds of commercial PCE that were obtained based on methallyl ether (HPEG) and ethylene-glycol monovinyl polyethylene glycol (EPEG) as macromonomers were also applied in the mortar. The effects of the type of bentonite and its dosage, as well as the monomer structure of PCEs and the type of cement, on the dispersion properties of the bentonite-containing mortar were studied. According to the findings, the initial fluidity of the mortar was reduced by about 20 mm when two kinds of bentonite were used. Applying 3% Ca-bentonite resulted in 40% flow loss in the mortar after 1 h. The fluidity of the mortar with Na-bentonite exhibited lower dispersion ability than that with Ca-bentonite when HPEG-PCE and EPEG-PCE were chosen as dispersants. The TPEG-PCE exhibited superior dispersing performance over HPEG-PCE and EPEG-PCE and exerted a retarding effect on cement, being also weakly sensitive to clay content. Thus, TPEG-PCEs with phosphate groups present a viable alternative to conventional PCEs.