Structure-property study of novel star-shaped block polycarboxylate superplasticizers prepared via ATRP in Portland cement

Star-shaped superplasticizers exhibited excellent dispersion performance on cement paste , but the molecular structure remained poorly controlled. This study develops three star-shaped block superplasticizers via atom transfer radical polymerization to investigate their effects on fluidity and early hydration in the Portland cement system. The three star-shaped block superplasticizers with acid to ether monomer ratio of 28, 36 and 100, are marked as SPCE-1, SPCE-2 and SPCE-3 respectively. Fluidity test shows that SPCE-1 and SPCE-3 with higher hydrodynamic radius exhibit better initial fluidizing effect than SPCE-2. Besides, there is competitive adsorption of SPCEs between the clinker phase and nano-ettringite in pore solution. SPCE-1 behaves best in fluidity retention due to the increase of adsorption amount over hydration time. A dispersion mechanism based on the extended-DLVO theory was proposed that SPCEs reduce hydrophobic interaction between cement grains and prevent agglomeration between cement grains and air bubbles.