Effect of Polycarboxylate Superplasticizer Modified by Sodium Hypophosphite on the Properties of β-Calcium Sulfate Hemihydrate

In this study, sodium hypophosphite (SHP) was used to modify polycarboxylate superplasticizer (P-PCE), and the properties of P-PCE on β-calcium sulfate hemihydrate (β-HH) were systematically investigated. The results showed that P-PCE could exhibit better fluidity and more retarding effect compared with the conventional polycarboxylate superplasticizer (C-PCE). The reason might be ascribed to the higher adsorption ability of P-PCE because of its stronger complexing capacity with calcium ion, which was induced by the phosphonate and phosphinate groups in the P-PCE molecule. Additionally, PCE played an important function in hindering the calcium sulfate dehydrate (DH) crystallization instead of the dissolution of β-HH, resulting in the retarding effect. This new type of PCE can show great potential in gypsum engineering.