Polyelectrolyte effects on the rheological properties of concentrated cement suspensions

Polyelectrolyte species, known as superplasticizers, dramatically affect th e rheological properties of dense cement suspensions, We have studied the i nfluence of sulfonated naphthalene formaldehyde condensate (SNF) and carbox ylated acrylic ester (CAE) grafted copolymers of varying molecular architec ture on the surface (e.g., adsorption behavior and zeta potential) and rheo logical properties of concentrated cement suspensions of white portland cem ent and two model compounds, beta-Ca2SiO4 and gamma-Ca2SiO4. The adsorption of SNF species was strongly dependent on cement chemistry, whereas CAE spe cies exhibited little sensitivity, The respective critical concentrations ( Phi*) in suspension required to promote the transition from strongly shear thinning to Newtonian flow (flocculated --> stable) behavior mere determine d from stress viscometry and yield stress measurements. Theoretical analysi s of interparticle interactions suggested that only colloidal particles in the size range of less than or equal to 1 mu m are fully stabilized by adso rbed polyelectrolyte species. Our observations provide guidelines for tailo ring the molecular architecture and functionality of superplasticizers for optimal performance.