Effect of palygorskite on rheological behavior of cement paste and its microstructure regulation mechanism

Precise regulation of the rheological behavior of cement-based materials is crucial for advanced construction technologies such as 3D printing and underwater casting. Based on three types of palygorskite (PL) with distinct isomorphic substitutions, this study systematically investigates the influence and mechanisms of PL on the rheological properties, microstructural formation, and hydration kinetics of cement paste by combining water film thickness analysis, DLVO theory, a cohesion model, the Boundary Nucleation and Growth (BNG) model, and a series of experimental tests (e.g., setting time, fluidity, rheological measurements, and hydration heat). The investigation employs water film thickness analysis, DLVO theory, a cohesion model, and the Boundary Nucleation and Growth (BNG) model. The results indicate that at low dosages (≤0.5 wt%), PL enhances fluidity and shortens the setting time by optimizing particle packing and promoting the heterogeneous nucleation of C-S-H. Conversely, at high dosages (>0.5 wt%), PL forms a continuous three-dimensional network via "face-to-edge association," leading to a significant increase in yield stress, plastic viscosity, and cohesion, while simultaneously retarding the hydration process and reducing workability. Among the variants, PL with a moderate degree of isomorphic substitution (b-PL), characterized by an appropriate surface charge density, more readily forms the face-to-edge connected 3D network, demonstrating superior thickening and retarding effects. Furthermore, at high PL dosages, the cohesion force driven by ion correlation effects exceeds the predictions of classical DLVO theory and emerges as the dominant factor governing flocculation behavior. These findings provide a theoretical foundation for regulating the rheological properties of cement-based materials. • PL exhibits a unique dosage-dependent dual effect: ≤0.5 wt% enhances fluidity and shortens setting time, while >0.5 wt% acts as a potent thickener, significantly increasing yield stress and plastic viscosity. • At high PL content, the formation of a continuous 3D network via "face-to-edge" association is driven not only by classical DLVO forces but primarily by cohesion from ion correlation effects, exceeding classical theory predictions. • Cross-validation of water film thickness analysis, DLVO theory, a cohesion model, and the Boundary Nucleation and Growth model with experiments innovatively links PL's isomorphic substitution-governed microscopic interactions to macroscopic rheology and hydration kinetics. • These findings provide a theoretical basis for designing tunable cement-based materials, applicable to 3D-printed concrete and underwater casting.