Packing Versus Binding of Mineral Particles in Hardened Cementitious Pastes: Revisiting Strength-Toughness Relationship Subjected to Filler Effect

Abstract

Reactive solids embedded in cementitious composites can leverage both packing and binding, which act distinctly in determining the composite strength and toughness. Here, the individual and coupled behaviors of particle packing versus binding are investigated in hardened cementitious pastes (HCP), aiming to understand their physiochemical interplays to inform rational use of filler materials. The actions of cement hydration, pozzolanic reaction, and pore densification were examined separately, and the resultant influences on the compressive strength (f_c), tensile strength (f_t), and mode I fracture toughness (K_IC) were characterized. Results show that inert packing (up to 30 vol%) promoted f_c, f_t, and K_IC, while the improvement in K_IC became increasingly limited at high packing densities. Contrastingly, reactive particles produced consistently higher K_IC by enhancing particle binding. Our discussion highlights the following toughening mechanisms associated with filler effect: 1) a narrow particle spacing induced by a large filler volume makes it easier to bind adjacent particles without raising total cementitious content; 2) pozzolanic reaction reduces weak portlandite interfacial planes, demonstrating a greater toughening efficiency than cement hydration. These findings shed light on effective strategies for controlling HCP’s strength-toughness relationship and offer references for selecting emerging natural and recycled mineral resources for value-added construction applications.