Thixotropic structural build-up of cement-based materials: A state-of-the-art review

Thixotropic structural build-up is an intrinsic property of fresh cementitious materials, playing a significant role in pumpability, stability and formwork filling of concrete, as well as buildability in 3D printing. This paper presents a critical review on the thixotropic structural build-up of cement-based materials from the viewpoints of origins, evaluation methods, influencing factors and applications. Recent research indicates that the origin of structural build-up of cementitious materials is a combining result of colloidal interactions and chemical hydration, with three stages of colloidal network percolation, rigid percolation and rigidification. The evolution of static yield stress and storage modulus can be used to evaluate the structural build-up of fresh cementitious materials, each describing different aspects. Increasing particle volume fraction, decreasing surface coverage and reducing maximum packing fraction exhibit a positive effect on the increase in the structural build-up. Based on the relationships with performance parameters, the thixotropic structural build-up can be used to predict formwork casting, numerical simulations and 3D concrete printing. Furthermore, on-demand stiffening can be obtained by magneto-controlled structural build-up of cementitious materials containing magnetizable particles.