The underlying role of sodium tripolyphosphate on the cementitious mechanism of calcium carbonate binder

Abstract

Calcium carbonate binder is well-known to reduce the carbon footprint and brings great economic and environmental benefits. However, the cementitious mechanism is unclear due to raw material diversity. We prepare calcium carbonate crystalline polymorphs-vaterite and calcite in the presence of sodium tripolyphosphate (STPP), and the cementitious mechanism is revealed. Herein, the optimal colloidal structure with vaterite as the binding phase is obtained at 5% STPP and the 1d compressive strength reaches 16.99 MPa. The cementitious property can be attributed to the crystallization transformation of amorphous calcium carbonate (ACC) and the electrostatic attraction of particles. In the cementitious process, the effect of STPP on the polymorph selection is determined by STPP contents. At low contents (＜5%), STPP is more effective in inhibiting the nucleation and growth of calcite than vaterite. At high contents (＞5%), calcite is entirely inhibited while the formation of vaterite takes place on the surface of bulk ACC through the coupling mechanism of dissolution-recrystallization and solid-state growth. These results shed light on the function of STPP during calcium carbonate biomineralization and the cementitious mechanism can help for preparing low-carbon calcium carbonate binder.