Investigating the carbonation kinetics of the ternesite-belite-rankinite multi-component carbonatable binder system: Optimizing performance for industrial products

Abstract

Ternesite (C₅S₂$), reported as an ultra-low lime carbonatable binder, has demonstrated significant competitive advantages. This study prepared a novel carbonatable binder (NCB) mainly composed of ternesite, belite, and rankinite on a rotary cement kiln production line, aiming to investigate the influence of water-to-solid (w/s) ratio, CO₂ pressure, and carbonation duration on the compressive strength, carbonation kinetics, and phase evolution of NCB. The results indicated that an increase in the w/s ratio initially enhanced, but subsequently decreased, both the compressive strength and the degree of carbonation of NCB. Carbonation kinetics shifted from being controlled by the diffusion rate of Ca²⁺ to that of CO₂, with carbonation products evolving from polycrystalline calcium carbonate to predominantly calcite. As CO₂ pressure increased, the compressive strength initially increased before declining, although the degree of carbonation consistently increased. The influence of CO₂ diffusion rate control diminished, and the carbonation products shifted towards calcite as well. The optimal w/s ratio ranged from 0.15 to 0.2, with the CO₂ pressure should remain below 0.2 MPa. Among them, the w/s ratio exerted a more pronounced impact on the compressive strength and carbonation kinetics of NCB. Additionally, a w/s ratio exceeding 0.25 favored the carbonation of C₅S₂$, whereas increased CO₂ pressure proved advantageous for β-C₂S carbonation. This study provides theoretical support for the industrial production and carbonation curing process control of NCB products.