Effect of water to binder ratio on carbonation behavior of a novel carbonatable belite-ternesite binder

Abstract

The development of carbon capture, utilization and storage allows non-hydraulic low-lime calcium silicates capable of CO₂ activation to serve as a sustainable alternative binder. However, the diffusion and transport mechanism of CO₂ in these carbonation mediums are crucial for carbonation reaction, which heavily relies on the pore structures closely related to the water–binder ratio (w/b). This study focused on the role of w/b ratio (varying from 0.1 to 0.18) on the carbonation behavior of a carbonatable belite (β-C₂S)-ternesite (\({\text{C}}_{{5}} {\text{S}}_{{2}} {\overline{\text{S}}}\)) binder prepared with 100% municipal solid waste incineration residues upon carbonation curing conditions of 65% RH, 20% CO₂ concentration, and a temperature of 20 °C. The mechanical properties, microstructure, CO₂ uptake, and phase assemblage of this binder were evaluated. The results showed that the compressive strength and CO₂ uptake were increased with increasing w/b ratios from 0.1 to 0.14, which promoted the consumption of β-C₂S and \({\text{C}}_{{5}} {\text{S}}_{{2}} {\overline{\text{S}}}\), leading to an increased production of calcite. At up to 0.18, however, water overflow occurred, resulting in an approximately 78% decrease in the compressive strength. Also, increasing the w/b ratio changed the volume fraction of various pore size, particularly the predominance of large capillary pores that were beneficial to CO₂ diffusion. BSE images showed that silica gel tended to distribute around the unreacted particles, while CaCO₃ preferred to accumulate in the outside space.