Understanding the Impact of KNO3 on the Carbonation Behavior of γ-C2S

γ-dicalcium silicate (γ-C2S) has received little attention in engineering applications due to its low hydraulicity, but it exhibits high carbonation reactivity and rapid strength gain with the added benefit of CO2 absorption, which demonstrates a vast potential for application in building materials. Included herein is an investigation of the promotion impact concerning a potassium nitrate (KNO3) solution on the carbonation behavior of γ-C2S, including the degree of carbonation (DOC), microstructure, and mechanical properties. Results show DOC increases when KNO3 is introduced into the system, and as the concentration of KNO3 solution rises, DOC can reach as high as 60%, compared with 49% without KNO3; The porosity of the system is reduced by 37%; The compressive strength after 24 h of accelerated carbonation, with the KNO3 concentration of 2 mol/L, reaches 90 MPa—34% higher than that of the blank group. The presence of KNO3 solution contributes to retaining water—the dominant position for carbonation—in the sample and reducing evaporation, thus prolonging the carbonation time. The increased volume of carbonation products densifies the whole system as the reaction occurs. A barrier to γ-C2S dissolution, the amorphous silica layer wrapping on the surface of grains, is destroyed due to the introduction of K+, facilitating the continuous dissolution of silicate. The incorporation of KNO3 results in a larger crystal in size and more regularity in shape. Prolongation of the reaction duration allows for more adequate crystal growth, resulting in compacts with superior mechanical properties.