Atomic-level insights into pore refinement of cement-based materials via CO2-to-CaCO3

DH Zhu and L Zhang and ML Nehdi and JF Zhang and L Wang and SJ Zhang and HS Jin, CONSTRUCTION AND BUILDING MATERIALS, 492, 143073 (2025).

DOI: 10.1016/j.conbuildmat.2025.143073

Cementitious binders, characterized by their porosity and high content of portlandite, are capable of reacting with CO2 to produce carbonate compounds that possess binding properties. This study explores the carbonation curing process in cement-based materials, where CO2 reacts with cement to form CaCO3, using molecular dynamics and density functional theory simulations. The focus is on analyzing the effects of pore size, humidity, and temperature on CO2 diffusion, adsorption, and reaction efficiency. Results show that larger pores (e.g., 24 & Aring;) enhance CO2 consumption, with ratios of 0.334 and 0.381 under dry and humid conditions, while smaller pores (e.g., 8 & Aring;) limit CO2 entry. Additionally, water molecules under humid conditions significantly hinder CO2 diffusion, with the self-diffusion coefficient decreasing by approximately 30 % compared to dry conditions. However, larger pores alleviate this hindrance, providing an additional diffusion pathway for CO2. Although increasing the temperature (up to 700 K) enhances CO2 diffusion, it reduces the adsorption rate, leading to a significant decrease in the CO2 consumption ratio. The study also develops a linear regression model between CO2 consumption ratio and the square root of time, further revealing the kinetic characteristics of CO2 consumption during the carbonation curing process. The reaction between CO2 and Ca(OH)2 is thermodynamically spontaneous under both dry and humid conditions, with the Gibbs free energy being lower in the humid environment, indicating that water molecules stabilize the reaction products and enhance the carbonation reaction at low temperatures. These findings provide important theoretical support for optimizing the carbonation curing process, contributing to the improvement of concrete performance and the reduction of the carbon footprint in the cement industry.

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