Concrete Incorporating a Spent CO₂ Absorbent: Comprehensive Assessment of Microstructure, Strength, and Durability

Area of Science:

• Materials Science
• Environmental Engineering
• Civil Engineering

Background:

• Sustainable recycling of spent CO2 absorbents from direct air capture (DAC) is crucial for carbon capture technologies.
• Investigating the use of spent alkaline CO2 absorbents as a partial replacement for mixing water in cementitious materials.

Purpose of the Study:

• To evaluate the feasibility of recycling spent CO2 absorbents in cement.
• To assess the impact on microstructure, mechanical properties, and durability of cementitious materials.

Main Methods:

• Preparation of mortar and concrete with 0-40% absorbent replacement.
• Microstructural analysis (SEM, XRD, TGA).
• Mechanical testing (compressive and flexural strength).
• Durability assessment (freeze-thaw, acid resistance, carbonation).

Main Results:

• Low replacement ratios (10-20%) enhanced early-age strength via CaCO3 micro-filling and nucleation.
• Comparable long-term strength was observed at 10-20% replacement.
• Higher ratios (≥30%) led to detrimental effects: increased carbonation, C-S-H decalcification, porosity, and reduced strength.

Conclusions:

• Spent CO2 absorbents can be effectively recycled in cementitious materials.
• Optimal replacement range is 10-20% for beneficial effects.
• Higher replacement levels negatively impact cementitious material properties.