Optimizing ZnCl2-activated coffee ground biochar and MDEA for superior CO2 sequestration performance in sustainable cement mortar composites

초록

The cement industry is a major contributor to global CO2 emissions, creating an urgent need for carbon-sequestering construction materials. This study investigates the CO2 fixation performance of cement mortar incorporating coffee ground biochar and MDEA. Biochar in this study is produced at 500-900 °C with and without ZnCl2 activation, and characterized for density, water absorption, surface area, and CO2 uptake. Characterization reveals that ZnCl2-activated biochar at 900 °C achieves 687.71 m2/g surface area and 37.39 cm3/g CO2 uptake, substantially outperforming non-activated samples. Optimal biochars produced at 700-900 °C are incorporated into mortar at 3% cement replacement with 5% MDEA. Although fresh density and flow decrease with biochar addition, compressive strength at 28 days reaches 61.0 MPa for the 700 °C biochar mixture, representing a 21% increase over control. Isothermal calorimetry revealed delayed hydration kinetics with extended induction periods, while cumulative heat recovery at later ages explained the improved long-term strength. Combined biochar-MDEA mixtures exhibit synergistic CO2 fixation, with CaCO3 content reaching 4.26% compared with 0.87% for control. Volumetric CO2 fixation increases nearly fivefold to 18.17 kg/m3. Preliminary carbon balance for 1000 kg coffee waste demonstrates net CO2 reductions of 856-1256 kg, with high-temperature biochar providing 47% greater benefit through enhanced carbonation despite lower yield. These findings establish that the CGB-MDEA system represents a viable strategy for developing low-carbon cementitious materials that simultaneously valorize organic waste streams and enhance CO2 fixation. © 2026 Elsevier Ltd

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