Utilization of Lignin Residue as a Supplementary Cementitious Material with Potential for Carbon Reduction

Cement production is a significant source of CO₂ emissions, and reducing its carbon footprint is critical. Utilizing lignin residue as a supplementary cementitious material offers a promising strategy to lower carbon impact through clinker replacement and enhanced carbonation potential. This study used untreated lignin residue as a partial cement replacement to assess its effects on concrete properties and potential for carbon reduction, which remain largely unexplored. Four concrete formulations were prepared with 0–7.5 wt% cement replaced by lignin: CC (0%), C25 (2.5%), C50 (5%), and C75 (7.5%). Specimens were cast for mechanical strength, porosity, air and water permeability, and carbonation tests. Porosity decreased with higher lignin content, especially at 91 days. At this age, CC had a porosity of 10.82 ± 1.06%, while C75 recorded 6.84 ± 0.64%. At 28 days, lignin reduced air permeability, with CC showing 37.53 ± 3.33% and C25 23.93 ± 0.39%. In carbonation tests, lignin-containing concretes exhibited greater gas penetration depth, with values of 1.19 ± 0.21 mm for CC and 3.47 ± 1.09 mm for C75 after 147 days of exposure. Regarding carbon capture, partially replacing cement with lignin can help remove CO₂ from the atmosphere, with C75 being the most efficient.