Bio-derived Kraft Lignin as a Green Stabilizer for Surfactant-assisted Nano Silica Dispersion in Cementitious Systems

This work explores the potential of Kraft Lignin-modified nanosilica (KL-NS) as a sustainable additive for cementitious composites, comparing its performance with both PCE-based nanosilica and plain OPC. The investigation combined microstructural analysis of pore features and hydration products with macro-scale measurements of compressive strength, ultrasonic pulse velocity (UPV), and electrical resistivity, supported by statistical validation. The inclusion of KL-NS led to a denser, more homogeneous matrix by accelerating hydration, consuming portlandite, and promoting greater C-S-H gel formation. Clear refinements in pore structure were observed: compared to OPC, the critical, average, and median pore diameters decreased by about 31-32%, while total porosity dropped by 21%. Even when benchmarked against PCE-NS, the KL-NS blends displayed a finer pore network and lower porosity, underlining its effectiveness in dispersing nanosilica and stabilizing hydration products. These structural improvements translated into notable performance gains. At 90 days, compressive strength rose to 58.2 MPa, representing increases of 40% over OPC and 9% over PCE-NS. UPV and resistivity also climbed to 5480 m/s and 27.8 kOhm.cm, which were 41% and 41.1% higher than OPC, respectively. All differences were statistically significant (P < 0.001). Alongside these technical benefits, Kraft Lignin's renewable and bio-based nature positions it as an eco-friendly substitute for synthetic dispersants, offering a path toward more durable and sustainable cementitious composites.