The use of eco-friendly lignin as a cementitious material to improve the engineering properties of disintegrated carbonaceous mudstone

Disintegrated carbonaceous mudstone (DCM) is a fine grain with soil-like properties produced by disintegrating carbonaceous mudstone. Notably, DCM further disintegrates and softens when exposed to water and easily collapses under stress, undermining the long-term stability of DCM-filled embankments. In this study, the unconfined compressive strength (UCS), direct shear tests, disintegration test, mercury intrusion porosimetry tests (MIP), Fourier transform infrared spectra analysis (FT-IR), X-ray diffraction analysis (XRD), and Scanning electron microscope analysis (SEM) are used to examine the improvement of DCM in the Guangxi area through the introduction of lignin. The UCS of DCM modified by lignin (DCM/L) has been investigated under different curing conditions, lignin contents (1%, 3%, 5%, 7%, and 9%), and wet-dry cycles. The UCS of DCM/L increased significantly compared to untreated DCM and the UCS of DCM/L is less affected by the wet-dry cycle. The introduction of lignin can improve the cohesion of DCM, and lead to smaller mass loss and lower disintegration rate, confirming much better water stability of the DCM/L samples. The microscopic characterization results reveal that lignin can remarkably reduce the porosity and enhance the compactness of DCM. Moreover, lignin cements the DCM particles together through bonding, and the surface cation distribution of the clay minerals in the DCM is altered through ion exchange. The filling, bonding, and ion exchange capabilities of lignin are the main mechanisms for improving the strength of DCM.