Research on the Mechanism of Humic Acid Effect on the Strength of Cement-cured Dredged Sludge

Abstract As an essential component of sludge, soil organic matter is also the most energetic component of the sludge solid phase. However, the organic content of sludge reduces the engineering qualities of cement-cured sludge and restricts the cement curing reaction process. Humic acid (HA) was employed in tests conducted indoors to mimic the organic material naturally present in the waste sludge. The effect of different HA and cement dosages was investigated for the strength of the dredged sludge. The mechanism of the effect of HA on the strength of cement-solidified dredged sludge (CDS) was examined in conjunction with the findings of unconfined compression strength (UCS), scanning electron microscopy (SEM), and X-ray diffraction (XRD). (1)The overall unconfined compressive strength of CDS decreased after the addition of HA. (2) The strength of the HA sludge-cured body exhibits an increasing trend with the increase in cement input. The strength of sludge cured bodies with high HA content can be enhanced by correctly increasing the curing agent. (3) HA acts as a cement retarder, delaying hydration time by adhering to the surface of cement particles to form an adsorption coating. (4) As observed by SEM, the conversion of C-S-H to foil-like is hindered by HA in the silt, and its microscopic morphology changes with the change of HA content, which is manifested by the decrease of CDS intensity on a macroscopic scale.