Mechanical behavior of fiber-reinforced, chemically stabilized dredged sludge

In order to improve the mechanical properties of dredged sludge, short polypropylene fibers were used as physical reinforcement, while cement and fly ash were used as chemical stabilizers. Different mass percentages of fiber (i.e., 0%, 0.05%, 0.1%, 0.2%, 0.4%, and 0.8%), cement (i.e., 15%, 20%, and 25%), and fly ash (i.e., 15% and 30%) were added to dredged sludge at two initial high water contents (i.e., 92% and 120%) and evaluated using physical experiments. The unconfined compression test was performed on samples after curing them for 28 days. The results show that inclusion of cement and fly ash can significantly increase the dry density and reduce the water content of dredged sludge after curing, consequently enhancing the unconfined compressive strength (UCS). It is found that chemical stabilization can increase the stiffness and brittleness of dredged sludge. However, excessively high fly ash fraction in the mix inhibits strength development in cement-stabilized dredged sludge. The inclusion of fiber decreases the initial stiffness and enhances the UCS, strain at failure, and residual strength of dredged sludge. The UCS increases with fiber content and then decreases slightly, with the optimal fiber content being 0.1%. Fiber reinforcement generates a distinct transition zone in the stress-strain curve, which enlarges with increasing fiber content. The contribution of fiber reinforcement to the strength of dredged sludge is more pronounced at relatively lower water content. The inclusion of fiber can temper the brittleness of chemical-stabilized dredged sludge with more ductile behavior by inducing a 'bridging' effect. This effect helps in reducing loading-induced cracking of the stabilized sludge.