Strength Properties of Cement-Stabilized Dredged Sludge Incorporating Nano-SiO2 and Straw Fiber

This study investigates the compressive and tensile strength properties of cement-stabilized dredged sludge (CDS) improved by straw fiber (SF) and nano-SiO2 (NS). The influence factors, including SF content, NS content, SF length, and curing time, were evaluated via a series of unconfined compressive strength (UCS, q(u)) and splitting tensile strength (STS, q(t)) tests. Furthermore, the microstructure evolutions and micromechanisms were explored by conducting scanning electron microscopy (SEM) tests. The results indicated that the inclusion of NS can obviously improve the UCS and STS of CDS, and the optimum NS content was 1.2%. Adding SF to CDS decreased its UCS but increased the STS. Compared with single SF or NS inclusion, the combination of SF and NS exhibited more advantage in improving the compressive and tensile strength behaviors. The optimum SF contents for NS-modified and SF-reinforced CDS (CNFDS) at 3, 7, 14, and 28 days were 0.5%, 0.4%, 0.3%, and 0.3%, respectively. Furthermore, 1.5% NS and 2-5 mm SF were the most effective in improving the UCS of CNFDS. The second-bearing effect occurred in the tensile stress-strain curves, in which the tensile stress evolution with strain was presented by a fitted linear equation. The optimum SF content, NS content, and SF length for CNFDS achieving the highest STS were 0.2%, 1.5%, and 5-10 mm, respectively. By fitting the relationship between UCS and STS, the relation of q(t) = 0.17q(u) for CNFDS was observed. The SEM analysis indicated that the interfacial friction and bonding between SF and cemented soil particles were mainly responsible for the strength properties improvement of CNFDS.