Modification of nanoparticles for the strength enhancing of cement-stabilized dredged sludge

Abstract

This paper investigates the effectiveness of nano-modification on the strength enhancement of cement-stabilized dredged sludge (CDS). Three types of nanoparticles including nano-SiO2 (NS), nano-Al2O3 (NA) and nano-MgO (NM) were used as cement admixtures for dredged sludge stabilization. Effects of single nanoparticle content, mass ratio of composite nanoparticles and curing time on the strength development of CDS were evaluated via a series of unconfined compressive strength (UCS) tests. The pH evolutions of CDS caused by nanoparticles were also examined by a range of pH tests. Furthermore, micro-mechanisms reflecting the strength evolutions were analyzed by performing scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. The results indicated that adding nanoparticles can significantly improve the UCS of CDS. For single nano-modification, the optimum contents of NS, NA and NM were 4%–6%, 6% and 8%, which can increase the 7- and 28-d UCSs of CDS by 38% and 50%, 17% and 35%, 65% and 67%, respectively. Compared with single nano-modification, composite nano-modifications were more effective in improving the strength gain of CDS. The optimum mass ratios of composite nanoparticles, namely NS/NA, NS/NM and NA/NM, were 9/1, 3/7 and 3/7, respectively. Based on the strength growth rate, the composite nanoparticles with NS/NM of 3/7 were highly recommended. The addition of nanoparticles obviously affected the pH evolution of CDS, which was mainly determined by the difference of OH− production and consumption inside nano-modified CDS. The microstructural analysis revealed that C-S-H and C-A-H gels are the main cementitious products, and the addition of nanoparticles can obviously contribute to a denser and more homogenous microstructure of CDS.