Investigation on the strength, durability and swelling of cement- solidified dredged sludge admixed fly ash and nano-SiO2

The strength, durability and swelling behavior of cement-solidified dredged sludge (CDS) has been attracted more and more attention in recent years. This study performed a series of laboratory tests including unconfined compressive strength (UCS), water absorption, swelling tests and pH to investigate the effectiveness of using fly ash (FA) and nano-SiO2(NS) blended with Portland cement (PC) for DS solidification. Microstructural properties were also analyzed by conducting scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. The results showed that the addition of FA and NS can significantly improve the UCS of CDS. Using FA and NS together as PC admixture can effectively improve the water resistance. Compared with FA, NS was more effective to reduce the water absorption and swelling of CDS. Adding 0.9% NS to CDS notably reduced the 7-day water absorption and swelling value by up to 40% and 67.5%, respectively. Furthermore, the addition of NS is beneficial to control the pH level of CDS. The SEM and XRD results showed that CSH and CAH gels were the major cementitious products inside solidified DS. The addition of NS contributed to the formation of additional CSH gels in CDS.

Automated summary

This study investigates the effectiveness of using fly ash and nano-SiO2 blended with Portland cement for solidifying dredged sludge. The results show that the addition of fly ash and nano-SiO2 can significantly improve the strength and water resistance of the sludge, and reduce its water absorption and swelling. SEM and XRD analysis confirm the formation of cementitious products in the solidified sludge.