Effectiveness of waste steel slag powder on the strength development and associated micro-mechanisms of cement-stabilized dredged sludge

Abstract

Waste steel slag is an industrial by-product during the process of steelmaking, and it is usually stacked in steelmaking plants. Employing steel slag in treating dredged sludge (DS) would be an economic and environmental protection solution. This study investigated the effectiveness of steel slag powder (SSP) on the strength development of cement-SSP-stabilized DS (CSDS). The effects of cement content and type, SSP content, humic acid (HA) content and curing age on the strength development of CSDS were analyzed via a series of UCS and pH tests. Additionally, microstructure analyses were conducted by scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. The results indicated that the cement content and type significantly affected the strength gain of CSDS. The UCS of CSDS increased first and then decreased with an increasing in SSP content. The SSP content of 5–10% was the optimal to improve the strength of CSDS, but for CSDS containing HA, the 15–20% SSP was recommended as cement admixture. The HA seriously reduced the strength of CSDS, but this strength loss can be effectively relieved by adding SSP. Based on the strength difference (ΔUCS) and strength growth rate (UCSgr), it was suggested that using 15% cement admixed 20% SSP was the most effective to the long-term strength development of CSDS. The variation of UCS with pH exhibited oscillation characteristics, and the pH of 9.00–10.00 was conducive to the strength development of CSDS. The microstructural analyses confirmed that the addition of SSP can contribute to the formation of cementitious products in CSDS, especially needle-like gel ettringite, and then leading to a dense inter-locked structure in CSDS.