Strength evolutions of varying water content-dredged sludge stabilized with alkali-activated ground granulated blast-furnace slag

Abstract

The variation of water content significantly affects the strength development of stabilized dredged sludge (DS), as well as the rational use of binder. This paper experimentally studies the strength and microstructure evolutions of DS stabilized with alkali-activated ground granulated blast-furnace slag (GGBS) under different water contents, via a range of unconfined compressive strength (UCS), X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests. The sodium hydroxide (SH) and sodium silicate (SS) were used as single and composite activators for GGBS, and their roles on the stabilization efficacy were mainly focused. The results illustrated that the optimum single activator content tended to increase with the increase of water content. Composite activators were more effective than single activator in activating GGBS for achieving higher UCS of stabilized DS. The optimum mass ratio of SH to SS (H/S) in composite activators was 2/3, 2/3 and 1/4 at water content of 60, 70 and 80%, respectively. The linear empirical equations for predicting 60- and 90-day UCS based on 28-day UCS were proposed. XRD and SEM results confirmed that calcium silicate hydrate and calcium aluminate hydrate were the major hydrations, which undertook the cementation and filling roles. Furthermore, the micro-mechanisms revealing the strength evolutions of stabilized DS were analyzed and discussed. The results recommended that using 20% SH/SS-GGBS binder with optimum H/S of 2/3, 2/3 and 1/4 as the substitute of equivalent PC for stabilizing DS with water content of 60, 70 and 80%, respectively.