Dynamic mechanical performance of the concentrated solution sludge solidified by ground-granulated blast-furnace slag and municipal solid waste incineration fly ash geopolymer

A comprehensive understanding of the dynamic mechanical response of alkali-activated ground granulated blast furnace slag (GGBS) / municipal solid waste incineration fly ash (MSWI FA) solidified concentrated solution sludge (CSS) is of great significance for its engineering applications under different strain rate conditions. Unconfined compression strength (UCS) and split Hopkinson pressure bar tests were conducted on the solidified CSS to determine their static and dynamic strength. Moreover, XRD, FTIR, SEM, TGA, CT, MAS/NMR tests, and concentration tests of heavy metals and polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) were carried out to determine the hydration products, microstructure, geopolymer gel molecular structure, and contaminant immobilization effect of solidified CSS, thereby clarifying the solidification mechanism of alkali-activated GGBS/MSWI FA on the CSS from molecular scale to engineering scale. The results identify 15% MSWI FA as the optimum content for solidified CSS, corresponding to a 28-day UCS of 17.82 MPa. The dynamic strengths/dynamic increase factors (DIF) of solidified CSS with 15% and 20% MSWI FA are 17.68 MPa/1.0 and 19.39 MPa/3.2, respectively. The geopolymer hydration products are mainly geopolymeric gels and ettringite, with the formation of Friedel's salt. The geopolymeric gels are C-A-S-H, N-C-A-S-H and N-A-S-H. Excessive MSWI FA inhibits the formation of N-A-S-H and causes superfluous residual MSWI FA particles and closed pores in the solidified CSS, which is beneficial for inhibiting stress concentration and crack propagation, enhancing energy dissipation and improving the dynamic strength. Research findings of this study advance the resource utilization of the solidified CSS from static application scenarios to dynamic application scenarios.