Pozzolanic reaction of a mortar made with cement and slag vitrified from a MSWI ash-mix and LED sludge

• MSWI ash-mix and LED sludge were melted to form a non-toxic slag.
• The strength of the slag-blended cement mortar (SBCM) is superior to OPCM specimen.
• SBCM reveals the greater strength by nano-particle effect and pozzolanic reaction.
• The proposed method provides an application of recycling MSWI ashes and LED sludge.

Fly ash and scrubber ash that were generated by incinerators were mixed to produce municipal solid waste incinerator (MSWI) ash mix based on the proportions of the produced ash. In addition, 50 wt.% sludge produced during the manufacturing process of light emitting diodes (LEDs) was mixed into the MSWI ash mix, which was then melted to create MSWI-LED slag. This slag was used to replace 0, 5, 10, 20, and 30 wt.% cement and then the 5 × 5 × 5 cm3 slag-blended cement mortar (SBCM) specimens were molded. Analyses of compressive strength and other properties were conducted. The results showed that the SBCM specimen at 1–7 days of age possessed a compressive strength close to or slightly higher than that of a ordinary Portland cement mortar (OPCM) specimen, whereas that at 14–90 days had a compressive strength 6–36% greater than that of OPCM specimens. The specimens were analyzed using X-ray diffraction (XRD), thermogravimetric and differential thermal analyses (TG/DTAs), and nuclear magnetic resonance (NMR). The results showed that the pozzolanic reaction in the slag increased compressive strength. Moreover, this study conducted a toxicity characteristic leaching procedure (TCLP) and investigated initial and final setting times and the fluidity of the specimens. The results indicated that MWSI-LED slag prevented heavy metal leaching, increased the compressive strength of specimens of different ages, shortened the initial and final setting times, and only slightly reduced fluidity. Replacing part of the cement in mortar with this slag facilitates waste recycling, enhances environmental protection, and meets the demand for sustainable development.