Characterization of a mortar made with cement and sludge from the light-emitting diode manufacturing process

• The proposed method provides a new application of reused LED sludge as a resource.
• LED sludge powder contains nano-SiO2 particles and is a pozzolanic material.
• LED sludge enhances the mechanical properties of cement mortar.
• Sludge-blended cement mortar has superior strength relative to plain cement mortar.

This study uses sludge, which is a by-product of the light-emitting diode (LED) manufacturing process and an industry waste (called LED sludge), to replace some weight percentage of cement. The LED sludge powder was used to replace 5, 10, 20, and 30 wt.% of the cement, and the (5 × 5 × 5-cm3) sludge-blended cement mortar (SBCM) specimens were molded for a compressive strength test and other engineering property tests. The properties of the LED sludge sample were checked using a scanning electron microscope/energy dispersive X-ray spectrometry (SEM/EDS) analysis, an X-ray diffraction (XRD) analysis, and a solid-state nuclear magnetic resonance spectroscopy (NMR) analysis. The compressive strength test shows that the SBCM specimens have comparable compressive strength relative to ordinary Portland cement mortar (OPCM) specimens in the early curing age of 1–7 days, and 103–115% of the compressive strength of OPCM specimens after curing for 14–90 days. The test results reveal that the nano-particles promoted the pozzolanic reaction and enhanced the strength evolution. LED sludge can be converted into a useful resource by exempting the difficulty of disposal problems and appealing to the environmental sustainability.