Application of dry composite electroplating sludge into preparation of cement-based decorative mortar as green pigment

• CEPS can be used as pigment to prepare decorative mortar.
• Mortars with CEPS have nearly same physical properties as these of the control.
• CEPS has not notably influence on the cement hydration.
• CEPS can densify the microstructure of mortar.
• Heavy metals immobilizing of mortars with CEPS can be more reliable.

The objectives of this study were to assess the feasibility of application of dry composite electroplating sludge (CEPS) into preparation of cement-based decorative mortar as green pigment, and to find a new disposal and resource approach for it. Color, water absorption, strength, hydration and leachability of cement-based decorative mortar are investigated. The results show that CEPS can adjust the mortar color well. Although CEPS leads to the increase of mortar water absorption, the water absorption of mortar prepared with 5% CEPS still meets the requirement stated in the Chinese Building Material Industry Standard JC/T 1024-2007. The mortars with CEPS are provided with nearly same compressive, flexural and tensile bond strengths as these of the control. Cement hydration products such as C–S–H gel, Ca(OH)2 and the entringite all can be observed in different specimens. The denser microstructures than that of the control are formed in the mortars with CEPS. It is found from almost similar intensity in Ca(OH)2 peak at 18.007° that CEPS has not notably influence on the cement hydration. It is also evident that heavy metal concentrations in leachates of the mortars with CEPS are far lower than recommended in the Chinese National Standard GB5085.3-2007. It is safe to people's health and environment that CEPS is recycled as green pigment to produce cement-based decorative mortar.