Effect of secondary copper slag as cementitious material in ultra-high performance mortar

• The increase of copper slag content enhances the workability of the fresh UHPM.
• The increasing SCS fineness is more effective for strength enhancement than QCS.
• High dosage of Glenium 51 and presence of Zn cause a delay of the cement hydration.
• The Ca ion consumption by finer copper slag is more than for coarser ones.
• The CaO-poor and SiO2-moderate slag tends to consume limited amount of portlandite.

This research investigates the use of copper slag as supplementary cementitious material (SCM) in ultra high performance mortar (UHPM). Two secondary slag types from a plant in Belgium were utilized as SCM and were classified as a quickly cooled granulated copper slag (QCS) and a slowly cooled broken copper slag (SCS). Both materials were ground intensively using a planetary ball mill. A low water-to-binder ratio of 0.15 was chosen for the UHPM in this study. Various mortar and cement paste samples were produced with increasing copper slag content from 0 to 20 wt% in steps of 5 wt%. Particle size distribution (PSD) and specific surface area (SSA) of the copper slag were assessed using laser diffraction and the Blaine permeability test. The pozzolanic activity of copper slag was evaluated using the Chapelle test, strength activity index (SAI) and Frattini test.The results obtained, showed that the strength of mortars with different copper slag proportions was comparable to or even better than the control mixture at 90 days. The increased fineness of the copper slag enhances the mortar strength. Using isothermal calorimetry, it was found that the addition of copper slag slows down the hydration of the cement pastes. The rate of pozzolanic activity of copper slag depends on temperature, curing age, and particle sizes.