Recycling concrete waste through a thermal treatment approach is a promising eco-friendly solution against CO2 emissions related to the cement industry. Various researchers have treated laboratory-produced hydrated cement fines (HCFs) at different intermediate temperatures to produce thermally reactivated cement fines (RCFs) and highlighted the recycling possibilities by recovering the essential strength-forming clinker phases. RCFs are known for their loose and porous particle morphology, which has an adverse effect on their workability and mechanical strengths. This research intends to improve the particle morphology as well as the physico-mechanical properties of RCFs with the addition of ground blast furnace slag (GBFS). 28-day hydrated cement specimens (HCS) are crushed to particle sizes of <2 mm to produce hydrated cement fines (HCFs). HCFs are treated in an electric furnace at 700 ℃ to produce thermally reactivated cement fines (RCF-700 ℃). RCF-700 ℃ (<2 mm) are replaced with 25 wt.% and 50 wt.% of GBFS. The mixtures of RCF-700 ℃ and GBFS are milled using a planetary ball mill and sieved to achieve a particle size of <250 µm. The results indicate that RCF-700 ℃ – GBFS samples show improved particle fineness, lower water demand, lower porosity and enhanced compressive strength as compared to 100% RCF-700 ℃.