Assessment of packing, flowability, hydration kinetics, and strength of blended cements with illitic calcined shale

•Illitic calcined shale have great potential as low-energy and low-carbon SCM.•The packing density of blended cement paste decreases, but it increases for mortar.•The flowability depends on the particle size distribution and the specific surface area.•Blended cements with illitic calcined shale show the CH-reduction and the pore size refinement.•The compressive strength of blended cements is higher than the OPC mortar 90 days.