This study investigated the effect of the co-calcination temperature (600, 700, and 800 °C) and the blending ratio of green liquor dreg (GLD) and kaolinitic clay (2:1, 1:1, 1:2) to produce a limestone calcined clay (LC2)-type supplementary cementitious material (SCM). The phase assemblage and hydration process of composite cements comprising CEM I and varying replacement ratios (15 and 30 wt%) of the produced SCM were evaluated. An effective co-calcination temperature of 700 °C was identified considering the chemical reactivity of the LC2-type SCM determined by the rapid, relevant, and reliable (R3) testing. X-ray diffraction and scanning electron microscopy showed variations in the phase assemblage of the composite cements and the reference CEM I. Calcium carbonate from GLD and metakaolinite from the calcined clay contributed to the formation of carboaluminate in the composite cements, lowering its porosity. The 7- and 28-day compressive strengths of the mortars produced by replacing 15–30 wt% of the cement with this SCM, were comparable to those of the CEM I reference mortar. These findings demonstrate the industrial symbiosis potential between the paper and cement industries via applying co-calcination for resolving challenges for utilization of GLD, while producing a suitable kaolinitic clay based SCM.

DOI: https://doi.org/10.1016/j.cscm.2025.e04520