Novel non-conventional raw materials as supplementary cementitious materials for low-carbon composite cement: Chemical reactivity, fresh and hardened state characterization

The incorporation of supplementary cementitious materials (SCMs) in cement-based construction is fast becoming an environmentally friendly option to reduce CO₂ emissions associated with cement production. Fifteen raw materials i.e. two conventional (blast furnace slag and fly ash) and thirteen non-conventional (fayalite slag, glass wool, stone wool, ladle slag, municipal solid waste incineration bottom ash, waste glass, high silicate mine tailings, high magnesium mine tailings, high alumina mine tailings, volcanic pozzolan Iceland, calcined Finnish clay, stainless steel slags, and precast concrete sludge) available in the Nordics were investigated as SCMs. The reactivity of the materials was compared using R³ test while the fresh and hardened properties of cementitious pastes with a 30% SCM replacement level were investigated via isothermal calorimetry, setting time, rheology, electrical resistivity, compressive strength, thermogravimetry and differential thermogravimetry (TG-DTG), x-ray diffraction (XRD), and scanning electron microscope coupled with energy-dispersive x-ray spectroscopy (SEM-EDS). The results showed that there exists a difference in the reactivities, and properties among the samples, attributed to the differences in the chemical and mineralogical composition of the SCM. Based on R³ test, blast furnace slag, fly ash, ladle slag, glass wool, stone wool, volcanic pozzolan Iceland, and calcined Finnish clay are classified as reactive materials (higher heat release and bound water) while the remaining SCMs are classified as inert or slow reacting materials. Strong correlations were found between chemical reactivity and paste properties as paste samples containing reactive materials as SCM performed better, exhibiting a reduction in setting time while having higher reactivity, compressive strength, electrical resistivity, and denser microstructure than those containing inert or slow reacting materials. Moreover, sustainable performance index based on the relationship between the availability and reactivity criteria of SCMs was developed.