Pozzolanic behaviour and environmental efficiency of heat-treated fines as a partial cement replacement in mortar mixes

This study assessed the suitability and environmental efficiency of a heat-treated fines (HTF) material, a by-product from contaminated soil heat-treatment, to optimize the percentage by weight (wt.%) replacement of cement to produce lower embodied carbon cement mortar for the construction industry. Here, HTF replaced Portland cement at rates of 10, 20, 30 and 40 wt% in mortar mixes. The composition, workability, water uptake and 7- and 28-day strengths of the mortars was experimentally assessed. These results were used to calculate an environmental efficiency metric, assessing the embodied carbon based upon their mix formulation and strength. Results show that cement replacement up to 30 wt% attained compressive strengths >40 MPa (>90 % of control), while 40 wt% HTF reached compressive strengths >40 MPa with the use of a cement superplasticiser, but at the cost of increased embodied carbon due to the superplasticiser. A decrease in portlandite content with heat-treated soil fines content was observed using infrared spectroscopy, X-ray diffraction and thermal analysis, confirming that HTF underwent pozzolanic reactions. Environmental efficiency metrics showed that 30 wt% HTF in the mixes resulted in up to a 18 % reduction in embodied carbon per unit strength than conventional OPC.