Effect of calcined clay reservoir sediments on the behaviour of sustainable calcium sulfoaluminate-blended cements

Total world cement manufacture is estimated at 4.65 billion tons in 2016 and the annual CO2 emissions from cement plants reach almost 2.8 billion metric tons, representing about 7% of the global anthropogenic emissions. The use of alternative cements and supplementary cementitious materials (SCMs) represents a powerful tool for both reducing the CO2 footprint related to cement industry and producing more durable environmentally friendly materials. Calcium sulfoaluminate (CSA) cements are special hydraulic binders obtained from non-Portland clinkers; they are very interesting under both technical and environmental point of view. Pulverized coal fly ashes and blast-furnace slag are the major sources of SCMs which also include natural pozzolans, silica fume, rice husk ash and metakaolin. The efficiency of SCMs depends on their chemical composition, fineness and amount of amorphous phases. In this paper, it is investigated the possibility of using clay reservoir sediments (CCRS), calcined at 750°C, as SCMs in blended CSA cements; these binders were subjected to physico-mechanical and hydration tests for curing times ranging from 4 hours to 56 days. X-ray fluorescence and diffraction, differential thermal–thermogravimetric analyses and scanning electron microscopy were employed as characterization techniques. It has been found that CCRS are very interesting since their utilization as SCMs allows a clinker dilution, thus implying both a decrease of CO2 emissions and a reduction of costs related to CSA cement production; moreover the hydration behaviour and the physical- mechanical properties of CSA blended cements were positively affected by the addition of CCRS.