Synthesis of kaolin-based alkali-activated cement: carbon footprint, cost and energy assessment

The main purpose of the work reported herein is to use kaolin to produce one-part alkali-activated cement. Thermal activation was performed on kaolin in the presence of alkalis (calcium oxide, sodium silicate, and sodium carbonate). Optimization experimental investigations were undertaken with selected alkalis to maximize the mechanical properties as well as minimize the cost of the resultant alkali-activated cement. Scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) test techniques were used to get insight into the binder chemical phases and their microstructure. The results showed that the optimal formulation for the alkali-activated kaolin cement developed consists of 62.5 wt.% kaolin, 30 wt.% calcium oxide, 5 wt.% sodium carbonate and 2.5 wt.% sodium silicate. The 7-day compressive strength at heat and room-curing temperatures reached 19.83 and 16.47 MPa, respectively. The competitive merits of the kaolin-based cement assessed against Portland cement considering the raw materials and production processing contributions to carbon footprint, cost, and energy content. The carbon footprint of the alkali-activated kaolin cement was 70% less than that of Portland cement. The cost and energy content of the alkali-activated kaolin cement was 45% and 70%, respectively, less than those of Portland cement.