Low -clinker cement prepared using circulating fluidized bed combustion ash

Limestone calcined clay cement (LC3) is a representative low-clinker and low-carbon cement that has received considerable attention. However, its use is largely restricted by the quality/distribution of the required clay resources and the energy consumption/CO2 emissions during clay calcination. Herein, a solid waste, named circulating fluidized bed combustion ash (CFBA), discharged by a circulating fluidized bed coal-fired power plant, which has compositions and properties similar to those of calcined clay, is proposed as a substitute for calcined clay in the preparation of low-clinker and low-carbon cement. In this study, the mix of the low-clinker cement based on CFBA was designed and optimized using Design Expert 13.0 software. The physical properties, hydration, hardened matrix structures, and carbon footprint of the low-clinker cement were investigated in detail. The results showed that the optimized mix design for low-clinker cement was 60 % clinker, 27.37 % CFBA, 7.379% limestone, and 5.251 % gypsum. In this case, the physical properties of the low-clinker cement were comparable to those reported for 42.5 grade LC3-50. The apparent activation energy of the low-clinker cement was 43.79 kJ/mol, indicating that the hydration reaction occurred more easily and the reaction rate was less sensitive to temperature than that of 42.5 grade ordinary Portland cement. The synergic hydration effect of the aluminum phase in the CFBA and limestone stabilized the AFt phase, refined the pore structure, and reduced the critical pore size of the cement matrix, thereby improving the later strength of the low-clinker cement. The embodied energy (EE) and embodied CO2 emissions (ECO2-e) of the low-clinker cement with 60 % clinker were 2.79 GJ/t and 0.51 t-CO2-e/t, respectively, representing reductions of 13.35% and 3.77%, respectively, compared with those reported for LC3-50 with 50 % clinker.