Synthesis of Hydraulically Active Calcium Silicates Produced by Combustion Methods

ABSTRACTPortland cement is synthesized from a mixture of limestone and clay at high temperature (1450 °C) via a conventional process (solid-phase synthesis), in which partial fusion of raw materials and the formation of clinker nodules are produced. The clinker is mixed with a small percentage of gypsum and ground together to make the cement. This synthesis process holds the cement industry accountable for 5–8% of global anthropogenic CO2 emissions. The production of a ton of cement emits between 0.62 and 0.97 tons of CO2 into the atmosphere, depending on the processing plant. Furthermore, the use of fossil fuels in cement production is another important factor in the environmental impact of this industry. The production of 1 ton of clinker consumes approximately 5.86 GJ per tons of clinker produced in wet processes and 3.35 GJ per tons of clinker produced by dry process. Some researches have reported the possibility to obtain silicate and aluminate cements by alternative synthesis methods, which optimize both time and temperature, such as Pechini method, sol-gel method and microwave assisted method. The combustion methods, another alternative, are chemical redox processes in which the use of chemical precursors and organic fuels at high temperature generate a self-sustaining fastwave. The said wave is characterized by the fact that once the initial exothermic reaction starts, it generates a reaction wave (0.1–10 cm/s) at high temperature (1000–3000 °C) that propagates, in a self-sustaining way, through the heterogeneous mixture which leads to the formation of the solid material. For this reason, and the irreplaceable role of cement in the construction industry, this paper shows the advances in the production of silicates, similar to those found in the Portland cement, by combustion synthesis method.This paper shows the production of calcium silicates similar to the silicates of Portland cement, by combustion synthesis. Thermal analysis and XRD techniques were used to compare the syhthetized silicates with alite and belite of Portland cement.