CO2-activated belite cements synthesized from industry wastes and the carbonation bond mechanism

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Production of Portland cement is an energy intensive process. Its high early strength is dependent on high percentage of tricalcium silicate (C3S) which is formed at a temperature of 1500 oC. Dicalcium silicate (C2S) based belite cement can be made with 20% less energy and can have a better long term performance. The main problem with belite cement is that C2S hydrates much more slowly than C3S even with dopants. On the other hand, all C2S polymorphs can be activated by carbon dioxide to produce equivalent high early strength as C3S. The unique characteristic of C2S suggests an innovative way of using belite cement: carbon dioxide activation for early strength and subsequent hydration for long term performance. This proposed research is to develop special belite cements in line with the attempt to reduce energy consumption and produce fast early strength. Since early strength is dependent on carbonation, rather on hydration, calcium-rich and silica-rich industry wastes can be utilized as exclusive raw materials for belite cement. CO2 activation is a carbon uptake process. If CO2 activated hardening can sequester carbon dioxide recovered from synthesis process due to the use of fuel, the production is possible to reach a state of zero-emission. The concrete so produced will have more resistance to atmospheric carbonation, ion penetration, sulphate attack and freeze-thaw cycling. Research will investigate both high temperature and hydrothermal synthetic processes to manufacture belite cement with two industry wastes: ladle slag from steel production and fly ash from thermal power plant. Belite clinkers will be characterized by phase analysis and their cements will be examined for carbonation and hydration reactions. Belite concrete will be tested for its strength, durability and carbon sequestration capacity. To enhance the understanding of the carbonation bond mechanism in CO2 activated belite cement and promote commercial applications, a comprehensive microanalysis of carbonation induced microstructure will be performed. Because of the accelerated curing by CO2 activation, the system is best suited to precast concrete products such as blocks, panels, pipes and slabs. The unique cementing system, first of its kind, offers tremendous benefits.