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

波特兰水泥的生产是一个能源密集型过程。其高的早期强度依赖于在1500℃下形成的高比例的硅酸三钙(C3S)。硅酸氢钙(C2S)基贝利特水泥可节约能源20%，具有较好的长期使用性能。贝利特水泥的主要问题是，即使有掺杂剂，C2S的水化速度也比C3S慢得多。另一方面，所有的C2S多晶型都可以被二氧化碳激活，以产生与C3S相同的高早期强度。C2S的独特特性暗示了一种使用贝利特水泥的创新方式：二氧化碳活化以获得早期强度，随后的水化以获得长期性能。本研究旨在开发出符合节能降耗和快速早强要求的贝利特特种水泥。由于早期强度取决于碳化作用，而不是水化作用，因此富钙和富硅的工业废料可以作为贝利特水泥的唯一原材料。二氧化碳的活化是一个碳吸收过程。如果CO2活化硬化能够封存合成过程中因使用燃料而回收的二氧化碳，则生产有可能达到零排放状态。这样生产的混凝土将具有更好的抗大气碳化、离子渗透、硫酸盐侵蚀和冻融循环的能力。研究将研究高温和水热合成工艺，以利用两种工业废弃物：钢铁生产的钢包渣和火力发电厂的飞灰来生产贝利特水泥。贝利特熟料将通过物相分析进行表征，其水泥将进行碳化和水化反应检测。贝利特混凝土将接受强度、耐久性和固碳能力测试。为了加深对CO2活化贝利特水泥碳化键机理的认识，促进其工业化应用，将对碳化诱导的微观结构进行全面的微观分析。由于CO2活化可加速养护，该系统最适合预制混凝土产品，如砌块、面板、管道和楼板。独特的固井系统是同类产品中的第一个，提供了巨大的好处。

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.