Chemical and mineralogical characteristics of carbonated and uncarbonated cement pastes subjected to high temperatures
Chemical and mineralogical characteristics of carbonated and uncarbonated cement pastes subjected to high temperatures
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DOI：
10.1016/j.compositesb.2021.108861
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发表时间：
2021-04-06
影响因子：
13.1
通讯作者：
Xing, Feng
中科院分区：
文献类型：
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作者：
Li, Yongqiang;Mi, Tangwei;Xing, Feng
碳化混凝土在高温下的耐火性能是显著的，因为它直接暴露在意外火灾中。为了评价碳化对混凝土耐火性能的影响，本研究采用热重分析（TGA）、x射线衍射（XRD）、29Si核磁共振（29Si NMR）等显微测量方法，深入研究了高温作用下未碳化和碳化水泥浆体的化学和矿物学变化。未碳化水泥浆体结果表明，在400 ？C随着石灰的形成，而C?S？H恰好同时生成了硅的单体四面体。720以上？C，所有的C?S？氢解聚成结晶C2S。另一方面，碳化水泥浆显示无定形碳酸钙和部分钙石在400？600年?C，而其余的水晶石和方解石在600？720 ? C。用热重分析曲线无法得到碳酸钙多晶的个别含量。此外，钙改性硅酸盐凝胶在500 ？在950℃时完全解聚成结晶C2S。综上所述，碳化后的膏体具有更好的耐高温性能，其吸热能力是未碳化样品的3.3倍，这延缓了内层的温度发展。因此，合理的碳化工艺可以在一定程度上提高混凝土的耐火性能。
The fire-resistance of carbonated concrete under high temperatures is significant due to its direct exposure during an accidental fire. To evaluate the carbonation effect on fire-resistance of concrete, the chemical and mineralogical changes of uncarbonated and carbonated cement pastes subjected to high temperatures were thoroughly investigated in this research by employing micro-measurement methods including thermal-gravimetric analysis (TGA), X-ray diffraction (XRD) and 29Si nuclear magnetic resonance (29Si NMR). Uncarbonated cement paste results showed the decomposition of portlandite at 400 ?C with the formation of lime, whilst the depolymerization of C?S?H happened simultaneously to generate monomeric silicon tetrahedron. Above 720 ?C, all the C?S?H depolymerized to crystalline C2S. Carbonated cement pastes on the other hand showed that amorphous calcium carbonate and part of vaterite decomposed between the range of 400?600 ?C, while the rest of the vaterite and calcite were decomposed at 600?720 ?C. The individual content of calcium carbonate polymorph could not be obtained using a TGA curve. Besides, the calcium-modified silicate gel was significantly decomposed at 500 ?C and completely depolymerized to crystalline C2S at 950 ?C. In summary, carbonated pastes show better resistance to high temperatures with its heat absorption capacity 3.3 times as high as the uncarbonated sample, which delays the temperature development in the inner layer. Therefore, a reasonable carbonation process could help to improve the fire resistance of concrete to some extent.