掺CaCO3粉及后续水养护对CO2养护混凝土强度和显微结构的影响

Effects of CaCO_3 Powder and Subsequent Water Curing on Compressive Strength and Microstructure of CO_2-cured Concrete

研究了掺CaCO_3粉及后续水养护对CO_2养护混凝土的强度的影响。采用X射线衍射和热重方法分析了两者对CO_2养护后反应产物的影响,同时采用扫描电子显微镜观察了掺CaCO_3粉及后续水养护对混凝土微观结构的影响,并用能谱仪对微区元素进行了表征。结果表明:当剩余水灰比为0.18时,掺10%CaCO_3粉混凝土CO_2养护及后续水养护后的抗压强度均达到最大值。与未掺时相比,掺10%CaCO_3粉可提高混凝土CO_2养护及后续水养护7 d的抗压强度,但后续水养护28 d的抗压强度略有降低。由于CO2养护后还存在未与CO2反应的水泥颗粒,后续水养护可进一步提高CO_2养护混凝土的强度,反应生成的碳酸钙的结晶程度也有所提高。在后续水养护过程中,CaCO_3粉作为晶核促进钙矾石的散射状生长。

The effects of CaCO3 powder and subsequent water curing on the compressive strength of CO2-cured concrete were investigated. The reaction products of concrete after CO2 curing were determined by X-ray diffraction and thermogravimetry- differential thermogravimetry, and the microstructure changes of concrete after incorporating CaCO3 powder and/or after subsequent water curing were characterized by scanning electron microscopy affiliated with energy dispersive X-ray spectroscopy. The results show that when the residual water-cement ratio is 0.18, the compressive strength of concrete after CO2 curing and subsequent water curing reaches the maximum value. Compared to the concrete without CaCO3 powder, incorporating 10% CaCO3 powder increases the compressive strength of concretes after both CO： curing and 7 d subsequent water curing, but slightly decreases the compressive strength of concrete after 28 d subsequent water curing. During the subsequent water curing, the strength of the CO2-cured concretes increases continuously with time due to the CO2-cured concrete with some unreacted cement. The crystallization degree of the produced carbonates also increases. In addition, the CaCO3 powder, as crystal nucleus, promotes the formation of ettringite.