Choi Heesup, Inoue Masumi, Kim Dongmin, Choi Hyeonggil, Sengoku Risa
Department of Civil and Environmental Engineering, Kitami Institute of Technology, Hokkaido 090-8507, Japan.
Department of Infrastructure Safety Research, Korea Institute of Civil Engineering & Building Technology, Gyeonggido 10223, Korea.
Materials (Basel). 2019 Aug 1;12(15):2456. doi: 10.3390/ma12152456.
Concrete has a remarkably low ratio of tensile strength to compressive strength, and is widely used in construction. However, the occurrence of cracks in a concrete structure is inevitable. Nevertheless, in the presence of adequate moisture, small cracks in the concrete structure exhibit a propensity to self-heal by getting filled due to the rehydration of cement particles and the subsequent precipitation of calcium carbonate (CaCO). According to previous studies, the self-healing performance can be maximized by optimizing the temperature and pH to control the crystal formation of CaCO. This study focused on the crystal form of CaCO generated in the self-healing of a cement-based composite material. To evaluate the self-healing performance depending on the type of aqueous solution and the temperature, the weight change, the weight change rate, and the porosity reduction in each case were evaluated. Moreover, to increase the generation of CaCO (which is a self-healing precipitate), nanosized ultrafine CO bubbles using CO gas were used, along with an adequate supply of Ca by adjusting the aqueous solution (Ca(OH), CaO + ethanol). For greater pore-filling effects by controlling the CaCO crystal forms in the cement matrix, the change in the crystal form of the precipitated CaCO in the hardened cement paste with changing temperature was analyzed by scanning electron microscopy and X-ray diffraction. As a result, the possibility of the effective generation and control of vaterite with a dense pore structure together with calcite was confirmed by adjusting the temperature to approximately 40 °C at a pH of 12.
混凝土的抗拉强度与抗压强度之比极低，因此在建筑中被广泛使用。然而，混凝土结构中出现裂缝是不可避免的。不过，在有足够水分的情况下，混凝土结构中的小裂缝由于水泥颗粒的再水化以及随后碳酸钙（CaCO₃）的沉淀而有自行愈合的倾向，即裂缝会被填满。根据以往的研究，通过优化温度和pH值来控制碳酸钙的晶体形成，可以使自愈性能最大化。本研究聚焦于水泥基复合材料自愈过程中生成的碳酸钙的晶体形态。为了评估取决于水溶液类型和温度的自愈性能，对每种情况下的重量变化、重量变化率和孔隙率降低情况进行了评估。此外，为了增加作为自愈沉淀物的碳酸钙的生成量，使用了利用CO₂气体产生的纳米级超细CO₂气泡，并通过调整水溶液（Ca(OH)₂、CaO + 乙醇）来充分供应Ca。为了通过控制水泥基体中碳酸钙的晶体形态获得更大的孔隙填充效果，利用扫描电子显微镜和X射线衍射分析了硬化水泥浆体中随着温度变化沉淀的碳酸钙晶体形态的变化。结果表明，在pH值为12时将温度调节至约40℃，证实了有可能有效地生成和控制具有致密孔隙结构的球霰石以及方解石。
