硬化水泥净浆的太赫兹介电常数和其孔结构的GEM模型分析

Characterization of Terahertz Dielectric Constant and Pore Structure of Hardened Cement Paste with GEM Model

【目的】深入了解水泥净浆的孔结构对于研究如何提升水泥基材料的性能是非常必要的。【方法】使用太赫兹时域光谱(THz-TDS)技术测试得到水灰比为0.3,0.4,0.5,水化龄期为7 d、28 d、56 d的干燥硬化水泥净浆在0.2~2 THz频段的时域信号。利用时域信号下的延迟时间计算得到水泥净浆的折射率和介电常数。【结果】结果显示,同一龄期下水泥净浆的介电常数随水灰比增大而减小;相同水灰比水泥净浆的介电常数则随龄期变化不明显。使用General Effective Media(GEM)模型建立了水泥净浆有效介电常数和其孔结构之间的关系,通过实验数据拟合,得到水泥净浆中水化产物固体相的介电常数为8.73.【结论】通过对GEM模型进行参数分析发现,水泥净浆的孔隙率是影响其有效介电常数最主要的因素。

【Purposes】A deep understanding of the pore structure of cement paste is important for improving the performance of cement-based materials.【Methods】In this paper,terahertz time-domain spectroscopy(THz-TDS)system was used to test the terahertz time-domain signal of dry cement paste with water cement ratio of 0.3,0.4,0.5 and hydration ages of 7,28 and 56 d in the frequency range of 0.2~2 THz.The refractive index and dielectric constant of cement paste were calculated by using the delay time of time-domain signal.【Findings】The test results show that the dielectric constant of cement paste decreases with the increase of water-cement ratio at the same age.The dielectric constant of cement paste with the same water cement ratio does not change obviously with age.The relationship between the effective dielectric constant and pore structure of cement paste is established by using the General Effective Media(GEM)model.Through the fitting of experimental data,the dielectric constant of the solid phase of hydration products in cement paste is 8.73.【Conclusions】According to the GEM model parameter analy-sis,the porosity of cement paste is the most important factor affecting its effective dielectric con-stant.