智能同轴钢筋混凝土构件的相关介电理论和传输反射特性研究

One kind of smart coaxial one-dimensional reinforced concrete member is proposed by putting a longitudinal reinforcing bar as the inner conductor in the center of the member, regarding the reinforcing bar cage of the member as the outer conductor and the concrete as dielectric, based on the structural principle of coaxial cable. Both of the mechanical properties and the functional properties of one kind of material will be utilized in this kind of member. Life cycle structure health monitoring on reinforced concrete structures by this technique may come true. .According to the theory of electromagnetic wave transmission in the concrete and the dielectric behavior of concrete, the complex permittivity spectroscopy of concrete with different damage levels or different crack states are measured to probe the correlation between dielectric properties and damage state of concrete, and also to build a dielectric constant model, in which the damage state of concrete and the ratio of water: cement: sand: aggregate will be considered. Meanwhile, the microstructure and damage evolution of concrete will be also taken into account to interpret how the interfacial polarization changes at different crack states. Furthermore, damage characteristic frequency domain for permittivity of concrete will be investigated based on notable interfacial polarization and dielectric relaxation occurring during inner concrete damage or crack. .Proper size elements of smart coaxial one-dimensional reinforced concrete with different damage or crack state will be chosen to measure their scattering parameters. .The complex permittivity of concrete in the smart coaxial one-dimensional reinforced concrete member and element will be measured according to the detection principle of coaxial cable. Finite element method will be employed to build the lumped parameter model for the smart coaxial one-dimensional reinforced concrete member. Damage identification method or crack detection method will be proposed based on complex permittivity of concrete or scattering parameter of element. The reflected signal will be identified by using time-frequency domain analysis method. Discontinuous location of dielectric constant in concrete will be found according the time interval between the incident signal and the reflected signal. .This research is to explore a novel way for structure health monitoring, and try to resolve some fundamental theoretical problem. It is expected to provide a new idea for building smart city and resilience city.

借鉴同轴电缆的原理，在一维钢筋混凝土构件中纵向放置钢筋作为内导体，视构件自身的钢筋笼作为外导体，视构件自身的混凝土为介电质，设计出一种智能同轴一维钢筋混凝土构件，以实现材料的结构性和功能性一体化和结构健康检测的全寿命期化。.利用电磁波在混凝土介质中传输理论和混凝土介质的介电性质，结合混凝土材料的微观组构特征和损伤演化理论，采用试验方法测试不同损伤混凝土的介电谱特性，深入研究混凝土内部损伤演化与其呈现的介电特性之间的关系，形成能描述混凝土损伤程度的介电模型；探究对内部损伤表现出显著界面极化或介电弛豫规律的介电损伤特征频率。.根据同轴电缆的检测原理，测试智能同轴一维钢筋混凝土构件中混凝土的介电常数，用有限元法建立构件的集总参数模型，建立基于介电常数或散射参数的损伤判断方法。利用时频域分析法识别反射信号，根据介电常数的不连续位置来探伤。.研究成果对探索智慧城市和韧性城市建设提供新的思路。

借鉴同轴电缆的原理，在一维钢筋混凝土构件中植入钢筋作为内导体，将构件自身的钢筋笼作为外导体，视构件自身的混凝土为介电质，设计了一种智能同轴一维钢筋混凝土构件，利用电磁波在混凝土介质中的传输特性，探索了混凝土介质的介电性质与混凝土材料的微观组构特征之间的本征关系，以实现材料的结构性和功能性一体化，为智慧城市和韧性城市建设提供新的探索性思路。.研发了同轴钢筋混凝土构件电磁参数测试系统、水泥基材料介电参数平板电容法测试装置、水泥基材料矩形波导法测试装置、水泥基材料电磁参数同轴探头法测试系统，并基于电磁学相关理论，建立测试参数与电磁参数之间转换模型。在研究影响水泥基材料微细观结构关键因素的基础上，提出了以水胶比、砂胶比、龄期、养护制度、预设裂缝以及受力大小为变量的研究方案，系统研究了各变量的变化对水泥基材料介电参数的影响规律，并初步揭示了材料内部界面极化机理。试验验证了同轴钢筋混凝土构件混凝土内部缺陷自检的可行性，建立了损伤同轴钢筋水泥净浆构件的等效电路简化模型及相应的电参数表达式，揭示了钢筋混凝土构件弯剪破坏过程中的阻抗、相位等电学参数的变化规律。.本项目采用了四种测试手段均表明，水泥基材料的介电参数与影响其内部结构致密程度或内部空隙分布情况的水灰比、砂灰比、龄期、养护制度、预设裂缝等因素密切相关，水泥基材料的内部损伤演化与其所呈现的介电特性存在相对稳定的映射关系，即材料的力学特性有望通过电学参数来表征。水泥基材料的介电参数受测试频率的影响较大，测试装置的几何尺寸、材料属性、待测试块的几何尺寸和外形等因素亦会影响介电参数的测试结果。研究表明，同轴探头法测试水泥基材料介电常数的特征频率宜取2.5GHz；基于理论分析和仿真模拟结果对同轴探头的几何尺寸和材质、待测水泥基的尺寸和观要求给出了建议。.研究成果有望开辟一种全新检测方法，对确保钢筋混凝土结构全寿命安全具有重要意义。