基于CF/CNT-CC传感元件的大体积混凝土温度、应力实时监测方法

Monitoring the temperature and stress in mass concrete is one important aspect in the structure health diagnosis. Based on the temperature- sensitive effect and stress- sensitive effect of carbon fiber and carbon nanotube reinfroced cement- based composite(CF/CNT-CC), this project embedded the CF/CNT-CC samples in the concrete as the sensing elements. Then by monitoring the real- time change of resistivity of CF/CNT-CC, the real- time monitoring of the temperature and stress in concrete could be realized. CF/CNT-CC was manufactured by selecting the carbon fibers and carbon nanotubes with proper aspect ratio and electric properties. The influencing factors of resistivity stability and conductive mechanism were studied. Considering the electric properties of CF/CNT-CC, the material design method was proposed to help to solve the temperature/stress coupled problem. The temperature- sensitive and stress- sensitive effect of CF/CNT-CC were studied with deferent material composites to find the changing rule of temperature- resistivity and stress- resistivity. Then the sensitive and stable sensing elements were made and embedded in mass concrete for monitoring tempereature and stress. CF/CNT-CC had very good compatibility with concrete. It could not only monitor the temperature but also monitor the stress. Thus a new method of monitoring the temperature and stress in mass concrete was obtained.

大体积混凝土内部温度及应力监测，是结构安全健康诊断的重要方面。本项目基于碳纤维/碳纳米管-水泥基复合材料(CF/CNT-CC)的温敏、力敏效应，将CF/CNT-CC材料制备成传感元件埋置于混凝土中，通过监测CF/CNT-CC材料电阻率实时变化，实现对混凝土内部温度及应力的实时监测。本项目从材料组成入手，选择合适长径比和电性能的碳纤维及碳纳米管，制备得到CF/CNT-CC材料，并研究其电阻率稳定性的影响因素及导电机理，提出面向CF/CNT-CC材料电性能的材料设计方法，解决温度和应力的耦合问题；分别对不同材料配比的CF/CNT-CC材料进行温敏、力敏效应研究，建立其温度-电阻率、应力-电阻率变化规律，制备灵敏、稳定的温度及应力传感元件，将之用于大体积混凝土内部温度及应力监测。CF/CNT-CC材料与混凝土相容性好，既可监测温度又可监测应力，开辟了大体积混凝土温度、应力监测新方法。

将导电填料掺入到水泥基材料中赋予水泥材料导电性，可制备具有智能特性的水泥基传感器，置入大体积混凝土中，将混凝土内部的应力、温度和湿度等参数转化为电信号输出，以达到实时观测混凝土内部环境的目的。碳纳米管(CNTs)和碳纤维(CFs)具有优异的导电性能，将其掺入到水泥基材料中可获得较好的机敏性能。研究将CFs和CNTs复合掺入到水泥基材料中，利用两种导电材料多尺度协同效应，改善水泥基材料内部导电网络的形成，分析单掺CFs以及复掺CFs和CNTs水泥基材料的微观结构，探究CNTs的掺入对导电网络形成的贡献。在导电性和机敏性能测试中，采用四电极法观测试件电阻率变化，通过电化学阻抗谱分析试件内在导电机理。试验结果证明，与单掺CFs相比，CNTs掺入改善了水泥基材料内部导电网络，除了CFs之间的接触导电和隧道导电之外，还包括CFs与CNTs之间的隧道导电，也使得CF-CNT/CC导电性能优于CF/CC的导电性能。在相同因素影响下，CNT-CF/CC的灵敏度远高于CF/CC。CNT-CF/CC和CF/CC在荷载、温度和湿度影响下的电阻率变化规律相似，但CNT-CF/CC在循环荷载和循环温度作用下的电阻率变化呈现较好的循环可逆性，循环曲线更为规律。掺量为0.3 wt.%CNT-0.4wt.%CF/CC表现出较为优异的力敏、温敏和湿敏性能。将水泥基传感器埋入大体积混凝土中，发现由CNT-CF/CC制作的传感器表现出较好的循环往复性，可用来监测混凝土内部温度及应力变化，为制备高精度、多维度的水泥基复合材料传感器，为实现实际混凝土工程健康检测打下良好的理论基础。