【作者】 贾兴文；

【导师】 钱觉时；

【作者基本信息】 重庆大学 ， 材料科学与工程， 2009， 博士

【摘要】 机敏混凝土是具有自感知、自适应和损伤自修复等智能特性的多功能材料,利用这些特性可以实现结构的在线健康监测和损伤检测,在大型土木工程结构和基础设施的健康监测以及电子设备的电磁屏蔽等领域具有广阔的应用前景。目前主要是利用碳纤维、石墨、炭黑、钢纤维等导电材料制作导电机敏混凝土。但是碳纤维价格高昂,在混凝土中分散性较差,表面处理也较为复杂;石墨或炭黑掺量较高时,导电混凝土强度明显下降;钢纤维在混凝土的碱性环境中易钝化,使钢纤维导电混凝土的电阻率随着龄期的增长明显增大。上述问题严重制约了导电机敏混凝土的应用,因此研究导电性、压敏性和力学性能良好、价格低廉且实用价值高的导电机敏混凝土具有非常重要的意义。铁氧化物(Fe_1-δO)包括FeO、Fe₂O₃和Fe₃O₄,都是非化学计量化合物,并且都存在结构缺陷,因此Fe_1-δO具有半导体的性质。FeO和Fe₃O₄在常温下的电阻率分别为5×10^-2Ω·cm和4×10^-3Ω·cm,与沥青基碳纤维的电阻率基本相同。磁选粉煤灰和钢渣中Fe_1-δO的含量约为30%,因此磁选粉煤灰和钢渣有可能作为导电材料用于制备导电砂浆。利用磁选粉煤灰和钢渣,采用制备普通砂浆的工艺制备的废渣砂浆价格非常低廉。通过对比试验发现,当磁选粉煤灰掺量超过40%或钢渣掺量超过50%时,废渣砂浆的导电性与掺加粗细集料的碳纤维混凝土或石墨混凝土的导电性基本相同,而压敏性和力学性能优于上述两种导电混凝土。利用含Fe_1-δO废渣制备出了导电性和压敏性良好、价格低廉且同时具有良好力学性能的导电砂浆,不仅拓宽了机敏混凝土的研究范围,也有利于促进新型智能建筑材料的研究与应用。在分析废渣砂浆的导电性和压敏性机理的基础上,系统地研究了含Fe_1-δO废渣砂浆的导电性和不同荷载条件下废渣砂浆的压敏性,以及含水率、温度、废渣掺量、养护制度等因素对废渣砂浆导电性和压敏性的影响。通过试验发现:（1）随着废渣掺量的增加,废渣砂浆的导电性和压敏性逐渐增大;随着龄期的延长,废渣砂浆的导电性逐渐减弱,压敏性逐渐增大,但28d龄期后导电性和压敏性趋于稳定。（2）随着废渣砂浆导电性的增强和龄期的延长,含水率、温度、养护制度和试件尺寸等因素对废渣砂浆导电性和压敏性的影响逐渐减弱。（3）废渣导电砂浆具有良好的压敏性,荷载作用方式对压敏性有很大影响。（4）随着加荷速度的增加,废渣砂浆的压敏性逐渐增强。（5）三轴受压时,随着围压的增大,在较低应力状态下,废渣砂浆的压敏性有所减弱。（6）废渣砂浆的电阻变化和应力变化具有较好的相关性,在循环荷载作用下,当应力小于弹性极限时,随着应力的循环变化,废渣砂浆的电阻也产生循环变化,但电阻变化滞后于应力变化。通过模拟冻融循环,干湿循环,酸、碱、盐侵蚀和碳化等侵蚀性环境,研究了废渣砂浆在侵蚀性环境中导电性和压敏性的变化,以及导电性和压敏性变化与力学性能变化的关系。经历多次冻融循环、酸溶液以及硫酸盐侵蚀,废渣砂浆的导电性和压敏性明显降低;经历多次干湿循环,废渣砂浆导电性和压敏性逐渐降低;NaCl溶液和碱溶液浸泡后,废渣砂浆的导电性和压敏性明显增强;人工碳化对废渣砂浆的导电性和压敏性没有明显影响。在侵蚀性环境中,废渣砂浆的力学性能变化与导电性变化明显相关,通过监测废渣砂浆的电阻变化,可以反映其力学性能的变化。这也说明通过监测混凝土材料在侵蚀性环境中的电阻变化,可以为评估其耐久性和损伤提供参考。更多还原

【Abstract】 Smart concrete has self-diagnosis, adaptive function, and damage self-repairing, so it can be used to monitor structure health and detect injury. Carbon fiber, graphite, carbon black, and steel fiber can be used to make smart concrete. But carbon fiber is high in price, low in dispersion and complicate in surface treatment. With the increasing of graphite and carbon black content, the compressive strength of conductive concrete decreases markedly. Steel fibers are easy to be oxidized, so the electrical resistivity of steel fiber reinforced concrete increase with age. The above problems hamper the application of conductive concrete. So it is very important to study the conductive smart concrete which has electrical conductivity, compressive sensitivity, and good mechanical properties.Fe_1-δO includes FeO, Fe₂O₃ and Fe₃O₄, all of which are nonstoichiometric compounds and have structure defect, so Fe_1-δO have the properties of semiconductor. The electrical resistivity of FeO and Fe₃O₄ are 5×10^-2Ω·cm and 4×10^-3Ω·cm respectively, which are basically the same as that of pitch-based carbon fiber. The content of Fe_1-δO is over 30% in the magnetic fly ash and steel slag, so the above-mentioned two kinds of waste may be used as conductive materials to make electrical conductive mortar. Using the magnetic fly ash and steel slag as the conductive materials, the price of the waste mortar, which is made by the technique in making normal mortar, is very low. When the waste content is beyond the percolation threshold, they have good conductivity, compression sensitivity and excellent mechanical properties. With the increasing of waste content, its electrical resistivity is close to that of CFRC and graphite concrete to which the coarse aggregate is added; while its compression sensitivity is better than the above two types of concrete.Fe_1-δO waste conductive mortar is a smart material. The author analyzes the mechanism of conductive and compression sensitivity. On the basis of the study of electrical conductivity and smart properties, the author first studies its conductive properties and smart properties under different loading conditions, and then studies some factors that influence the electrical conductivity and smart properties, including the water content, temperature, content of waste, curing regime. Main results are as follows:①The electrical conductivity and compressive sensitivity of conductive mortar increase with the increasing of waste content. With the age increasing, the electrical conductivity decreases and the compressive sensitivity increases.②With the increasing of electrical conductivity and age, the influences of water content, temperature, curing regime and specimen size are weakening gradually.③The loading modes have great influence on the compression sensitivity of conductive mortar. Under the pressure, conductive mortars have good compression sensitivity.④Under the uniaxial loading, with the increasing of loading rate, the compression sensitivity increases.⑤Under the triaxial loading, with the increasing of confining pressure, when under relatively low stress, the compression sensitivity weakens⑥Under the recycling loading, when the maximum stress is within the elastic limit, the resistivity of mortar changes periodically with the stress changing, but the change of resistivity lags behind that of the stress.On the basis of the above examination, the author studies the erosion environment condition which influences the electrical conductivity and smart properties of mortar, including freeze-thaw cycle, dry-wet cycle, acid, alkali, salt and carbonation. At the same time, the author studies the relationship of electrical conductivity and smart properties changing with the mechanical properties.Freeze-thaw, acid and sulfate have remarkable adverse influences on the electrical conductivity, compressive sensitivity, and mechanical properties. After dry-wet cycles, the electrical conductivity and compressive sensitivity decrease slowly. After long-term immersion into alkali solution and salt solution, the electrical conductivity and compressive sensitivity increase remarkably. Carbonation has no effect on the electrical conductivity or compressive sensitivity. The change in electrical conductivity is remarkably related to the mechanical properties. Therefore by monitoring the resistivity change of waste mortar can reflect the change of mechanical properties. That indicates monitoring the resistivity change of cement-based materials can provide reference for evaluating the durability and injury of cement-based materials.更多还原