【作者】 杨楠；

【导师】 孙全胜；

【作者基本信息】 东北林业大学 ， 道路与铁道工程， 2020， 博士

【摘要】 本文以聚氨酯水泥(PUC)加固桥梁的工程实践为背景,通过向PUC中加入纳米碳纤维(CNF)等导电填料,将其制成纳米碳纤维聚氨酯水泥(CPUC)复合材料。从CPUC的制备、力学特性入手,对CPUC的机敏特性进行了系统研究,并提出了一种简便易行的评估CNF分散效果的方法。研究了 CPUC在疲劳荷载作用下的电阻率变化规律,利用CPUC电阻率变化对其疲劳累积损伤进行定量评定。通过CPUC材料加固混凝土大梁,建立电阻变化率与外荷载关系模型,对梁体的承载力状况进行实时评估,加固的同时实现了梁体健康监测的双重效果。利用CPUC加固混凝土柱,提高柱承载能力的同时,通过CPUC的纵向电阻变化率预估钢筋纵向应变,对柱体损伤程度进行定量表征,形成具有损伤自诊断功能的外包CPUC混凝土柱体。最后,以某加固实桥为例,利用集成型CPUC智能传感器,对主梁张拉体外预应力钢束前后,及静载试验下的主梁关键截面应变进行监测,验证了其在工程应用中的可行性。本研究为CPUC在智能监测方向的工程应用提供了理论依据与方向。主要研究成果如下:1、以双组分聚氨酯(PU)为胶凝材料,水泥作为主要细集料,CNF作为主要导电填料,通过对CNF粒子进行表面化学改性,采用机械高速共混的一步法制备CPUC复合材料。CPUC的平均抗压、抗弯强度分别为53.7 MPa、30.75 MPa;当温度介于-40℃～40℃时,直接拉伸强度范围在24.13MPa与18.13MPa之间,极限应变小于5500με;CPUC与混凝土之间的粘结应力平均值为3.47MPa,大于混凝土材料自身的粘结强度;粘结抗剪强度可达3.08MPa,与未掺加碳纤维的PUC相比,粘结抗剪强度提高了8%。2、以灵敏度500作为压敏特性的参考指标,建立CPUC复合材料CNFs导电填料浓度与其相应正六面体电阻变异系数二次曲线关系,可评估CPUC复合材料中CNFs的分散效果,进而判别CPUC的灵敏度特性,为CPUC拌合物灵敏度的判别提供一种简便易行的新方法。3、疲劳荷载作用下,CPUC疲劳寿命符合两参数的weibull分布,CPUC弯拉状态下电阻率随着疲劳应力幅值与循环次数的增加而增加,呈现三阶段的变化规律;不同环境温度疲劳荷载作用下,CPUC弯拉电阻率随温度的增加而逐渐增大,可利用CPUC电阻率变化预测其弯拉疲劳累积损伤,采用损伤阈值电阻率,或极限电阻率作为开始损伤或破坏的衡量标准,为实际工程应用提供理论基础。4、利用CPUC材料加固混凝土大梁,可显著提升梁的屈服荷载与极限荷载,作为加固材料时CPUC与PUC相比,对梁体极限荷载、延性指数提升较大。CPUC弯曲过程中的电阻变化率可反映钢筋受力过程中应变状态的全过程,可利用CPUC电阻变化率的突变监测钢筋屈服,进而对构件进行安全预警,借助CPUC材料初始电阻变化率-拉应变的本构关系,建立电阻变化率与外荷载关系模型,可对梁体的承载力状况进行实时评估,加固的同时实现了梁体健康监测的双重效果。5、利用CPUC加固混凝土柱,可使柱承载能力、延性与能量耗散能力得到不同程度的提高,且随CF掺量的增加提升较为显著。可利用CPUC的纵向电阻变化率预估钢筋或混凝土的纵向应变,对柱体损伤程度进行定量表征,形成具有损伤自诊断功能的外包CPUC混凝土柱体,为结构的健康监测、预警提供了新途径。6、利用集成型CPUC智能传感器,对某实桥箱梁张拉体外预应力钢束前后,及加固后静载试验主梁关键截面的应变进行测量,表明CPUC智能传感器可对混凝土表面应变进行实时监测,进而对构件的损伤程度进行定量评估,并具有一定的安全储备,验证了其在工程应用中的可行性、可靠性。更多还原

【Abstract】 This paper takes the engineering practice of polyurethane cement(PUC)to reinforce bridges as the background.By adding conductive fillers such as nano-carbon fiber(CNF)to the PUC,it is made into nano-carbon fiber polyurethane cement(CPUC)composites.According to the preparation and mechanical properties of the CPUC,a systematic study on the sensitivity characteristics of CPUC is carried out,and a simple and easy method is proposed to evaluate the CNF dispersion effect.The variation regulation of CPUC resistivity under fatigue load is studied,and the fatigue cumulative damage is quantitatively evaluated by CPUC resistivity change.At the same time,the relationship model between resistance change rate and external load is established,and the bearing capacity condition of beam body is evaluated in real time.Moreover,the double effect of beam body health monitoring is realized.While strengthening the concrete column by CPUC to improve the bearing capacity of the column,the longitudinal strain of the steel bar is evaluated by the change rate of the longitudinal resistance in the CPUC,and the damage degree of the column is quantitatively characterized to form an outer CPUC concrete column with the function of self-diagnosis of damage.Finally,a reinforced solid bridge is used as an example to monitor the strain of the key section of the main beam before and after tensioning the prestressed steel bundle outside the main beam and under the static load test by using the integrated CPUC intelligent sensor,which verifies its feasibility in engineering application.And this research provides theoretical basis and direction for CPUC engineering application in the direction of intelligent monitoring.The main findings are as follows:1.Using two-component polyurethane(PU)as cementitious material,cement as the main fine aggregate and CNF as the main conductive filler,CPUC composites were prepared by one-step method of mechanical high-speed blending by surface chemical modification of CNF particles.The average compressive strength and flexural strength of CPUC are 53.7 MPa and 30.75 respectively MPa.When the temperature is between-40℃～40℃,the direct tensile strength range is between 24.13MPa and 18.13MPa,the ultimate strain is less than 5500 με,and the average value of the bond stress between CPUC and concrete is 3.47MPa,which is greater than the bond strength of concrete material itself.The bond shear strength could reach 3.08MPa,which is 8%higher than that of PUC without carbon fiber.2.Using sensitivity 500 as the reference index of pressure-sensitive characteristics,the relationship between the concentration CNFs conductive filler of CPUC composites and its corresponding positive hexahedron resistance variation coefficient is established,which can evaluate the dispersion effect of CNFs in the composites,and then distinguish the sensitivity characteristics of the CPUC,and provide a simple and feasible new method for the sensitivity discrimination of CPUC mixtures.3.Under fatigue load,CPUC fatigue life accords with the weibull distribution of two parameters,and the resistivity increases with the raise of fatigue stress amplitude and cycle times CPUC bending-pull state.Under different ambient temperature fatigue load,the bending-pull resistivity increases gradually with the increase of temperature.CPUC resistivity change can be used to predict the cumulative damage of flexural and tensile fatigue.The threshold resistivity or ultimate resistivity could be used as the measure of initial damage or failure,which may provide theoretical basis for practical engineering application.4.The yield load and ultimate load of the beam can be significantly increased by using CPUC material to reinforce the concrete beam When as the reinforcement material,CPUC the ultimate load and ductility index of the beam are increased greatly compared with the PUC.The change rate of resistance in CPUC bending process can reflect the whole procedure of strain state in the process of steel bar stress,and the sudden change rate of CPUC resistance can be used to monitor the yield of steel bar,and then safety warning can be carried out.According to the constitutive relation between the initial resistance change rate and the tensile strain of the CPUC material,a model of the relationship between the resistance change rate and the external load can be established to evaluate the bearing capacity of the beam body in real time,and the double effect of health monitoring of the beam body can be realized while strengthening.5.Reinforcement of concrete columns by CPUC can improve the bearing capacity,ductility and energy dissipation capacity of columns to varying degrees,and raise significantly with the increase of CF content The longitudinal strain of steel bar or concrete can be estimated by the CPUC longitudinal resistance change rate,and the damage degree of the column can be quantitatively characterized to form an outer CPUC concrete column with the function of self-diagnosis of damage,which provides a new way for the health monitoring and early warning of the structure.6.Using integrated CPUC intelligent sensor,the strain of the key section of the main beam in static load test before and after tension of a real bridge box girder is measured,which indicates that the CPUC intelligent sensor can monitor the concrete surface strain in real time,then quantitatively evaluate the damage degree of the components,and have a certain safety reserve,which verifies its feasibility and reliability in engineering application.更多还原