【作者】 高迪；

【导师】 彭立敏； Y.L.Mo；

【作者基本信息】 中南大学 ， 土木工程， 2011， 博士

【摘要】 随着现代混凝土工程的大型化、超大型化、工程环境的超复杂化以及混凝土材料应用领域的不断扩大,人们对混凝土材料的要求也逐步提高,高性能混凝土和高功能混凝土是21世纪混凝土材料科学和工程技术发展的重点和方向。而纳米技术在混凝土领域的渗透,打破传统混凝土的局限,极大地扩展了混凝土的应用领域,给混凝土行业带来了崭新的生命力。纳米级碳纤维混凝土作为一种新型建筑材料目前在国际上鲜有研究,国内几乎处于空白阶段。本文以美国国家科学基金项目(NSF项目编号：0634279)为依托,在消化吸收相关文献的基础上,以试验为主、数值分析为辅的研究手段系统地探索了纳米级碳纤维混凝土的基本物理力学性质以及基于电阻变化率的机敏特性等问题。论文的主要研究内容和研究成果如下：(1)在纳米级碳纤维混凝土的制备中,使用三种适合用于混凝土拌制与施工的纳米级碳纤维分散方法,并通过实验结果比较采用不同分散方法制备的纳米级碳纤维混凝土的力学特性和电阻特性。确定了采用聚羧酸盐高效减水剂水溶液作为分散介质,同时配合适量消泡剂对纳米级碳纤维进行分散的方法,可实现纳米级碳纤维对混凝土物理力学性能增强和功能化的目的。(2)通过单轴抗压试验、抗弯试验、劈裂试验和轴向不等辐循环抗压试验对纳米级碳纤维混凝土材料的物理力学性能进行了测试,确定了不同类型纳米级碳纤维在混凝土和自密实混凝土中的最优掺量。电镜扫描结果也表明将适量的分散良好的纳米级碳纤维掺入混凝土中可以增强其抗压强度、劈裂强度,提高混凝土的延性和抗弯性能。(3)从纳米级碳纤维混凝土的电阻特性和导电机理入手,通过试验揭示了纳米级碳纤维混凝土在抗压、抗弯、劈裂和循环荷载试验中电阻变化与应力应变之间的关系。实验结果表明,纳米级碳纤维混凝土试件表现出良好的压敏特性,是一种很有应用前景的具有自监测功能的智能混凝土材料。(4)使用超声波脉冲速度法探讨了普通混凝土和纳米级碳纤维混凝土中脉冲速度与电阻变化率和抗压强度之间关系。试验结果显示出纳米级碳纤维混凝土内部的超声波脉冲速度与其抗压强度具有较好的线性关系,在混凝土应变增大时其内部脉冲速度变化和电阻变化关系也有很好的规律性。因此可利用这些关系来预测混凝土强度,实现对其性质的无损探察。(5)使用基于循环软化模型的有限元程序对纳米级碳纤维混凝土框架剪力墙的抗震性能进行了模拟计算分析。结果表明纳米级碳纤维的加入使得墙体物理力学性能得到提升,其平均延性和抗剪能力也相应增强,因而使用纳米级碳纤维混凝土可以提高剪力墙的抗震性能。(6)通过试验进一步研究了纳米级碳纤维钢筋混凝土梁结构和受弯曲控制的纳米级碳纤维钢筋混凝土桥柱试件的机敏特性。提出纳米级碳纤维钢筋混凝土与纳米级碳纤维素混凝土相似,在工作(受力)状态下荷载或变形与电阻变化率之间存在着相应的关系,进一步验证将纳米级碳纤维混凝土用于结构中而使钢筋混凝土结构智能化的可行性。更多还原

【Abstract】 Concrete is the most widely used construction material and has experienced the developing stages of normal strength concrete, high strength concrete and high performance concrete. Due to the nano size, concrete with nano particles is superior to normal strength concrete because of the special properties of nano-engineered concrete and as a result, the development of Nano technology today greatly diversify the application of traditional concrete. On the other hand, carbon nanofibers (CNFs) have many advantages in both mechanical and electrical properties such as high strength, high Young’s modulus and high conductivity. In this paper, an innovative carbon nanofiber reinforced concrete is proposed by mixing nanofiber into normal concrete to produce nano-engineered concrete. The mechanical properties and strain self-monitoring properties based on variation of electrical resistance (ERV) of the proposed carbon nanofiber reinforced concrete have been studied. Finally, a reasonable concentration of CNF is obtained for use in concrete which not only enhances compressive strength, but also improves the electrical properties required for strain monitoring, damage evaluation and self-health monitoring of concrete and the test results show it is attractive to make smart, high performance concrete using CNFs. The main research contents are as follows:(1) How to dissolve the carbon nanofiber into concrete was studied. The test results indicate that it is feasible to disperse CNFs in Self-Consolidating Concrete (SCC) using the polycarboxylate high range water reducer solution. The enhancement of concrete’s strength and functionality can also be achieved.(2) The optimal concentration of CNFs in concrete has been found by conducting compressive test、four point bending test、split tensile test、cyclic loading with various stress amplitudes test and SEM test. Well-dispersed CNFs in the appropriate concentration allows for the significant mechanical enhancement of concrete such as compressive strength、split tensile strength、flexural strength and ductility.(3) Based on the theoretical analysis of electrical resistance property and electrical conductivity mechanism of CNF-concrete composite, the behavior of composite’s ERV under loading and the correlations between ERV and strain (stress) was experimentally investigated simultaneously by conducting compressive test、four point bending test、split tensile test、cyclic loading with various stress amplitudes test. It was found that the ERV was strain dependent and strain self-monitoring because its electric resistance changes linearily with applied strain, which is named as "piezoresistivity", and consequently, may be used in applications that require strain monitoring and make concrete itself a smart sensor.(4) The pulse velocity method was used to characterize properties of concrete containing CNFs. Concrete strength correlations between pulse velocity, ERV in nondestructive and destructive tests were analyzed for each mix proportions and in each series. These correlations are presented in the form of regression equations. The tests results indicate that the compressive strength, pulse velocity and percent reduction in electrical resistance while loading concrete containing CNF are much greater than those of plain concrete. This regularity may be used for predicting the strength and nondestructive detection of CNF-Concrete composite.(5) The stress-strain curves of concrete containing CNFs are similar to those of plain concrete; therefore, the uniaxial constitutive law of plain concrete in Cyclic Softened Membrane Model (CSMM) is also applicable for concrete containing CNFs. The seismic performance of two framed shear walls was analyzed using cyclic load with the CSMM-based finite element program. Both of the shear force capacity and ductility of shear walls with carbon nanofibers were improved significantly. It shows CNFC can be used to enhance the seismic performance of framed shear walls.(6) Only normal concrete containing CNFs without rebar were investigated in the preliminary research, therefore, the further studies on behavior of ERV of concrete beam with rebar containing CNFs and concrete bridge column with rebar containing CNFs under flexural loading and cyclic laoding are experimentally conducted. It shows similar results to those of plain concrete containing CNFs and verified the feasibility of adding CNFs into concrete structure to make it superior and smart.更多还原