既有隧道结构混凝土材料性能研究

混凝土材料性能劣化是当前隧道结构维护中面临的主要问题,从既有隧道结构维护的角度出发,总结归纳了混凝土碳化和氯离子侵蚀这两种能够影响混凝土材料性能的关键因素的作用机理,并依据工程实践过程,给出了既有隧道结构中混凝土材料性能的鉴定方法.     

智能混凝土与结构

智能混凝土是通过将极少量具有某种特殊功能的材料复合于传统的混凝土材料中形成的具有多功能特性或某一种特殊功能特性的新型土木工程结构材料。与其他智能材料相比,智能混凝土是多功能本征性智能材料,可从本质上提高工程结构的性能。自感知混凝土(纳米混凝土、碳纤维混凝土)、自阻尼混凝土和自愈合混凝土等是智能混凝土研究的热点。总结了近年来作者在智能混凝土的制备、性能、机理,以及智能混凝土结构等方面的研究成果,并指出需进一步研究的问题。     

土木工程结构智能感知材料、传感器与健康监测系统

随着智能感知材料的发展,高性能传感器及其测试技术为结构智能健康监测系统的研究与发展提供了崭新的途径,结构智能健康监测已经成为诸多领域的前沿研究方向.本文重点介绍了作者近年来基于智能感知材料发展的智能传感器及土木工程结构智能健康监测系统的研究成果.主要包括光纤光栅应变和温度传感器与压电薄膜(PVDF)应变和裂缝监测传感器及其性能;无线传感器网络与无线传输技术及其性能与工程应用;碳纤维智能传感器与纤维增强-光纤光栅应变传感器及其性能;智能混凝土与智能混凝土标准应变传感器及其性能;智能健康监测系统及其工程应用.最后,介绍了我国在重大工程结构智能健康监测领域的立项情况.     

水泥基材料微结构演变及其传输性能的数值模拟

水泥基材料劣化的本质是由于侵蚀性介质通过传输通道进入材料内部生成腐蚀物质,从而对结构造成破坏.因此,结构耐久性与侵蚀介质在水泥基材料中的传输行为密切相关.已有的混凝土寿命预测模型和耐久性评估研究主要基于Fick和Darcy定律,本文从水泥基材料微结构出发,结合最新的国内外研究成果,对孔结构演变及其传输性能的数值模拟研究进展进行阐述,对促进结构耐久性的研究具有一定的指导意义.     

应力自感知水泥基复合材料及其传感器的研究进展

应力自感知水泥基复合材料是在传统的水泥或砂浆中添加特定导电材料或纳米材料复合而成的具有压阻效应的材料。利用这类材料的电阻率与其自身压应力存在一定对应关系的特性, 可以制成性能独特的应力自感知水泥基复合材料传感器。此类传感器因具有造价低、耐久性好、埋设工艺简单以及与混凝土材料相容性好等特性, 有望成为混凝土结构长期健康监测的新一代传感装置。本文作者从原材料选择、搅拌工艺、电阻测试方法以及传感器测试系统等多方面综合评述了应力自感知水泥基复合材料的研究进展。同时指出, 为促进其在工程中的应用, 对碳纤维水泥石电阻率的离散性、稳定性以及多向约束受力下电阻率的变化曲线等问题都必须进一步深入研究。      

新型加固用智能碳纤维板及感知性能试验

结合碳纤维增强树脂的强度特性与光纤布拉格光栅的传感特性研制开发出具有变形自感知能力的智能碳纤维复合板。在介绍内嵌光纤传感器的碳纤维复合板制作工艺的基础上,利用自制张拉反力架和钢筋混凝土梁进行智能碳纤维板的感知性能试验,获取包括灵敏度、线性度、重复性、迟滞性以及准确度等传感性能指标。研究结果表明:智能碳纤维板具有良好的线性度与重复性,测试精度高,是集感知和受力、功能材料和结构材料于一体的新型土木工程智能材料,既可以方便地作为混凝土结构的加固装配件,又可作为其表面的传感器件,具有良好的工程应用前景。     

土木工程结构用智能感知材料、传感器与健康监测系统的研发现状

随着智能感知材料的发展，高性能传感器及其测试技术为结构智能健康监测系统的研究与发展提供了崭新的途径，结构智能健康监测已经成为诸多领域的前沿研究方向。本文重点介绍了作者近年来基于智能感知材料的智能传感器及土木工程结构智能健康监测系统的研究成果。主要包括：光纤光栅应变和温度传感器与压电薄膜（PVDF）应变和裂缝监测传感器及其性能；无线传感器网络与无线传输技术及其性能与工程应用；碳纤维智能传感器与纤维增强-光纤光栅应变传感器及其性能；智能混凝土与智能混凝土标准应变传感器及其性能；智能健康监测系统及其工程应用。     

粉煤灰水泥混凝土材料水化机理研究

本文从粉煤灰水泥混凝土材料组成成分、水化性能、组成材料间的水化作用等方面进行研究,从而得到粉煤灰水泥混凝土材料水化机理,从而为粉煤灰水泥混凝土在结构工程,尤其在路面工程方面应用,具有现实指导意义。     

硬化期受扰动混凝土的抗硫酸盐侵蚀性能

凝结硬化期间的施工扰动,可能使混凝土产生砂浆微裂缝与骨料位移,进而影响其强度及耐久性.为分析硬化期扰动对混凝土抗硫酸盐侵蚀性能的影响,采用振动台模拟工程扰动,借助超声波和扫描电子显微镜(SEM)等测试手段,系统研究了硬化期受扰混凝土抗硫酸盐侵蚀的劣化规律,探讨了其损伤劣化机理.结果表明:临近初凝(贯入阻力值为3.5～11.5 MPa)和临近终凝(贯入阻力值为19.5～28.0 MPa)的扰动对混凝土影响较小,受侵蚀后试件质量和相对动弹模量的变化规律与未受扰混凝土基本一致.硬化中期(贯入阻力值为11.5～19.5 MPa)的扰动对混凝土性能影响明显,使混凝土抗压强度降低14％,抗折强度降低20％;硫酸盐腐蚀进程中,混凝土质量在90次循环后开始出现明显下降,相对动弹模量在130次循环后出现急剧下降,经250次循环后达到0.60,此时基准混凝土的相对动弹模量仍为0.90;SEM结果表明,受扰混凝土内部微裂纹增多,结构密实性变差,硬化期扰动加速了混凝土在硫酸盐侵蚀环境下的劣化.     

不同种类混凝土涂料的性能测试及对比研究

混凝土结构中大量使用涂料进行防腐蚀和劣化修复,准确掌握涂料的各项性能对于监控其使用效果十分重要.为了能够快速检验和测试混凝土涂料性能的优劣,根据日本土木协会和日本道路协会标准,检测了分别以氟树脂、聚氨酯和环氧为面漆的涂层配套体系的耐碱性、附着强度、耐老化能力和对裂缝的追随性.对各种涂层的性能进行了对比和分析.结果表明,各类涂层均对混凝土底材具有优异的附着能力;耐碱性能具有较大差异;氟树脂涂层具有更好的耐老化能力和更优的裂缝追随性,对混凝土结构的防护效果最佳.     

自感型功能结构研究前沿与展望

目的 对自感型功能结构的研究进展进行归纳和分析,并对其发展前景进行展望。方法 定义自感型功能结构的概念,分析自感型功能结构的设计流程,揭示自感型功能结构的内涵,并从敏感材料、制造方法、响应激励3个视角对自感型功能结构设计的研究进展进行分类,证明其可以通过元胞性能设计、基元构型制造和序构综合调控的设计方法进行制备并应用于实际场景中,实现结构—功能的一体化。结果归纳了自感型功能结构的设计与制造研究进展,总结了自感型功能结构的重点技术和在不同领域的突出性成果,结合自感型功能结构的概念内涵,对其在机械、材料、生物等领域的应用进行了展望。结论自感型功能结构可以对本体和环境的变化进行感知,按照设计好的特定方式发生功能或性能的变化,具有结构构型高效、感知对象多样、感知元件集成等特点,在相关领域中具有广阔的应用前景。     

Concepts and requirements of durability design for concrete structures: an extensive review of CCES01

Acquiring enough durability for concrete structures in their design phase is a crucial step against unexpected deterioration during their service life. This article gives an extensive and in-depth review of the first Chinese national guide, CCES01-2004, destined exclusively for durability design of concrete structures. Based on the state-of-art knowledge on durability and in place experiences, this guide formulates its durability requirements from several fundamental concepts: environmental action, durability limit state and structure service life. For each environmental class and expected service life, the guide details its requirements on raw material constituents, concrete curing conditions, material performance as well as structure details, in particular the concrete cover to reinforcement steel. The relevant quantitative requirements are compared with those from other codes such as EuroCode2, EN206, ACI318 and CSA. As a special case, the durability of post-tensioned prestressed concrete structures is treated separately and a multi-layer, environment-based strategy is proposed for the prestress tendon and anchorage protection. At the end, the remaining crucial questions are brought forth for durability design of concrete structures.     

Modeling of the thermopiezoelastic behavior of prismatic smart composite structures made of orthotropic materials

Asymptotic homogenization models for prismatic smart composite structures are derived and the effective elastic, piezoelectric, and thermal expansion coefficients are obtained. The actuation coefficients characterize the intrinsic transducer nature of active smart materials that can be used to induce strains and stresses in a coordinated fashion. Examples of such actuators employed with smart composite material systems are derived from piezoelectric, magnetostrictive and some other materials. The constituents of the smart structures are assumed to exhibit orthotropic characteristics. The original problem for the regularly non-homogeneous smart composite structure reduces to a system of three simpler types of problem, called unit cell problems. It is precisely these unit cell problems that enable the determination of the aforementioned coefficients. These effective coefficients are universal in nature and can be used to study a wide variety of boundary value problems associated with a smart structure of a given geometry.     

Composites get smart

Intrinsically smart structural composites are multifunctional structural materials which can perform functions such as sensing strain, stress, damage or temperature; thermoelectric energy generation; EMI shielding; electric current rectification; and vibration reduction. These capabilities are rendered by the use of materials science concepts to enhance functionality without compromising structural properties. They are not achieved by the embedding of devices in the structure. Intrinsically smart structural composites have been attained in cement-matrix composites containing short electrically conducting fibers and in polymer-matrix composites with continuous carbon fibers. Cement-matrix composites are important for infrastructure, while polymer-matrix composites are useful for lightweight structures.Smart structures are important because of their relevance to hazard mitigation, structural vibration control, structural health monitoring, transportation engineering, thermal control, and energy saving. Research on smart structures has emphasized the incorporation of various devices in a structure for providing sensing, energy dissipation, actuation, control or other functions. Work on smart composites has focused on the incorporation of a functional material or device in a matrix material for enhancing the smartness or durability, while that on smart materials has studied materials (e.g. piezoelectric) used for making relevant devices. However, relatively little attention has been given to the development of structural materials (e.g. concrete and composites) that are inherently able to provide some of the smart functions, so that the need for embedded or attached devices is reduced or eliminated, thereby lowering cost, enhancing durability, increasing the smart volume, and minimizing mechanical property degradation (which usually occurs in the case of embedded devices).     

Debonding of concrete-epoxy interface under the coupled effect of moisture and sustained load

Fiber reinforced polymer (FRP) is a prevalent material for strengthening or retrofitting concrete structures. It has been found that the effectiveness of entire strengthening or retrofitting scheme highly depends on the bond performance of concrete-epoxy interface. During service life, structures are exposed to complicated and unavoidable mechanical and environmental situations that can cause bond deterioration. In order to ensure the structural safety in a long run, a comprehensive experiment focusing on the coupled effect of sustained load and moisture on the bond property of concrete-epoxy interface is conducted. A drastic deterioration of concrete-epoxy interfacial fracture toughness, up to 77%, is observed under coupled sustained load and moisture exposure. Based on our experimental investigation, a predictive model is developed to describe the bond property variations of concrete-epoxy interface against long-term sustained load and moisture. The proposed predictive model can be used to obtain a more reliable and accurate service life prediction and maintenance planning for FRP-bonded concrete structures.     

Self-Sensing Cementitious Composites with Hierarchical Carbon Fiber-Carbon Nanotube Composite Fillers for Crack Development Monitoring of a Maglev Girder

In view of high-performance, multifunctional, and low-carbon development of infrastructures, there is a growing demand for smart engineering materials, making infrastructures intelligent. This paper reports a new-generation self-sensing cementitious composite (SSCC) incorporated with a hierarchically structured carbon fiber (CF)-carbon nanotube (CNT) composite filler (CF-CNT), which is in situ synthesized by directly growing CNT on CF. Various important factors including catalyst, temperature, and gas composition are considered to investigate their kinetic and thermodynamic influence on CF-CNT synthesis. The reciprocal architecture of CF-CNT not only alleviates the CNT aggregation, but also significantly improves the interfacial bonding between CF-CNT and matrix. Due to the synergic and spatially morphological effects of CF-CNT, that is, the formation of widely distributed multiscale reinforcement networks, SSCCs with CF-CNTs exhibit high mechanical properties and electrical conductivity as well as excellent self-sensing performances, particularly enhanced sensing repeatability. Moreover, the SSCCs with CF-CNTs are integrated into a full-scale maglev girder to devise a smart system for crack development monitoring. The system demonstrates high sensitivity and fidelity to capture the initiation of cracks/damage, as well as progressive and sudden damage events until the complete failure of the maglev girder, indicating its considerable potential for structural health monitoring of infrastructures.     

智能CFRP加固RC梁荷载效应的实时模拟与测评

制备了4 根炭纤维复合材料(CFRP) 加固钢筋混凝土(RC) 实验梁, 并在梁内钢筋、混凝土及加固CFRP中预置了布拉格光栅光纤传感器(FBG) 和电阻应变片两种传感器。根据钢筋混凝土理论和ANSYS 有限元软件编制了实验梁受弯荷载效应模拟计算程序。实验表明, 实验梁在受弯承载过程中, 布拉格光栅光纤传感器与传统应变片有完全一致的线性关系; 模拟计算出的实验梁受拉钢筋、压区混凝土应变值及挠度与荷载的关系与CFRP 中FBG的实测值吻合较好。由于对既成RC 结构不能在内部装置传感器(会破坏结构降低抗力) , 采用智能CFRP 加固RC 结构可实现加固和实时健康测评双重功能。      

FRP-OFBG智能复合筋及其在加筋混凝土梁中的应用

结合纤维增强聚合物(FRP)的强度特性和光纤光栅(OFBG)的感知特性,研制开发出了FRP-OFBG智能复合筋,研究了它的力学、微观结构、感知等特性。通过FRP-OF-BG加筋混凝土梁静载试验,监测了FRP筋的应变和混凝土开裂,研究了FRP筋与混凝土的滑移和混凝土梁的应变分布。结果表明,FRP-OFBG智能复合筋克服了光纤光栅在混凝土中埋设的工艺难题,是集感知和受力、功能材料和结构材料于一体的新型土木工程材料,既可以方便地作为混凝土结构的内部传感元件,也可以作为结构受力筋,具有很好的应用前景。     

碳纤维增强混凝土的拉敏特性及梁构件的机敏监测

碳纤维具有良好的导电性,电阻率变化率与所处应力场具有稳定的对应关系,在混凝土结构中构造一定厚度的碳纤维增强混凝土机敏层,并通过实时监测电阻率变化率,可对结构的实时荷载和变形程度进行预报.本工作研究了碳纤维增强混凝土本征拉敏特性规律,并将其应用于钢筋混凝土梁构件中,实现了对构件实时荷载和变形的在线监测.