【作者】 李福海；

【导师】 赵人达；

【作者基本信息】 西南交通大学 ， 桥梁与隧道工程， 2012， 博士

【摘要】 随着中国基础建设的快速发展,我国在中长期铁路网规划中提出,到2020年全国铁路营业里程达到12万公里,其中桥梁下部主要是以钢筋混凝土作为承重结构。在特殊侵蚀环境中,混凝土耐久性作为保障工程长期质量和运营安全的重要问题受到极大的重视。抗冻性是衡量混凝土耐久性的一项重要指标,在贯穿南北跨越四大水系的京沪高速铁路沿线,大部分地区存在冻融侵蚀环境,线路某些区间地下水还存在严重的盐侵蚀,极有可能造成混凝土结构的损伤,影响到结构安全性,因此开展混凝土抗冻性、抗盐侵蚀性及其附加防护措施的研究具有重要的现实意义。论文在总结了国内外已有的混凝土抗冻性研究及防护措施的基础上,调研了京沪高速铁路沿线城市的气温情况及我国主要城市年冻融循环次数,并调研了京沪铁路沿线桥梁下部结构所处环境中侵蚀离子的浓度。针对京沪高速铁路北线部分桥梁桩基及墩身处于水位线上下部位,既存在冻融循环(D3及D4),又有海水盐浸渍(H3及H4)双重环境进行的抗侵蚀性研究。通过试验实测、数值模拟及微观分析等途径,综合考虑不同强度混凝土试件在冻融环境中,不同侵蚀环境下,混凝土的抗冻性。并开展了两种不同材料的防护试验,包括钢护筒的刚性防护及喷涂聚脲材料的柔性防护。论文工作及得到的结论如下：1、针对京沪铁路实际工程处于冻融侵蚀与盐侵蚀共同作用的环境,本文试验环节设计了C25、C35及C50三种强度等级的高性能混凝土在冻融循环单独作用和与硫酸钠溶液、硫酸钠与氯化钠溶液等因素综合作用下的耐久性试验；并开展了两种类型的防护试验：刚性防护及柔性防护。以质量损失率、强度、动弹性模量、冻胀应力-应变及形貌变化为测试技术指标。通过试验得出无防护试件随着冻融循环次数的增加,混凝土的质量损失越来越大,而经过防护的试件在试验过程中质量逐渐增大,后期趋于平稳；盐溶液冻融循环作用对无防护混凝土的损伤比较严重,以硫酸钠与氯化钠混合溶液最为严重。2、冻融循环作用引起混凝土内部产生周期性变化的应力。混凝土在单次冻融循环过程中随着温度的降低应变逐渐增大,相应的拉应力也越来越大,当温度开始上升时,内部应变逐渐减小,相应的拉应力也越来越小。但在冻融循环过程中混凝土内部的变形并没有完全恢复,而是有残余变形存在,这表明在每次冻融循环作用之后,在混凝土内部均会有损伤产生,损伤不能愈合且逐渐累积。试验比较了高性能混凝土与普通混凝土在冻融循环过程中,表现出不同的损伤现象,并分析了各自冻融破坏的损伤机理。3、钢护筒在温度变化过程中产生环箍压应力,削减了混凝土由于冻融循环作用产生的冻胀应力,使混凝土材料表面由无防护时的受拉状态转变为受压状态,从而起到对混凝土材料的防护作用。刚性材料及柔性材料对混凝土的防护机理不同,但二者均可以阻断或延缓有害盐溶液或水溶液进入到混凝土内部,从而避免混凝土材料的损伤,延长混凝土结构的使用寿命。4、针对混凝土冻融循环作用提出了用变形分量、温差和冻胀引起的变形量表示的应力分量的物理方程。得出在一定的位移边界条件下,弹性体中由于温差和冻胀引起的位移,就等于温度不变而承受由于温差和冻胀引起的外来作用体力时的位移。并根据第一强度理论即最大拉应力理论提出了混凝土在冻融循环过程中损伤开始的判据。5、通过大型通用软件对冻融环境下无防护混凝土及钢护筒防护混凝土温度场及温度应力进行了数值计算分析,得出混凝土不同部位温度场及温度应力的变化规律。通过改变相关参数：结构尺寸、边界防护条件、冻融速率及混凝土强度等级等参数,分别计算了混凝土不同深度处的温度及应力在参数变化时相应的变化规律。6、通过微观结构分析研究了在冻融循环过程中,盐溶液对混凝土损伤的加速作用,并分析了掺合料对改善混凝土性能的作用。本文的研究为提高高性能混凝土的抗冻性、掌握冻融损伤机理及对混凝土结构采用恰当的防护措施作了创新性的工作,为进一步深化研究和全面建立科学的混凝土耐久性评估体系作了大量基础性工作,为高性能混凝土在实际工程中的应用提供了科学依据。更多还原

【Abstract】 With the rapid development of civil construction in China, length of railroad lines in service of nation will reach to120,000km before2020in the layout of medium-term and long-term railway network. The bridge substructure will use reinforce concrete structure as load-carrying members. In the special erosion environment, the durability of concrete which can ensure engineering long-term quality and operation safety gets great attention. Frost resisting property is an important index weighting the durability of concrete. There exists environment of freeze-thaw cycle in most regions along the line of Beijing-Shanghai high speed railway, which runs north and south, acrosses four large water systems. The groundwater of some intervals alone the line contains salt corrosion, which will cause concrete structures damage easily and threat the safety of structures. So, study on frost-resistance and salt erosion properties of concrete and additional protective measures for bridge substructure in freeze-thaw environment have important realistic meaning.The dissertation summarizes research about concrete frost resisting property and protection measures from domestic and overseas. Atmospheric temperature in the line of Beijing-Shanghai high speed railway and times of freeze-thaw cycle of most cities are investigated. The concentration of corrosion ionics around bridge substructure is also investigated. Anti-erosion properties of concrete are studied based on some bridge pile foundations and piers of northern Beijing-Shanghai high speed railway. These bridge substructure are in the waterline, where exist freeze-thaw cycle(D3or D4) and sea water salt erosin.Frost resisting properties of concrete are studied under freeze-thaw cycle and different corrosion surroundings by means of experiments, numerical simulation and micro-analysis. Two different kinds of materials are used to protect concrete, which are steel pipes and spray polyurea elastomer. Main research and mainly conclusions follows:1. Three grades of high performance concrete C25, C35and C50are designed based on freeze-thaw cycle and salt erosion environments where Beijing-Shanghai high speed railway is. The durability experiments are carried out under freeze-thaw cycle and in different solutions containing distilled water, sodium sulfate or sodium sulfate and sodium chloride. Two kinds of protection measures are adopted. They are rigid and flexible protection, respectively. Indexes of samples testing contain mass loss rate, strength, dynamic modulus of elasticity, stress-strain and surface topography. Variation tendency has been acquired after diffetent times of freeze-thaw cycle. Mass loss of non-protectied HPC becomes bigger with the increase of times of freeze-thaw cycle. But the mass of protected samples is gradually increasing primevally and becomes steady in later period. Freeze-thaw cycle in saline solution produces more serious damage to non-protected samples. The erosion of mix solution of sodium sulfate and sodium chloride is most serious.2. Concrete stresses change cyclically with freeze-thaw cycle. Strain and stress increase gradully with lowering of temperature in one freeze-thaw cycle. When temperature increases, the interior strain and stress reduce gradually. But the interior deformation doesn’t recover and there is residual deformation, which shows that damage occurs in the interior concrete after every freeze-thaw cycle. The different defeatures and damage mechanisms are compared between HPC and normal concrete after freeze-thaw cycle.3. Steel pipes produce hoop stress during the change of temperature, which reduces frost heaving stress and make surface layer concrete in tensile condition change to compressive stress state. The mechanisms of rigidity and flexibility protection are different. They can both stop or postpone harmful saline solution or liquor entering into the concrete. These measures can avoid concrete damage and increase service life.4. Deformation component, range of temperature and frost heave distortion are used to represent physical equation of stress component for concrete under freeze-thaw cycle. The displacement of elastic body caused by range of temperature and frost heave distortion under certain displacement boundary conditions equals to the displacement caused by range of temperature and frost heave distortion as additional forces when the temperature is invariant.5. The physical models of concrete subjected to freeze-thaw cycle are set up and the corresponding behaviors are analyzed by ANSYS. The models contain none protected concrete samples and samples protected by steel pipes. Temperature field and temperature stress of different places in the interior concrete are obtained. The changing regulity of temperature and stress in different depth of concrete are calculated by changing parameters which contain structure size, protection conditions, freeze-thaw rate and concrete grade.6. Microscopic tests are carried out to affirm the accelerating effect of saline solution to concrete damage. The effects of admixture are analysed for improving concrete property. A lot of research work has been done to improve HPC frost resisting property, master freeze-thaw damage mechanism and use appropriate protection measures, which is in favour of intensive study and setting up scientific and comprehensive evaluating system of concrete durability. The dissertation provides scientific basis to practical engineering of HPC.更多还原