宁波舟山港主通道混凝土结构耐久性评估与维护技术

系统阐述宁波舟山港主通道跨海工程混凝土结构耐久性评估与维护技术。首先介绍宁波舟山港主通道工程概况及100年使用年限的总体要求;确定耐久性极限状态为海洋氯离子侵入引起的钢筋表面脱钝。针对此极限状态,建立了氯离子侵入过程的耐久性评估模型,确定了不同暴露条件下模型参数的统计规律;根据混凝土保护层厚度的现场实测数据和修正的暴露条件下氯离子扩散系数,对模型参数进行了更新;考虑施工阶段混凝土构件的耐久性附加措施,以某标段非通航孔桥为例,使用全概率方法计算了各类混凝土桥梁构件的失效概率和可靠指标;最终在混凝土构件耐久性评估的基础上,提出了某标段非通航孔桥各类混凝土构件的基本维护制度和维护周期。     

海水环境粉煤灰混凝土结构耐久性现场检测与评估分析

对服役12年的华南某跨海大桥典型构件开展碳化性能、氯离子扩散性能等指标的耐久性检测,评估了海水环境下掺粉煤灰的高性能混凝土长期耐久性。研究表明:随高程的增加混凝土碳化深度逐渐增大,其中大气区浪溅区水位变动区,碳化作用对粉煤灰混凝土结构耐久性的影响较小;粉煤灰可显著提升实体结构混凝土抗氯离子侵蚀性能,粉煤灰高性能混凝土的氯离子扩散系数不大于0.40×10-12m2/s,比普通混凝土氯离子扩散系数降低了约6倍;利用规范计算了引桥承台混凝土中氯离子含量计算值,其计算值与实测值吻合较好,可用于实体工程混凝土结构的耐久性评估,评估结果显示采用粉煤灰高性能的桥梁典型构件满足100年设计使用寿命的要求。     

海洋潮汐浪溅区混凝土表面氯离子浓度计算模型

海洋混凝土结构的表面氯离子浓度反映了海洋氯化物环境的腐蚀作用强度,是海洋混凝土结构耐久性分析和定量设计的重要参数。本文依据国内外不同地区的大量自然暴露试验数据,通过数理统计和回归分析,确定了各种海洋环境条件下表面氯离子浓度的统计特征值,分析了海洋潮汐浪溅区混凝土中氯离子的传输机理和积聚规律,揭示了水胶比对混凝土表面氯离子浓度的影响规律,进而综合考虑水胶比、胶凝材料种类和时变特性等因素的影响,建立了海洋潮汐浪溅区混凝土表面氯离子浓度的改进计算模型。结合国内外各种表面氯离子浓度经验模型的预测结果和海洋自然暴露试验的实测数据,对比验证了所建立表面氯离子浓度计算模型的有效性和适用性,为海洋氯化物环境下混凝土结构的耐久性设计和服役寿命分析提供了重要边界条件。     

氯离子侵蚀对钢筋混凝土构件抗力影响的研究

氯化物是钢筋混凝土结构在使用寿命期内可能遇到的一种最危险的侵蚀介质,混凝土中钢筋表面的氯离子浓度超过一定的限值,钢筋就可能会发生锈蚀,锈蚀的钢筋会导致混凝土构件的承载力下降.通过分析国内外研究者所做的大量工作,讨论了氯离子侵入引起的锈蚀钢筋混凝土构件的抗力计算方法,为氯化物环境条件下混凝土结构的耐久性评估提供参考.     

海洋混凝土结构表面自由氯离子含量时变规律及对其寿命影响

表面氯离子含量(C_s)是研究海洋环境条件下混凝土结构耐久性和服役寿命的氯离子扩散方程的边界条件,是海洋混凝土结构耐久性分析和定量设计的重要参数。依据国内外大量自然暴露试验与工程实测数据,通过采用Excel、Origin等数据分析软件进行数据统计和回归分析,确定了海洋混凝土结构表面自由氯离子含量(C_(sf))与表面总氯离子含量(C_(st))之间的相互关系,探讨了海洋混凝土结构的C_(sf)时变规律,建立了C_(sf)与暴露时间之间的关系表达式及其取值范围,并运用可靠度理论和修正氯离子扩散理论分析了C_(sf)时变性对海洋混凝土结构寿命的影响。结果表明:C_(sf)与C_(st)线性相关,且C_(sf)随着暴露时间的延长呈指数或者幂函数的增长关系;采用不同的C_(sf)时变性规律,对海洋混凝土结构寿命具有重大的影响。     

海港码头混凝土结构干湿交替区域氯离子侵蚀规律研究

基于对乍浦港混凝土结构现场检测数据,分析干湿交替区域氯离子侵蚀状况存在差异的原因,建立表面氯离子浓度和扩散系数随高程、季节、材料、及服役时间的关系,提出基于海域气象条件推定扩散模型统计参数的经验计算公式,并根据设计潮位确定氯离子严重侵蚀区域范围,可为耐久性设计和维护提供理论依据。     

海洋环境中混凝土结构服役寿命预测

通过参数定义对Fick定律的不合理假定进行修正,推导氯离子在混凝土中扩散的多因素修正模型,综合考虑氯离子扩散系数的时随效应、混凝土的氯离子结合能力和混凝土自身缺陷的影响.根据对大量数据的分析试算,给出模型中参数的取值.利用该扩散模型,进一步推导海洋环境下基于概率性能的混凝土结构服役寿命计算方法,有效解决混凝土结构服役寿命预测中氯离子扩散系数及混凝土保护层厚度的随机特性.最后给出实际工程算例,说明该预测方法的有效性.     

海水环境下钢筋混凝土人工鱼礁的耐久性寿命预测

根据人工模拟的流动海水环境(流速约为0.15m/s)下的混凝土侵蚀试验测得的混凝土中氯离子质量分数,分别测定了腐蚀350,380,400d后混凝土的氯离子扩散系数,并计算和预测了混凝土人工鱼礁的耐久性寿命。研究结果表明:氯离子在混凝土人工鱼礁中的扩散规律基本上遵循Fick第二定律;钢筋混凝土人工鱼礁的耐久性寿命与保护层厚度的平方成正比;海水盐度对混凝土人工鱼礁的耐久性寿命影响较大。     

人工鱼礁在自然海水条件下的腐蚀寿命研究

有氯盐侵蚀的钢筋腐蚀,是钢筋混凝土结构性能劣化的主要原因之一,混凝土构件使用寿命的关键是氯离子的传输速率和使钢筋产生锈蚀的时间。本文以人工鱼礁混凝土构件为研究对象,分析海水氯离子在C30、C35和钢渣复合材料人工鱼礁混凝土中的扩散系数,以混凝土中钢筋锈蚀的临界氯离子浓度为寿命预测的边界条件,利用氯离子扩散模型预测C30、C35和钢渣复合材料人工鱼礁在海水中的腐蚀寿命。研究结果表明,氯离子在混凝土人工鱼礁中的扩散规律基本满足Fick第二定律。通过模型计算得出C30、C35和钢渣复合材料混凝土人工鱼礁的腐蚀寿命分别为51.6,54.8和56.8年。     

氯盐干湿环境下受弯横向裂缝对钢筋混凝土耐久性影响

为了研究持续开裂状态下横向裂缝对钢筋混凝土结构耐久性的影响特性,开展了8根受弯开裂钢筋混凝土梁构件的盐溶液干湿循环试验;借助无损检测技术和破损实测方法,分别对氯离子侵入量、钢筋半电池电位、腐蚀电流密度以及平均锈蚀率等进行了对比分析。研究结果表明,裂缝的存在将提高混凝土的渗透性,裂缝处及周围混凝土内的氯离子含量明显增大;对于一定裂缝分布状况的钢筋混凝土试验梁,内部钢筋的腐蚀电位、腐蚀电流密度以及平均锈蚀率均高于裂缝自愈及无裂缝的试验梁,并受到保护层厚度与裂缝开展状态的影响,其影响规律可用单位长度内的平均裂缝宽度与保护层厚度的比值wm/c来进行综合评价。综合试验结果,初步建议海洋干湿侵蚀环境下钢筋混凝土构件的最大裂缝宽度wmax宜小于0.003 3 c,相关结论可为海洋混凝土结构的耐久性设计提供参考。     

Probabilistic lifetime assessment of marine reinforced concrete with steel corrosion and cover cracking

In order to study the durability behavior of marine reinforced concrete structure suffering from chloride attack,the structural service life is assumed to be divided into three critical stages,which can be characterized by steel corrosion and cover cracking.For each stage,a calculated model used to predict the lifetime is developed.Based on the definition of durability limit state,a probabilistic lifetime model and its time-dependent reliability analytical method are proposed considering the random natures of influencing factors.Then,the probabilistic lifetime prediction models are applied to a bridge pier located in the Hangzhou Bay with Monte Carlo simulation.It is found that the time to corrosion initiation t0 follows a lognormal distribution,while that the time from corrosion initiation to cover cracking t1 and the time for crack to develop from hairline crack to a limit crack width t2 can be described by Weibull distributions.With the permitted failure probability of 5.0%,it is also observed that the structural durability lifetime mainly depends on the durability life t0 and that the percentage of participation of the life t0 to the total service life grows from 61.5% to 83.6% when the cover thickness increases from 40 mm to 80 mm.Therefore,for any part of the marine RC bridge,the lifetime predictions and maintenance efforts should also be directed toward controlling the stage of corrosion initiation induced by chloride ion.     

基于广义扩散方程海工混凝土结构耐久寿命概率评估方法

针对国内现有的氯离子侵蚀寿命预测模型存在的问题,提出了基于广义扩散方程(GDF)的海洋环境下混凝土结构耐久寿命预测的概率方法.以某海上混凝土工程原位取粉测试及室内快速试验为手段,获得不同环境分区的时变模型参数统计值.采用随机抽样方法,实现结构各部位混凝土使用寿命的概率预测.通过对模型参数的敏感性分析讨论了该模型的优点.最后,提出了周期性检测,不断更新模型参数的动态寿命评估思路.     

海洋环境中温湿度变化对混凝土氯离子传输研究

氯离子渗透到混凝土内部诱发钢筋锈蚀是海洋钢筋混凝土面临的耐久性关键问题。构建考虑骨料、浆体集料界面区的混凝土模型,建立了环境温度、湿度影响的氯离子传输模型,基于COMSOL数值模拟软件分析了材料、环境对混凝土氯离子传输的影响规律,并通过试验进行了验证。结果表明:模拟结果和试验数据具有较高的吻合度;随着温度的升高,氯离子扩散加快,而混凝土中氯离子的渗透深度随着内部湿度的增大而呈现减小趋势。混凝土中高致密骨料存在阻碍了氯离子传输,但界面区存在使得氯离子沿界面区传输并在骨料背后形成传输前锋。     

Probabilistic Durability Assessment of Concrete Structures in Marine Environments: Reliability and Sensitivity Analysis

A probabilistic framework for durability assessment of concrete structures in marine environments was proposed in terms of reliability and sensitivity analysis, which takes into account the uncertainties under the environmental, material, structural and executional conditions. A time-dependent probabilistic model of chloride ingress was established first to consider the variations in various governing parameters, such as the chloride concentration, chloride diffusion coefficient, and age factor. Then the Nataf transformation was adopted to transform the non-normal random variables from the original physical space into the independent standard Normal space. After that the durability limit state function and its gradient vector with respect to the original physical parameters were derived analytically, based on which the first-order reliability method was adopted to analyze the time-dependent reliability and parametric sensitivity of concrete structures in marine environments. The accuracy of the proposed method was verified by comparing with the second-order reliability method and the Monte Carlo simulation. Finally, the influences of environmental conditions, material properties, structural parameters and execution conditions on the time-dependent reliability of concrete structures in marine environments were also investigated. The proposed probabilistic framework can be implemented in the decision-making algorithm for the maintenance and repair of deteriorating concrete structures in marine environments.     

Effect of Fly Ash on Frost-Resistance and Chloride Ions Diffusion Properties of Marine Concrete

It is necessary to pay more attention to the durability of concrete undergoing freeze-thaw cycles and seawater attack simultaneously.Investigated are the effects of water-binder ratio,fly ash (FA) contents and air-entraining agent on resistance to frost and chloride diffusion of marine concrete blended with FA in natural seawater.The results show that fly ash does not improve the frost resistance of concrete but can improve its resistance to chloride diffusion by addition of less than 30%.The resistance to frost and chloride diffusion of FA concrete can be improved with the decrease of water-binder ratio,and FA may improve both of them simultaneously only being mixed with air-entraining agent.A ratio (named as R) of the frost-resisting durability factor to chloride diffusion coefficient can be used to evaluate the durability of marine concrete.Scanning electron microscope (SEM) analyses are consistent with the evaluations by the value of R.     

上海洋山建港后港域夏季水文泥沙状况分析

对2007年9月17-26日在上海洋山港海域固定观测点(平均水深13 m)观测得到的水文泥沙要素,以及悬沙和底质样品分析.分析结果为:1)港域有效波高0.21-1.37 m(风速0.6～14.0 m/s),平均0.61 m(平均风速5.5 m/s).平静天气(平均风速小于5.0 m/s)下,波高随水深变化,两者的相关系数为0.899;而在强风天气下,波高受风况控制.2)最大表层流速超过2.00 m/s.大潮涨潮流占优势,小潮时落潮流占优势;与北岛链汉道封堵前相比,大潮涨、落潮平均流速分别减小15%和30%,小潮涨、落潮平均流速均减小30%～40%.各层余流均为西北方向,与涨潮流方向一致;垂向平均余流速0.11 cm/s,表层达0.25 m/s.3)离底高程1.35 m层和0.35m层最大悬沙浓度均大于3 kg/m3,两层平均悬沙浓度分别为0.89和0.95 kg/m3.无论大潮还是小潮涨潮悬沙浓度均大于落潮,这种现象在大潮时更为显著,潮周期中最大悬沙浓度出现在涨急.与工程前相比悬沙浓度明显降低,大、小潮降低均达20%.4)港区底质平均粒径9.0μm,工程后有变细的趋势.     

Assessment of structural stability in Bohai Sea area based on AHP-GDM model

The AHP-GDM model is used for the assessment of structural stability, with the Bohai Sea area as an example. In this model, the credit degree of each expert is calculated through the assessment matrix based on the similarity and diversity of vector. The comprehensive opinions of expert panel are quantitatively obtained by considering the effect of credit degree. According to the geological structural setting, the Bohai Sea is divided into twelve assessment zones of structural stability by non-uniform element method. The structural stability grade of each zone is obtained on the basis of the latest geophysical data, earthquake statistical data, and the information of fault activities, current stress field and crustal deformation. The results show that there are one relatively stable area, three relatively sub-stable areas, six relatively sub-unstable areas and two relatively unstable areas. The assessment results of non-uniform element method are very close with those of uniform grid method with size of 0.25° in longitude direction and 0.14° in latitude direction. However the workload of non-uniform element method is only 1/16 of the latter. Compared with traditional assessment methods of structural stability, a more objective and reliable assessment result can be obtained by combining non-uniform element method and AHP-GDM model.