不同环境条件下混凝土构件氯离子侵蚀试验

为研究不同环境条件下混凝土构件氯离子侵蚀劣化规律,开展弯拉应力构件的氯离子浸泡侵蚀试验和无应力构件的盐雾侵蚀试验.基于氯离子质量分数、构件弯拉强度及弯拉应变等测试结果,研究了侵蚀时间、环境温度、应力水平、环境氯离子质量分数及侵蚀方式等因素对氯离子扩散特征和构件抗弯性能的影响.试验结果表明:浸泡环境中混凝土内部氯离子质量分数较盐雾环境高;试件内部氯离子质量分数随腐蚀时间、环境温度、环境氯离子质量分数及应力水平的增大而增大;氯离子扩散系数随应力水平和环境温度的提高而增大;在较低应力水平、较低环境温度和较短的侵蚀时间内,混凝土构件极限弯拉强度有小幅度上升趋势,然后随侵蚀时间的增长而衰减;混凝土构件的极限弯拉应变随各影响因素的增大而降低.研究结果可为钢筋混凝土构件在氯盐侵蚀环境下的耐久性评估及设计提供依据,具有一定工程实际意义.     

海洋大气区氯离子在混凝土中的沉积与传输行为研究综述

海洋大气区氯离子对钢筋混凝土的侵蚀行为可分为两个阶段,首先,氯离子在风力作用下附着在混凝土表面,其次,从混凝土表面向混凝土内部侵蚀。基于海洋大气区氯离子对混凝土侵蚀的全过程,对已有研究进行归纳总结,阐述了各影响因素对沉积过程的影响规律。其中,海水含盐量、风速、暴露时间与混凝土氯离子沉积量呈正相关关系,距海岸距离与混凝土氯离子沉积量呈负相关关系;论述了各影响因素对传输过程的影响规律,水灰比越大、暴露时间越长、温度越高、内外湿度梯度越大、碳化越严重越容易形成对流区。目前,针对海洋大气区氯离子在混凝土中沉积和传输行为开展研究多基于单因素,多因素耦合作用下的沉积和传输行为尚需进一步研究。     

海洋大气中氯离子在粉煤灰混凝土中的传输规律

为了实现海洋大气环境中粉煤灰混凝土耐久性使用寿命的预测,从氯离子在人工模拟海洋大气环境中粉煤灰混凝土中的传输试验出发,结合氯离子在非饱和多孔介质中的传输机理,研究海洋大气环境下混凝土内部微环境（微环境温度和相对湿度）及粉煤灰掺量对氯离子传输速率的影响程度,并与人工模拟海洋水下环境试验结果进行对比分析.研究结果表明：1) 在海洋大气环境与海洋水下环境下,氯离子在粉煤灰混凝土中的扩散模型形式上一致,粉煤灰的掺入对氯离子传输能力有一定的影响,但不会改变氯离子在混凝土中的传输机理.2) 当粉煤灰掺量一定时,微环境相对湿度越高（微环境温度一定）,海洋大气环境氯离子扩散系数越大;但微环境温度(微环境相对湿度一定)对海洋水下环境和海洋大气环境中氯离子迁移的影响程度不同.3) 粉煤灰掺量(微环境温度、相对湿度一定)对海洋水下环境和海洋大气环境氯离子扩散系数的影响规律不同.     

Non-steady state chloride migration and binding in cracked self-compacting concrete

We adopted a notch method to study the influence of crack width (macro level) on chloride transport and binding of cracked concrete under a non-steady state migration test. The results show that migration coefficient of cracked concrete increases with increasing crack width up to a critical value (0.43 mm), for the whole concrete or the area close to crack; the increase of migration coefficient could be independent from crack parameter when a critical crack width is reached. For chloride binding, Langmuir isotherms of cracked concrete samples exhibit the similar decreasing trend as crack width increases from 0.27 to 1.96 mm. The increased current value could be responsible for the trend based on the hypothesis of electric force.     

Effects of external D. C. electric fields on friction and wear behavior of alumina/brass sliding pairs

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型钢混凝土梁式转换节点抗震性能研究

通过对连续型钢混凝土梁式转换层结构模型的两种加载方式下的拟静力试验,对比分析了型钢混凝土转换节点与柱不带轴压力型钢混凝土框架节点的抗震特性,得到了不同于普通框架节点的转换节点的破坏机制、耗能能力、强度退化等.分析得出节点型钢腹板的剪应力方程,利用试验数据可求得腹板上测点的应力值.为了与试验结果相互验证,建立有限元模型,进一步对比分析证明了转换节点在地震力下的受力特性符合节点斜压杆机理.     

单轴受压混凝土的微裂缝和氯离子侵入性

采用1种无破损微裂缝估算指标-比裂缝面积来评价单轴压力作用下混凝土棱柱体的扩展微裂缝。加压卸载后试块暴露于氯离子环境中,测得试块中的氯离子含量分布。分析了单轴压力下混凝土微裂缝的发展以及荷载、微裂缝和氯离子渗透性的相关规律。试验结果表明,在大约0.3的应力水平范围内,受压并卸载后的试块表观氯离子扩散系数普遍降低,但随着应力水平的继续提高,氯离子扩散性能开始提高并超过未加载时的氯离子扩散系数。混凝土在单轴受压并卸载的情况下,其微裂缝的发展和恢复与应力水平关系密切。比裂缝面积能够较好地表征混凝土中微裂缝的发展,有助于分析混凝土在荷载作用下产生的微裂缝对氯离子传输性能的影响。     

Assessment on Chloride Contaminated Resistance of Concrete with Non-steady-state Migration Method

A preparation technology of ctdoride contaminated resistant concrete was presented. The newly developed non-steady-state migration test method was employed for the evaluation of chloride ions diffusion coefficient of the concrete. The experimental results show that this method has a good correlation with the traditional NT Build 443 method, and it provides an effective and quick approach to assess the resi,resistant capacity of concrete aginst chloride ions.     

Simulation of Fatigue Stiffness Degradation in Prestressed Concrete Beams under Cyclic Loading

In order to investigate and research the fatigue cracking of prestressed concrete fatigue properties and loading and stiffness degeneration process,cyclic loading tests were carried out on six prestressed concrete beams and the stiffness degradation under fatigue was investigated. A simulation model of stiffness degradation is proposed based on the stiffness analysis of the fatigue-damaged section. The elastic modulus of damaged concrete and the effective residual area of steel were introduced as well as an adjusted three-stage concrete fatigue damage evolution model. The strip method was used to analyze concrete damage due to changing stress along the depth of the beam section. The simulation and test results were compared and a method of predicting fatigue deflection was presented based on the simulation model. The predicted results were compared with that of the neural network method. It is in good agreement for the simulation results with the test results. It is only less than 5% error for the simulation model which can reveal the two-stage degradation of prestressed concrete beams under cyclic loading. It is more precise for the simulation prediction method under proper conditions.     

Modeling the Synergetic Effect of Various Factors on Chloride Transport in Nonsaturated Concrete

Diffusion has been systematically described as the main mechanism of chloride transport in reinforced concrete(RC) structure, especially when the concrete is in a saturated state. However, the single mechanism of diffusion is not able to describe the actual chloride ingress in the nonsaturated concrete. Instead, it is dominated by the interaction of diffusion and convection. With the synergetic effects of various factors taken into account, this study aimed to modify and develop an analytical convection- diffusion coupling model for chloride transport in nonsaturated concrete. The model was verified by simulation of laboratory tests and field measurement. The results of comparison study demonstrate that the analytical model developed in this study is efficient and accurate in predicting the chloride profiles in the nonsaturated concrete.     

混凝土渗透性的原位测试与评价

利用离子迁移实验和混凝土表面电阻率两种实验方法原位测试5种钢筋混凝土箱梁保护层混凝土的氯离子扩散系数和混凝土表面电阻率,讨论原位测试结果与实验室里ASTM C1202电通量测量值的相关性,建立保护层混凝土氯离子扩散系数与混凝土表面电阻率之间的数学关系式,利用原位测试的氯离子扩散系数评价了钢筋混凝土箱梁在海洋环境条件中的使用寿命。研究结果表明,在稳态下混凝土结构表面保护层混凝土的氯离子扩散系数和混凝土表面电阻率与6h电通量具有较好的相关性,可以采用离子迁移实验和混凝土表面电阻率两种实验方法进行在原位测试和评价混凝土的渗透性,混凝土表面电阻率在工程应用上更为简便。     

混凝土中氯离子扩散数值研究

针对混凝土氯离子扩散系数以及表面氯离子浓度受时间效应的影响,采用COMSLOL有限元软件对氯离子扩散过程进行数值模拟,将预测结果与实测试验结果相比较,验证该方法是一种有效的氯离子扩散分析方法.考虑实际环境中氯离子扩散受时间因素及不同氯侵蚀环境因素影响,分别对不同水灰比及不同龄期下的混凝土氯离子扩散进行模拟,为分析近海和除冰盐环境下结构混凝土中氯离子浓度分布提出了一种新的预测方法.     

Water absorption and chloride ion penetrability of concrete damaged by freeze-thawing and loading

In order to investigate water and chloride ion transport in damaged concrete, three types of concrete were prepared, freeze-thawing (F-T) cycling and compressive loading were adopted to induce damage to concrete. Ultrasonic pulse velocity technique was used for evaluating the damage degree of concrete, and the defects of damaged concrete were also detected by X-CT. Water absorption and chloride ion penetrability were used for describing the transport properties of damaged concrete. Effects of damage degree on the water absorption rate and chloride ion penetrability were investigated in detail and the relationships were also established. The results show that the water absorption of concrete makes various responses to damage degree due to the difference of concrete type and damage method. For same concrete with similar damage degree, the water absorption rate of F-T damaged concrete is usually larger than that of concrete damaged by loading. The chloride ion penetrability of damaged concrete increases linearly with increasing damage degree, which is more sensitive to damage degree if the original penetrability of sound concrete is higher.     

二次高温养护对高强混凝土抗Cl^-渗透性的影响

利用氯离子快速渗透法（RCM）研究了普通蒸汽养护后（80℃,0.1 MPa）再进行压蒸（180℃,1 MPa）养护,即二次高温养护,对不同胶凝材料体系的高强混凝土抗Cl-渗透性的影响。结果表明：对于纯水泥混凝土,与标养相比,＂蒸养-压蒸＂养护使混凝土抗Cl-渗透性能劣化。掺入粉煤灰、矿粉以及硅灰以等比例取代水泥时,＂蒸养-压蒸＂都较为充分地激发了上述混合材的火山灰活性,但不同掺合料对＂蒸养-压蒸＂后高强混凝土抗Cl-渗透性能影响差别较大。XRD和SEM研究表明上述结果的产生与高温下水化产物的种类和分布有关。     

饱和状态下开裂混凝土内的氯离子输运

为得出饱和状态下氯离子在开裂混凝土内的输运规律,将饱和状态分为溶液静止和溶液流动2种情况;同时分别考虑表面氯离子质量分数与氯离子扩散系数的时变性和氯离子在混凝土内的线性结合理论,对前者采用传统的双重孔隙介质模型,对后者则采用二维扩散模型进行分析.基于Fick第二定律得出氯离子在裂缝和开裂附近混凝土内输运的计算方程,并根据裂缝自愈的影响对2种模型进行了修正.分别采用这2种模型对所设计的氯离子在预开裂混凝土试件内的侵蚀进行了计算.对比裂缝附近不同时间混凝土内氯离子质量分数的试验结果表明：短期侵蚀采用2种模型计算的结果均接近于试验值,长期侵蚀采用二维扩散模型能得到更加精确的结果.该结果为氯盐侵蚀下的混凝土结构耐久性设计与评估提供了参考.     

中型混凝土空心砌块多层房屋的抗震性能研究

通过对14片中型混凝土空心砌块墙片进行系统的抗侧力性能试验研究,提出了墙体抗剪计算公式,并通过非线性地震反应分析,对中型混凝土空心砌块多层房屋的抗震性能作出了较为客观的评估。     

钢筋脱钝氯离子阈值快速测定新方法

为了缩短钢筋脱钝氯离子阈值试验测试周期,基于混凝土中氯离子在电场加速作用下快速迁移的特性,提出一种钢筋脱钝氯离子阈值快速测定方法.该测试方法主要存在两大技术问题：外加电场电压确定和钢筋脱钝时刻的判别.为了证明该试验方法的可行性,设计了自然渗透实验进行对比.实验结果表明：电场加速实验能有效区分不同掺合料对氯离子阈值的影响.研究发现,由自然渗透实验测得的氯离子阈值略大于电场加速实验得到的氯离子阈值,两者比值为1.1～1.3,从而验证了该加速实验方法的可行性.     

混凝土防腐涂料抗氯离子侵蚀性能试验研究

采用电量法和盐溶液干湿循环法对混凝土防腐涂料的抗氯离子侵蚀性能进行了试验研究;并以电量法的通电量比和干湿循环法的18次循环时氯离子侵蚀深度为衡量指标,建议了具有一定工程适用性的混凝土防腐涂料抗氯离子保护性能的评定标准。结果表明：根据电量法的通电量比和盐溶液干湿循环法的氯离子侵蚀深度都能对混凝土防腐涂料的抗氯离子侵蚀性能做出有效评价;干湿循环法能反映防腐涂料在试验过程中的劣化趋势,而电量法无法实现这一点;复合型防腐涂料优于单一涂层涂料,成膜型涂料优于单一渗透型涂料。     

钢管混凝土在高温作用下温度场的非线性有限元分析

利用有限元法计算钢管混凝土在高温作用下的温度场，计算结果与试验结果吻合良好，从而为进一步研究钢管混凝土的耐火极限和高温下的力学性能创造了条件。     

The transport properties of concrete under the simultaneous coupling of fatigue load and environment factors

A set of coupling experimental instrument was designed to study the transport properties of chloride ion in concrete under simultaneous coupling action of fatigue load and environmental factors. Firstly the water-saturated performance of modern concrete was investigated, then diffusion performance of chloride ion under different stress levels and different temperature were studied respectively; meanwhile, the time-dependent behavior of the chloride ion diffusion in concrete was also researched. The results showed that the saturation degree of concrete can reach as high as 99%. Besides, diffusion coefficient of chloride ion increased with increasing of the stress level and temperature, and when the stress level and temperature are at 0.6 and 60 ℃ respectively, the diffusion coefficient is 6.3×10-14 m2/s, moreover the diffusion coefficient of chloride ion in concrete decreased with time under the simultaneous coupling action of fatigue load and environment factors.