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采用化学结合水法、氯离子快速测定法(RCM法)和混凝土成熟度测定法研究了56 d龄期内混凝土氯离子扩散系数和混凝土成熟度的关系。结果表明:混凝土氯离子扩散系数不仅随养护龄期的延长而降低,还随养护温度的升高而降低,延长养护龄期或提高养护温度均可提高胶凝材料的水化程度;室内养护混凝土试件的氯离子扩散系数与混凝土成熟度值之间呈幂函数关系,二者具有很好的相关性(R2=0.976),利用室外养护混凝土试件的数据进行验证计算,其理论计算值与实测值具有较好的吻合性,可根据混凝土成熟度实测值预测出混凝土的氯离子扩散系数;在本工程中,沉管隧道接触海水时混凝土成熟度的推荐值为21064℃·h,控制边界值为13926℃·h,考虑外部养护温度和水化热对混凝土成熟度产生影响时,可对混凝土接触海水的龄期通过后计算进行适当的调整。 相似文献
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通常混凝土构件均处于受力状态,而对自由状态的混凝土试件开展耐久性研究很难真实地反映出混凝土构件的耐久性状况。本研究采用施加恒定压荷载和弯曲荷载的方式,研究荷载对混凝土抗氯离子渗透性能的影响。结果表明:混凝土试件纯受弯段的氯离子浓度随弯曲应力水平的提高而增大,且混凝土内的氯离子渗透深度随应力水平的增加而增大。试件距暴露面相同深度处的氯离子浓度随着压应力水平的提高先减少后增大。混凝土试件的氯离子扩散系数随压应力水平提高而先减少后增大,压应力水平较低时可提高混凝土的抗氯离子渗透性能。对于典型的海洋工程高性能混凝土配合比,混凝土试件的弯曲应力与其恒定荷载影响因子之间呈近似指数函数关系,在混凝土结构耐久性设计中应考虑弯曲荷载对氯离子扩散系数的影响。 相似文献
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为满足海洋环境下高性能混凝土的施工要求,开展了复掺粉煤灰与石灰石粉海工自密实高性能混凝土的试验研究。试验结果表明,在复掺粉煤灰和石灰石粉掺量为40%的条件下,掺入10%~30%粉煤灰自密实混凝土具有较高的流动性、填充性、间隙通过性和抗离析性等工作性,满足自密实混凝土的施工要求;28 d抗压强度大于50 MPa,56 d的电通量小于1 000 C,90 d扩散系数小于1.5×10-12 m2/s,具有较高的抗压强度和抗氯盐侵蚀性能,满足海洋环境下抗氯盐侵蚀的耐久性要求。 相似文献
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为满足海洋环境下高性能混凝土的施工要求,开展了复掺粉煤灰与矿渣粉海工自密实高性能混凝土的试验研究。试验结果表明,在复掺粉煤灰和矿渣粉掺量为60%~70%的条件下,掺入20%~30%粉煤灰自密实混凝土具有较高的流动性、填充性、间隙通过性和抗离析性等工作性,满足自密实混凝土的施工要求;28 d抗压强度大于50 MPa,56 d的电通量小于1 000 C,90 d扩散系数小于1.5×10-12 m2/s,具有较高的抗压强度和抗氯盐侵蚀性能,满足海洋环境下抗氯盐侵蚀的耐久性要求。 相似文献
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大管桩现场取样分析与耐久性研究 总被引:2,自引:0,他引:2
采用现场取样与室内化学分析相结合的方法,研究海洋环境下大管桩的耐久性能。通过对深圳、连云港和宁波3个地区服役1~17 a的大管桩展开耐久性调查,同时在潮差区和浪溅区的桩身混凝土钻芯取样,采用化学分析的方法测试不同深度混凝土中的氯离子含量,计算混凝土氯离子扩散系数,进而经统计分析得出桩身混凝土的腐蚀参数。通过对比研究桩身混凝土与桩帽节点混凝土的抗氯离子渗透性能的差异,研究裂缝对氯离子渗透的影响及大管桩接头处FRP包覆层对接头耐久性的影响。取样研究过程中未发现任何箍筋和主筋锈蚀的现象,服役10~15 a的大管桩箍筋表面氯离子浓度在0.1%~0.2%,箍筋表面光洁如新。 相似文献
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外加电流方式电化学脱盐能够有效脱除混凝土内的有害氯离子,但对预应力钢筋混凝土结构不适用,存在可能引起氢脆和减小握裹力的危险以及安装施工、管理不方便和在脱盐期间现场需要有专业技术人员进行操作等缺点;使用牺牲阳极方式电化学脱盐法将钢筋混凝土内的有害氯离子脱除出来,可以克服上述缺点,既适用于普通混凝土,又适用于预应力混凝土。研究通电时间、脱盐装置位置以及取样深度对牺牲阳极方式电化学脱盐效果的影响。结果表明,牺牲阳极方式电化学脱盐在工作3个月后仍能有效地将混凝土内的氯离子迁移到外部的活性填充材料中,且在距阳极500 mm处脱盐效率最高,能达到脱除混凝土试件内有害氯离子的目的,其中混凝土试件表层脱盐效率最高可达60%左右。 相似文献
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The exposure temperature significantly affects the diffusion of chloride ions in concrete, and, as such, it must be taken into consideration in the development of service-life prediction models for structures exposed to chloride-bearing environments. Most of the earlier studies have used cement paste to assess the effect of exposure temperature on chloride diffusion. In the reported study, chloride diffusion in Type I and fly ash (20% fly ash) cement concrete was evaluated under field and laboratory conditions. The laboratory concrete specimens were exposed to chloride solution maintained at four temperatures (22, 35, 50 and 60 °C) for 365 days. Beam specimens were exposed in the tidal zone of a marine exposure site, along the Arabian Gulf coast, for up to 10 years to study the chloride diffusion in the field specimens. The coefficient of chloride diffusion (Da) in the concrete specimens exposed to 22 or 35 ᵒC in the laboratory was less than that in the concrete specimens exposed to 50 and 60 ᵒC. The Da for Type I cement concrete specimens increased by 3.6 times as the temperature was increased from 22 to 60 ᵒC while this increase was 2.3 times for the fly ash cement concrete specimens for a similar increase in the temperature. The Da decreased with the period of exposure in the field specimens. The values of activation energy that can be used for predicting the chloride diffusion for exposure temperature within the range of 22–60 °C were developed based on the laboratory data. In addition, mathematical models were developed relating the coefficient of chloride diffusion in the field and laboratory concrete specimens. The developed models can be utilized to ascertain chloride diffusion in field specimens, utilizing the laboratory values, and hence calculate the useful service-life of structures. 相似文献
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The interfacial bonding performance between seawater sand concrete and basalt fiber reinforced polymer (BFRP) bars were tested under different textile reinforced concrete (TRC) confinement layers, confinement sequences and chloride salt dry-wet cycles. The results show that TRC confinement can change the failure mode of the specimen and improve the ductility of specimens. With the increase of corrosion age, compared with the specimens with the same restrained layers in the conventional environment, the ultimate bond strength of restrained specimens before corrosion gradually decreases, and the slip value when reaching the ultimate bond strength also slightly decreases. The bond strength of the pre-restrained corroded specimens has the same development trend. Based on the bond-slip model of deformed steel bars and concrete proposed by Eligehansen for the first time in 1983—BPE model, under the control of TRC confinement and corrosion age, the relationship between the TRC confinement layer and the ultimate bond strength and slip of seawater sand concrete and BFRP steel bar is established. By fitting and predicting the ultimate bond strength, corresponding slip value, and corrosion age control of different TRC confinement layers, it is found that the confinement effect will not be significantly improved when the confinement layers exceed 4 layers. Under long-term chloride corrosion, the failure mode of the specimen may still change into splitting failure when the number of restrained layers is small. 相似文献
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透水模板在盐田港区三期工程中的应用研究 总被引:9,自引:1,他引:8
在盐田港区三期工程中,对透水模板进行了试验研究并在工程中应用。试验研究和应用结果表明,透水模板能显著改善混凝土的表面质量,有效提高混凝土的耐久性。 相似文献
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通过现场暴露物理试验,实测得到了港口工程混凝土及相对应的水泥砂浆试件中氯离子的浓度分布结果,经回归分析分别得到了这两种试件的氯离子扩散系数。以此为基础,定量评估了粗骨料的稀释、曲折和界面过渡区效应对混凝土中氯离子扩散系数的影响,并建立了混凝土界面过渡区氯离子扩散系数模型。基于混凝土中氯离子扩散的细观数值模拟方法,验证了所建立的混凝土界面过渡区氯离子扩散系数模型的正确性。对细观数值模拟结果的分析可知:界面过渡区对混凝土中仅考虑粗骨料的稀释和曲折效应的氯离子扩散系数的提升效应不可忽略,应充分考虑界面过渡区的存在对混凝土中氯离子浓度分布和扩散特性的影响。 相似文献