弯曲应力作用下钢纤维混凝土氯离子侵蚀性能

研究弯曲应力作用下钢纤维混凝土的氯离子侵蚀性能,分析了钢纤维掺量、弯曲应力水平对混凝土氯离子含量、氯离子扩散系数的影响规律.结果表明,钢纤维的存在能改善弯曲应力作用下的氯离子侵蚀性能,钢纤维掺量为1.5％时,改善效果最明显.弯曲应力的存在加速了氯离子在钢纤维混凝土中的扩散速度、增大了混凝土氯离子含量,应力水平越大时影响越明显.钢纤维混凝土氯离子扩散系数与应力水平间存在指数型数学关系式,最终建立了钢纤维混凝土氯离子扩散系数随应力水平变化的数学模型.     

轴心受压FRP约束圆形混凝土柱应力-应变模型

外包纤维复合材料(FRP)可以有效的提高混凝土柱的承载力和延性.本文系统总结了现有的几种FRP约束混凝土柱应力-应变模型,通过对已有大量试验研究结果的分析,指出FRP约束圆形混凝土柱的性能主要取决于FRP对混凝土柱的约束效果,引入约束效应系数ξ.并以约束效应系数ξ为主要参数,提出了FRP约束圆形混凝土柱三阶段应力-应变模型.该模型能较好的反映FRP约束混凝土柱应力-应变关系的特点,模型计算结果与试验数据吻合较好.     

考虑冻融损伤的钢筋混凝土桥梁氯离子侵蚀寿命预测研究

松花江公路大桥位于东北严寒地区,冬季时,为保障桥梁运行畅通,将在桥面上撒化冰盐以清除积雪,防止结冰,避免大桥混凝土结构遭受氯离子侵蚀和冻融循环的作用.冻融循环作用不仅会造成混凝土构件表面剥落,内部劣化,同时还加速了氯离子的侵入,从而导致混凝土中的钢筋过早脱钝、锈蚀,进而导致构件承载能力下降,结构安全性能降低.对松花江大桥进行了不同冻融损伤下的氯离子侵蚀规律试验研究,在此基础上,对大桥进行了不同冻融损伤下的氯离子侵蚀寿命预测,为大桥的后期使用和维护提供了科学依据.     

基于AHP法和模糊综合评价的钢筋混凝土桥梁耐久性评估

目前,由于耐久性不足造成钢筋混凝土桥梁结构劣化损伤的现象日益严重,为确保既有桥梁的安全、持久运营,必须对其进行科学的耐久性评估,根据评估结果提出合理的维护加固建议.将层次分析法和模糊综合评价应用于既有钢筋混凝土桥梁耐久性评估,提出了一种针对钢筋混凝土连续梁桥的耐久性指标体系及评估模型,同时,利用实际工程的检测数据对其进行了验证,为今后既有桥梁耐久性评估提供了理论依据.     

弯曲应力作用下喷射混凝土抗碳化性能研究-研究生论坛

为了研究隧道喷射混凝土衬砌的碳化规律,采用快速碳化试验方法,研究了不同弯曲应力(0、0.25、0.5及0.75)作用下喷射混凝土及钢纤维喷射混凝土抗碳化性能,在考虑弯曲应力、钢纤维掺量、施工方式基础上对普通混凝土碳化深度预测模型进行修正。结果表明：混凝土碳化深度服从Fick第一定律,扩散系数随应力水平的增加而增加;喷射混凝土碳化深度明显小于普通混凝土,而钢纤维的加入进一步提高喷射混凝土抗碳化性能。通过对碳化后喷射混凝碳化后力学性能及微观结构进行分析,得出喷射混凝土抗压强度、劈裂抗拉强度及抗折强度随着碳化深度增大而增大,且喷射混凝土中原始微气孔及裂缝中钙矾石、氢氧化钙等晶体为CaCO3晶体的成核和生长提供有利条件,碳化产物持续生成并阻塞毛细孔,使其密实度增加,力学性能增大。     

Ultrasonic testing and microscopic analysis on concrete under sulfate attack and cyclic environment

The damage process of concrete exposed to sodium sulfate attack and drying-wetting cycles was investigated. The water to binder（W/B） ratio and the concentration of sulfate solution were taken as variable parameters. Through the experiment, visual change, relative dynamic modulus of elasticity（RDME） and the surface damage layer thickness of concrete were measured.Furthermore, SEM and thermal analysis were used to investigate the changing of microstructure and corrosion products of concrete.The test results show that the ultrasonic velocity is related to the damage layer of concrete. It approves that an increase in damage layer thickness reduces the compactness and the ultrasonic velocity. The deterioration degree of concrete could be estimated effectively by measuring the surface damage layer and the RDME of concrete. It is also found that the content of gypsum in concrete is less than that of ettringite in test, and some gypsum is checked only after a certain corrosion extent. When the concrete is with high W/B ratio or exposed to high concentration of sulfate solution, the content of ettringite first increases and then decreases with corrosion time. However, the content of gypsum increases at a steady rate. The content of corrosion products does not correspond well with the observations of RDME change, and extensive amount of corrosion products can be formed before obvious damage occurs.     

钢纤维混凝土抗冻性能试验研究

为了研究钢纤维混凝土的抗冻性能,采用快冻法进行了0%、0.5%、1.0%、1.5%、2.0%五种不同钢纤维掺量的混凝土在水中和3.5%氯化钠溶液中冻融试验。通过分析冻融循环次数和钢纤维体积率对钢纤维混凝土冻融后质量损失、劈裂强度损失和相对动弹性模量变化的影响,分析了冻融环境下钢纤维对混凝土的增强机理。并且用压汞法和SEM从微观上研究了钢纤维混凝土的孔径分布特征,讨论了微观结构对其抗冻性能的影响。研究表明,在冻融循环作用下掺入适量的钢纤维能够减小混凝土内部的孔隙率、增加密实度,有效阻止混凝土内部微裂缝的产生与发展,提高混凝土的抗冻性能。钢纤维掺量对混凝土抗冻性影响显著,掺量为1.5%时,钢纤维对混凝土抗冻性能改善效果最好。     

Deterioration mechanism of sulfate attack on concrete under freeze-thaw cycles

The experiments of concrete attacked by sulfate solution under freeze-thaw cycles were investigated. The sulfate solution includes two types of 5% Na2SO4 and 5% MgSO4. Through the experiment, microstructural analyses such as SEM, XRD and TGA measurements were performed on the selected samples after freeze-thaw cycles. The corrosion products of the concrete were distinguished and quantitatively compared by the thermal analysis. Besides, the damage mechanism considering the dynamic modulus of elastically of concrete under the coupling effect was also investigated. The experimental results show that, under the action of freeze-thaw cycles and sulfate attack, the main attack products in concrete are ettringite and gypsum. The corrosion products exposed to MgSO4 solution are more than those to Na2SO4 solution. Furthermore, the content of gypsum in concrete is less than that of ettringite in test, and some of gypsum can be observed only after a certain corrosion extent. It is also shown that MgSO4 solution has a promoting effect to the damage of concrete under freeze-thaw cycles. Whereas for Na：SO4 solution, the damage of concrete has restrained before 300 freeze-thaw cycles, but the sulfate attack accelerates the deterioration process in its further test period.     

锈蚀钢筋混凝土压弯构件非线性有限元分析

通过选用合适的材料本构模型和粘结滑移模型，建立了锈蚀钢筋混凝土构件的有限元分析模型，以钢筋锈蚀率和轴压比为变量，对锈蚀钢筋混凝土压弯构件进行数值分析，旨在为在役锈损结构的非线性分析奠定基础．分析结果表明，钢筋锈蚀率和轴压比同时影响着锈损构件的性能劣化；构件的承载能力和变形能力均随锈蚀率的增加而降低；粘结力退化加剧了构件性能劣化，且小轴压比构件对粘结力退化更为敏感；就锈蚀率而言，构件性能劣化较粘结性能退化有一定的滞后；性能降低幅度也与轴压比有关，小轴压比构件的退化幅度相对较大；对于高轴压比构件，变形能力退化较少，而承载力退化幅度大于变形退化幅度．