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类型 基础研究 预答辩日期 2018-03-10
开始(开题)日期 2015-12-23 论文结束日期 2017-12-25
地点 九龙湖土木新大楼214会议室 论文选题来源 973、863项目     论文字数 10 (万字)
题目 FRP筋增强混凝土结构耐久性能及其设计方法研究
主题词 玄武岩纤维增强复合材料(BFRP),加速老化,退化机理,长期性能预测,海水海砂混凝土(SWSSC)
摘要 纤维增强复合材料(FRP)的耐腐蚀性能是其相比于普通钢材的一大突出优势,FRP筋被视为在极端腐蚀性环境下替代易锈蚀钢筋的理想材料。但由于FRP筋,尤其是玄武岩纤维增强复合材料(BFRP)筋的开发应用年限较短,对其在实际服役环境下的性能退化规律和退化机理的了解并不充分,导致FRP筋长期性能的不确定性反成为困扰FRP筋应用的关键问题之一。因此,开展针对FRP筋增强混凝土结构耐久性能的研究具有重要的现实意义。此外,得益于FRP筋优秀的耐氯离子侵蚀性能,FRP筋与海水海砂混凝土的组合应用正在吸引广泛的研究兴趣,但目前相关的耐久性研究还比较少。本文采用加速老化试验、微-细观观测和理论计算分析相结合的方法,对FRP筋增强混凝土结构长期耐久性能中涉及的关键问题进行了研究,具体的研究内容及成果包括: (1) 首先,对两种树脂基体的BFRP筋(环氧树脂和乙烯基酯树脂)在60℃碱溶液浸泡环境下的性能退化规律和退化机理开展了加速试验研究。结果显示,BE筋(玄武岩纤维-环氧树脂)的耐碱性能优于BV筋(玄武岩纤维-乙烯基酯树脂),纤维/树脂的界面脱粘是BFRP筋力学性能退化的主要原因;然后,对BE筋在两种碱性环境(碱溶液浸泡和潮湿混凝土包裹)下的退化规律进行了对比试验研究。结果显示,BE筋在碱溶液浸泡环境下的退化速率是潮湿混凝土包裹环境下的2.67倍;最后,对BE筋在应力和腐蚀性溶液(酸、碱、盐和水)共同作用下的耐久性能开展了加速试验研究,并结合Arrhenius公式,对BE筋的长期性能进行了预测研究。结果显示,碱溶液环境对BE筋的侵蚀速率要高于其他溶液环境(酸、盐和水),当应力水平低于20%的极限抗拉强度时,应力对退化速率的加速效果不明显,长期性能预测结果表明,在北纬30°、40°和50°三地区各自的年平均温度下,浸泡在碱溶液中的BE筋,其抗拉强度保留率达到50%所需时间分别为4.2年、7.4年和16.1年。 (2) 首先,研究比较了纤维种类、树脂基体种类以及表面处理方式等对FRP筋与普通混凝土在海洋环境下的粘结耐久性的影响。结果显示,BFRP筋和玻璃纤维增强复合材料(GFRP)筋的粘结耐久性能基本相当,碳纤维增强复合材料(CFRP)筋的粘结耐久性能最优,乙烯基酯树脂基体的FRP筋的粘结耐久性能要差于环氧树脂基体,表面喷砂处理可以提升粘结耐久性能;然后,进一步对新型钢-连续纤维复合筋(SFCB)与河沙/海砂混凝土在海洋环境下的粘结耐久性进行了比较研究。结果显示,海砂中的盐分可能对SFCB在混凝土碱性环境中的耐久性有一定的正面影响,可以降低微孔隙溶液的碱性,延缓SFCB表面BFRP的退化速度;最后,对BFRP筋和SFCB与天然海水海砂混凝土在不同拉拔试件形式下(中心拉拔和偏心拉拔)的粘结耐久性能开展了加速试验。结果显示,同等条件下,中心拉拔组的极限粘结强度都要高于偏心拉拔组,整体而言,海水浸泡环境下的粘结性能退化要比干湿循环环境下的严重。 (3) 对FRP筋增强混凝土梁在模拟海洋环境下的抗弯性能演化开展了多批次的试验室加速试验,分析比较了环境作用时间、受拉筋材种类、混凝土种类(普通混凝土/海水海砂混凝土)、箍筋类型(FRP箍/钢筋箍)以及加速环境类型(干湿循环/浸泡)等参数的影响。试验结果表明,经过最长1年的荷载和海水干湿循环共同作用后,批次I(普通混凝土梁)中的GFRP筋、BFRP筋和SFCB梁的抗弯承载力保留率分别为72%、58%和62%,SFCB梁的屈服荷载保留率为75%。经过最长3个月的荷载和海水干湿循环共同作用后,批次II(海砂混凝土梁)中的普通钢筋和SFCB梁的特征荷载都没有特别显著的变化,荷载-挠度曲线的斜率都得到了提高,钢筋梁和SFCB梁的能量延性指标也都得到了提高,并且后者的提高幅度更为明显。最后,在批次III中(海水海砂混凝土梁),对采用全复合材料配筋(箍筋和架立筋也是BFRP筋)的天然海水海砂混凝土梁,在经历加速海洋环境作用后的抗弯性能变化进行了系统研究。结果显示,BFRP筋梁和CFRP筋梁的破坏模式都由受压区混凝土压溃破坏逐步向剪-压破坏模式转变,SFCB梁的破坏模式由受压区混凝土压溃破坏逐步向SFCB拉断破坏转变,经过最长9个月的环境作用后,BFRP筋梁、CFRP筋梁和SFCB梁的极限承载力保留率分别为79%、70%和89%。 (4) 基于现有的FRP筋长期性能预测方法,进一步考虑混凝土包裹层、实际服役环境温度波动的影响,提出了更精细化的长期性能预测模型。基于所提出的预测模型,结合文献中已有的BFRP筋加速老化试验数据,对预测模型的应用进行了示例展示,求解给出了BFRP筋环境影响折减系数的建议值。另外,对实际服役环境温度和湿度条件下BFRP筋的极限粘结强度退化规律进行了预测,结合本文和文献中BFRP筋与混凝土短期粘结试验数据,拟合得出了短期极限粘结强度的计算公式,在得出的公式中引入预测得出的极限粘结强度损伤因子,给出了考虑极限粘结强度退化的BFRP筋基本锚固长度计算方法。 (5) 对FRP筋增强混凝土梁在正常使用极限状态下的抗弯刚度和最大裂缝宽度的计算公式进行了系统的校核和修正。基于本文试验数据并参考已有文献中的试验数据,在理论分析和计算的基础上,提出了修正的FRP筋增强混凝土梁短期抗弯刚度计算公式。针对FRP筋粘结性能变化对截面抗弯刚度计算的影响进行了概念分析。借助近年来国内外开展的有关FRP筋增强混凝土受弯构件裂缝宽度的实测数据,对最大裂缝宽度计算公式中的各系数的取值进行了系统校核,提出了修正的FRP筋增强混凝土梁最大裂缝宽度计算公式。
英文题目 Study on the Durability of FRP bars Reinforced Concrete Stuctures and Its Design Method
英文主题词 basalt fiber reinforced polymer (BFRP); accelerated aging; degradation mechanisam; long-term performance prediction; seawater sea sand concrete (SWSSC)
英文摘要 The corrosion resistance of fiber reinforced polymer (FRP) composites is one of their outstanding advantages over ordinary steel, FRP bars are considered as an ideal alternative to steel bars which are prone to corrosion in extremely corrosive environments. However, FRP bars, especially the basalt fiber reinforced polymer (BFRP) bars, have a short development and application time. The understanding of their degradation law and degradation mechanism under actual service environment is not enough. As a result, the uncertainty of their long-term performance becomes one of the key problems that plague their wide application. Therefore, it is of great practical significance to carry out researches on the durability of FRP bars reinforced concrete structures. In addition, because FRP bars have excellent resistance to chloride ions attack, the combination of FRP bars and seawater and sea sand concrete (SWSSC) is attracting a great deal of research interest. However, the related durability studies are still very limited. In this paper, accelerated aging test, micro-meso-observation and theoretical calculation and analysis are combined to study the key issues involved in the long-term durability of FRP bars reinforced concrete structures. The main research work and conclusions are listed as follows. (1) Firstly, accelerated aging tests were conducted to investigate the degradation law and to reveal the inherent degradation mechanism of the BE (Basalt/Epoxy) bar and the BV (Basalt/Vinyl ester) bar by immersing them in 60℃ alkaline solution. The results showed that the durability of BE bars was better than that of BV bars. The fiber/resin debonding was the main reason for the degradation of the mechanical properties of BFRP bars. Then, a comparative study on the degradation of BE bars in two types of alkaline environments (i.e. alkaline solution immersion and moist concrete wrapping) was carried out. The results showed that the degradation rate of BE bars immersed in alkaline solution was 2.67 times higher than that embedded in moist concrete. Finally, the durability of the BE bar under the combined effect of stress and corrosive solution (i.e. acid, alkali, salt and water) was investigated, and the long-term performance of the BE bar was predicted based on Arrhenius theory. The results showed that the durability of BFRP bars exposed to acid, salt and de-ionized water were less affected than that of bars exposed to alkaline solution. The effects of sustained stress on the degradation of BFRP bars were not obvious when the stress level was less than 20% of the ultimate strength. The predicted times required for a tensile strength reduction of 50% for BE bars immersed in alkaline solution at an area with a northern latitude of 30°, 40° and 50°, were 4.2 years, 7.4 years and 16.1 years, respectively. (2) Firstly, the effects of fiber types, resin matrix types and surface treatment methods on the bond durability of FRP bars embedded in normal concrete in marine environment were studied. The results showed that the bond durability of BFRP bars and glass fiber reinforced polymer (GFRP) bars were basically the same, and the bond durability of carbon fiber reinforced polymer (CFRP) bars was the best. The bond durability of FRP bars with epoxy matrix was better than that of FRP bars with vinyl ester matrix. Sand-coating the FRP bar improved the long-term bond durability. Then, the bond durability of the new steel-FRP composite bar (SFCB) embedded in river sand or sea sand concrete in marine environment was further studied. The results showed that the salt ions contained in the sea sand concrete, which can reduce the alkalinity of the microporous solution in concrete, may had some positive effect on the bond durability of the SFCB by reducing the degradation rate of the surface BFRP layer of the SFCB. Finally, accelerated aging tests were performed on the bond durability of BFRP bars and SFCBs with SWSSC under two types of pull-out tests scheme (i.e. direct pull out and eccentric pull out). The results showed that under the same conditions, the ultimate bond strengths in direct pull out condition were all higher than those in eccentric pull out conditon. Overall, the bond degradation in seawater immersion environment was worse than that in the wet-dry cycling environment. (3) Several batches of accelerated aging tests were conducted on the long-term flexural performance of FRP bars reinforced concrete (RC) beams in simulated ocean environment. The influences of aging times, types of tensile reinforcements, types of concrete (i.e. normal concrete or seawater and sea sand concrete), types of stirrups (i.e. FRP bar or steel bar) and types of accelerated environment (i.e. wet-dry cycling or immersion) were analyzed and compared. Experimental results showed that the retentions of flexural capacity of GFRP bars, BFRP bars and SFCB RC beams in batch I (normal concrete) were 72%, 58% and 62%, respectively, after conditioned in sustained load and sea water wet-dry cycling coupled environment for a maximum of 1 year, and the retention of the yield load of SFCB reinforced beam was 75%. After conditioned in load and sea water coupled environment for a maximum of 3 months, there were no significant changes in the characteristic loads of ordinary steel bars and SFCB reinforced sea sand concrete beams in batch II (sea sand concrete). Both the flexural stiffness and energy ductility of all the conditioned beams increased, and these improvements were more significant for the SFCB beams. Finally, in batch III (SWSSC), a systematic study was conducted on the changes of flexural behavior of SWSSC beams reinforced with all-composite reinforcements (i.e. longitudinal reinforcement, stirrups and hanger bars are all FRP bars) under accelerated ocean environment. The results showed that the failure modes of BFRP bars RC beams and CFRP bars RC beams gradually changed from concrete crushed to shear-compression coupled failure, and the failure mode of SFCB RC beam gradually changed from concrete crushed to the SFCB ruptured. The retentions of flexural capacity of BFRP bars RC beams, CFRP bars RC beams and SFCB RC beams in batch III were 79%, 70% and 89%, respectively, after a maximum of 9 months’ environmental condition. (4) By referring to the existing prediction methods, a more refined long-term performance prediction model for FRP bars was proposed with the influence of concrete-wrap and seasonal temperature fluctuations further considered. Based on the proposed prediction model and the existing accelerated aging data of BFRP bars available in the literature, the detailed steps for the application of the model was illustrated, and a recommended environmental reduction factor for the new BFRP bar was given. In addition, the degradation law of the ultimate bond strength of BFRP bars under actual service temperature and humidity was predicted. Based on the short-term bond test data of BFRP bars in this paper and in the literature, a calculation formula for the short-term ultimate bond strength was obtained by fitting method. Then, by introducing the damage factors obtained from the degradation law of the ultimate bond strength to the formula, calculation methods for the basic anchorage length of the BFRP bar located at different environments were given. (5) The calculation formulas of the flexural stiffness and the maximum crack width of FRP bars reinforced concrete beams under service load were systematically checked and modified. Based on the experimental data in this paper and the experimental data in the existing literature, a modified formula for calculating the short-term flexural stiffness of FRP bars reinforced concrete beams was proposed according to theoretical analysis and calculation. A conceptual analysis of the effect of changes of bond properties of FRP bars on the calculation of the flexural stiffness was carried out. Based on the measured data of crack widths of FRP bars RC flexural members at home and abroad in recent years, the values of the coefficients implied in the calculation formula of the maximum crack width were systematically checked, and a modified formula for the calculating of the maximum crack width of FRP bars RC beams was proposed.
学术讨论
主办单位时间地点报告人报告主题
东南大学 2017-4-27 逸夫建筑馆7楼 董志强 FRP增强超高性能砼模壳板的制备工艺及专利研发
东南大学 2017-4-18 逸夫建筑馆15楼 Aftab Mufti Static and fatigue behavior of steel-free bridge deck
东南大学 2016-11-13 逸夫建筑馆15楼 Bijan Khaleghi Accelerated bridge construction use of innovative design, materials and construction methods
东南大学 2015-10-26 逸夫建筑馆15楼 左剑 Higher education for sustainable development
东南大学 2017-03-07 逸夫建筑馆15楼 董志强 海洋暴露试验平台建设项目论证汇报
根特大学 2014-12-15 Magnel Lab 董志强 Research presentation
莫纳什大学 2017-11-17 Melbourne 董志强 Durability of sea water sea sand concrete (SWSSC) beam reinforced with new steel-FRP composite bars in ocean environment
东南大学 2016-03-03 榴园新华厅 钱七虎 提升隧道建设信息化水平,促进安全高效上台阶
     
学术会议
会议名称时间地点本人报告本人报告题目
FRPRCS-12 & APFIS-2015 2015-12-14 南京 Experimental analysis of deformations and tension-stiffening in concrete beams reinforced with BFRP bar and SFCB
第八届全国建设工程FRP应用学术交流会 2013-8-5 哈尔滨 加速老化环境下纤维增强复合材料筋耐腐蚀性能试验研究
     
代表作
论文名称
A refined prediction method for the long-term performance of BFRP bars serviced in field environment
Experimental study on the bond durability between steel-FRP composite bars (SFCBs) and sea sand conc
Bond and Flexural Behavior of Sea Sand Concrete Members Reinforced with Hybrid Steel-Composite Bars
 
答辩委员会组成信息
姓名职称导师类别工作单位是否主席备注
薛伟辰 正高 教授 博导 同济大学
艾军 正高 教授 硕导 南京航空航天大学
潘金龙 正高 教授 博导 东南大学
魏洋 正高 教授 博导 南京林业大学
汪昕 正高 教授 博导 东南大学
      
答辩秘书信息
姓名职称工作单位备注
李慧乐 其他 讲师 东南大学