【作者】 查进；

【导师】 周明凯； 李北星；

【作者基本信息】 武汉理工大学 ， 材料学， 2008， 博士

【摘要】 论文针对超大跨径混合梁斜拉桥预应力宽箱梁易产生开裂这一突出问题,开展宽箱梁高性能混凝土组成设计、裂缝防治、耐久性和温控防裂施工技术研究。通过研究矿物掺合料、聚丙烯纤维、减缩剂和水化热降低剂对混凝土工作性、力学性能、抗裂性能、耐久性能的影响及其作用机理,模拟计算宽箱梁混凝土在不同施工工况条件下的温度场及温度应力场分布情况,为超大跨径混合梁斜拉桥提供了抗裂、耐久的宽箱梁高性能混凝土配合比及有利于箱梁温控防裂的施工技术方案。首先,对宽箱梁混凝土的组成设计进行了研究,从混凝土工作性、力学性能、抗裂性和耐久性为一体的设计要求出发,制备了胶凝材料用量低(490kg·m^-3)、矿物掺合料掺量高（20%～25%）的宽箱梁高性能混凝土,并研究了聚丙烯纤维、减缩剂、水化热降低剂等抗裂组分对该高性能混凝土工作性与力学性能的影响。其后,利用温度-应力试验机、大板法,并辅以水化热、绝热温升、干缩率和徐变度的测试,研究了箱梁混凝土的开裂敏感性和体积稳定性,提出了以温度-应力试验为主的预应力宽箱梁混凝土抗裂性能的评价体系。研究结果表明,箱梁混凝土中掺入矿物掺合料,降低了混凝土绝热温升、干缩率、徐变度和开裂敏感性,有利于混凝土抗裂性能的提高;进一步掺入聚丙烯纤维、减缩剂、水化热降低剂等抗裂组分,发现聚丙烯纤维降低混凝土干缩率和徐变,减缩剂降低干缩率,水化热降低剂降低水化热,进一步有利于混凝土抗裂性能的提高;测试宽箱梁混凝土的各项耐久性指标发现,矿物掺合料的掺入,混凝土抗冻性能和抗氯离子渗透性能提高,碱含量降低,抗碳化性能虽略有下降,但基于混凝土抗碳化性能的耐久性寿命预测超过500年。利用化学结合水、XRD、SEM、MIP等测试方法,对浆体的微观结构与组成进行研究,探讨了粉煤灰对混凝土徐变、干缩、耐久性的作用机理,以及水化热降低剂降热作用机理。研究结果显示:粉煤灰混凝土的徐变性能受到体系水化产物数量、微集料效应和粉煤灰界面结合情况三大因素的共同作用,界面结合力越强,微集料效应发挥程度越高,以及体系的化学结合水量越小,则混凝土徐变度减小越明显。水化热降低剂由于其本身结构中含有的羟基,容易吸附于水泥表面并包裹在未水化的水泥周围,以减少水的进入,减缓水泥水化速度,延长水化时间,从而降低水泥水化热最高值。最后,模拟计算不同施工方案条件下宽箱梁混凝土温度场和温度应力场,分析了浇筑温度、整幅浇筑或分幅浇筑、布置冷却水管或不布置冷却水管等因素对混凝土抗裂安全系数的影响,提出了分幅浇筑且布置冷却水管的防裂技术方案以及控制混凝土内部最高温度和内外温差的防裂措施。更多还原

【Abstract】 Four aspects of high performance concrete for wide box girder were investigated to solve the problem of crack in wide box girder of super-long span hybrid girder cable-stayed bridge, including the mix designing, crack prevention, durability and construction for temperature control and crack prevention. The effect of mineral admixtures, polypropylene fiber, shrinkage reducing agent and hydration heat reducing agent on the workability, mechanical properties, crack resistance and durability and their mechanisms were studied, and the simulation calculations of the temperature fields and stress fields for the prestressed concrete wide box girder were also carried out. Based on all above the results, the proportions of high performance concrete with good crack resistance and good durability were supplied, and the construction for temperature control and crack prevention was also supplied.Firstly, the composition of high performance concrete for wide box girder was investigated. The high performance concrete was prepared to meet the requirement of workability, mechanical properties, crack resistance and durability. What’s more, the influence of polypropylene fiber, shrinkage reducing agent and hydration heat reducing agent on the workability and mechanical properties of high performance concrete were investigated.Secondly, the cracking sensitivity and volumetric stability of HPC for box girder were investigated by means of board device, temperature-stress test machine (TSTM), and testing hydration heat, adiabatic temperature rise, drying shrinkage ratio and creep. And the indexes to assess the cracking sensitivity of concrete for wide box girder were established based mainly on the TSTM. The results indicated that adding mineral admixtures decreased the adiabatic temperature rise, drying shrinkage ratio and creep, which improved the crack resistance of concrete. What’s more, the research results demonstrated that the concrete exhibited less drying shrinkage and creep with polypropylene fiber, less drying shrinkage with shrinkage reducing agent, and less hydration heat with hydration heat reducing agent. The adding of polypropylene fiber, shrinkage reducing agent and hydration heat reducing agent was beneficial to improve crack resistance. The durability test results indicated adding mineral admixtures improved the frost resistance and chloride penetration resistance, but decreased the carbonation resistance. The predicated service life of HPC for boxer girder was more than five hundred years based on the carbonation resistance.The XRD, SEM and MIP methods were applied to determine the microstructure and composition of the cement-based materials with mineral admixtures, and the mechanisms were preliminarily analyzed, including the fly ash improving durability but decreasing drying shrinkage and creep, hydration heat reducing agent reducing hydration heat. The analysis revealed that the creep characteristics of fly ash cement were decided by the amount of hydration products, ’micro-aggregate effect’ and combination of interface around fly ash. The concrete exhibited less specific creep in the stance of less amount of non-evaporable water, ’more micro-aggregate’, and more combination of interface. The analysis also revealed the hydroxyl of hydration heat reducing agent was absorbent around the unhydrated cement particle, which prevent the cement particle touching from the water. So the process of hydration was delayed, and the peek value of hydration heat was decreased.Finally, the simulation calculations of the temperature fields and stress fields for the prestressed concrete wide box girder were carried out under different construction plans. Some factors which affected the coefficient of safety for crack prevention of concrete were investigated, including different casting temperatures, choices of whole amplitude construction or half amplitude construction, and arranges of cooling pipes or not. According to the simulation calculation results, the half amplitude construction with arrangement of cooling pipes was choose to prevent the crack. And some measures to control the maximum temperature and the difference between the inside and outside temperature in boxer girder were put out.更多还原