【作者】 周立霞；

【导师】 王起才；

【作者基本信息】 兰州交通大学 ， 桥梁与隧道工程， 2011， 博士

【摘要】 西北戈壁地区具有大风、干燥、大温差的气候特点,既有高速铁路高性能混凝土的经验,不能完全适用于戈壁环境。随着西北地区高速铁路大规模建设的开展,研究戈壁环境下高性能混凝土耐久性的实现途径,成为高性能混凝土在戈壁地区得以推广应用迫切需要解决的问题。本文解决戈壁地区高性能混凝土的耐久性问题主要采用“三优化”方法：优化掺合料、优化集料、优化养护技术。首先,矿物掺合料的使用是高性能混凝土实现耐久性所必须的,本文采用Aim和Goff堆积密实模型及扫描电镜,分析了矿物掺合料在水泥基胶凝材料颗粒体系中的作用效应。并且,基于灰色系统理论,分析了矿物掺合料粒度分布、颗粒细度与其胶砂性能之间的相关性,建立了相应的灰色系统模型。本文基于灰系统理论对混凝土所用矿物掺合料进行优化配伍选择,分析了孔结构对混凝土性能的影响规律,并建立了混凝土强度与孔径分布之间的灰系统模型。基于回归方法,建立了孔结构主要参数与混凝土后期强度之间的多元线性数学模型。结果表明：对强度及耐久性要求较低的混凝土可采用单掺粉煤灰；对强度及耐久性要求较高的混凝土可采用粉煤灰和硅灰双掺,考虑经济性则可以采用粉煤灰和矿粉双掺；对强度及耐久性要求高的混凝土可采用粉煤灰、矿粉和硅灰的三掺方式进行配制。其次,现行相关规范对人工集料的使用没有提出明确的指导意见,特别是对碎卵石使用过程中必须要考虑的破碎面问题,说明太过笼统。本文系统研究了碎卵石混凝土的宏观性能,并建立了混凝土强度及耐久性与碎卵石破碎面比例之间的数学关系式。研究表明：高水胶比混凝土可将破碎面控制在40%～60%左右,低水胶比混凝土必须将破碎面控制到60%～80%左右。另外,采用计算机仿真技术建立了卵石粒径与碎卵石破碎面比例之间的模型。结果表明：粒径20mm以下的卵石不可用于破碎碎卵石,粒径30～80mm卵石经一定破碎次数后可获得40～60%左右的破碎面,而粒径在90mm以上的卵石破碎后即可获得70%以上的破碎面。再次,本文采用MIDAS有限元分析软件对桥墩混凝土的温度场进行了模拟,以寻求适宜于戈壁环境的混凝土养护技术。分析表明：采用保温保湿膜养护的桥墩混凝土可以降低混凝土内外最高温差,使表面及中心应力低于允许抗拉强度,避免了温度裂缝的产生。对这一理论研究又采用室内试验进行了验证。为了研究环境对混凝土孔结构的影响规律,本文模拟了大风、干燥、大温差的戈壁环境,采用压汞法测试了混凝土的孔结构分布。结果表明：大风、干燥、大温差对混凝土内部孔隙分布影响显著,会大量增加大的有害孔含量,提高孔隙率,显著增大平均孔径和最可几孔径；若采用保温保湿膜养护,就可显著降低以上危害的程度。本文以兰新二线(新疆段)为依托工程,在具有典型戈壁环境的沿线标段,现场浇筑实体混凝土桥墩。进行了现场实体桥墩的温度场测试及混凝土宏观性能测试。最终,采用实体试验充分说明了戈壁环境下采用保温保湿养护技术的有效性。更多还原

【Abstract】 The Gobi area in northwestern China is characterized by a climate of strong wind, great drought and acute temperature change. So far, the techniques concerning high-performance concrete for high-speed railways built elsewhere have not been well adapted to this area. With the rapid development of high-speed railway construction in this area, the durability research of high-performance concrete for this area is urgently needed. This dissertation deals with the durability problem in three aspects, that is, optimizing the application of admixtures, improving aggregates and enhancing curing techniques, which are detailed as follows, respectively.1. Mineral admixtures are much essential to achieve specified durability for high-performance concrete. Based on Aim-Goff packing model, the effect of mineral admixtures on cement-based composite cementitious systems is analyzed by using scanning electron microscopy (SEM). Based on grey theory, this dissertation discusses the effect of particle size distribution (PSD) and particle fineness of mineral admixture on macro properties of the mortars and establishes a corresponding grey incidence model. The optimal combination of mineral admixtures is studied by using grey analysis and the effect of pore structure on macro properties of the concrete is evaluated, with a grey model for the correlation between pore size distribution and concrete strength presented. A multivariate linear model for the relationship between pore structure parameters and the late strength of the concrete is developed by using regression methods.It is shown that for concrete with low requirements of both strength and durability, a single admixture of fly ash can be adopted; for concrete with high requirements of both strength and durability, a double combination of fly ash and silica fume (alternatively, mineral powder, for economic consideration) can be utilized; for concrete with very high requirements of both strength and durability, a triple combination of fly ash, silica fume and mineral powder can be implemented.2. The current material-related codes and specifications are short of clear instructions on the use of artificial aggregates, especially on the prescription of fracture surface, which shall be considered for crushed cobble. This dissertation includes a systematical study on the macro properties of crushed-cobble concrete, establishing a mathematical relationship of concrete strength and durability versus fracture surface ratio of crushed cobble, and introducing a computer model for particle size versus fracture surface ratio of crushed cobble.The analysis indicates that for the concrete with a large water-cement ratio, the fracture surface ratio should be limited to 40-60%, while for the concrete with a small one it can be 60-80%, so as to achieve necessary strength and durability; generally, cobbles of less than 20mm in size should not be used to make aggregate for concrete; for cobbles of 30-80mm in size, the fracture surface ratio can reach 40-60% after several times of crushing; for cobbles of greater than 90mm in size, the fracture surface ratio would be more than 70% once they are crushed.3. To investigate proper techniques to cure concrete in Gobi’s inhospitable environment, a numerical simulation for the temperature field of concrete in piers of a bridge is performed by using MIDAS, a FEM (finite element method) based software. The analysis shows that the membrane curing can reduce the temperature difference between the inner part and the surface of the pier, make the surface and center stresses lower than the allowable tensile stress, and avoid the occurrence of temperature cracking. Corresponding laboratory tests are also performed to verify the theoretical analysis. With the Gobi environment simulated, the pore structure and distribution are tested by using mercury injection method. The results suggest that the harsh environmental factors, including strong wind, great aridity and acute temperature change as mentioned above, have a significant influence on the pore distribution in the concrete, resulting in the dramatic increase of harmful pore content, porosity, average pore size and the most probable pore size; a membrane curing based on heat and wet preservation can substantially decrease the unfavorable influences.With solid concrete piers constructed on site in the typical Gobi environment of Xinjiang section of the Second Lanzhou-Xinjiang Railway Line, the concrete temperature field is real-monitored and the concrete macro properties are measured to further verify the validity of the membrane curing technique based on heat and wet preservation in Gobi environment.更多还原