【作者】 牛建刚；

【导师】 牛荻涛；

【作者基本信息】 西安建筑科技大学 ， 结构工程， 2008， 博士

【摘要】 处于一般大气环境中的混凝土结构种类繁多,数量巨大。工业化的进程,导致全球大气污染日趋严重,环境中CO₂浓度的加大以及酸雨范围的扩大,使混凝土的中性化问题越来越受关注。混凝土中性化是钢筋锈蚀的前提条件,一般大气环境下混凝土中性化和钢筋锈蚀是混凝土结构耐久性的主要研究内容。此外,混凝土结构总处于承载状态下,结构的应力状态会对混凝土的耐久性产生影响。研究受荷状态下粉煤灰混凝土在酸雨和碳化共同作用时的中性化性能,为进一步研究混凝土中钢筋的锈蚀与混凝土结构的寿命预测奠定了基础,对混凝土结构的耐久性设计及其评估具有重要的意义。论文选取一般大气环境下影响混凝土结构耐久性的力学因素（弯曲荷载）和环境因素（CO₂和酸雨）组合,设计了多因素耐久性试验方案和具体实施方法,通过试验研究了单一、双重和多重影响因素作用下粉煤灰混凝土的中性化性能,揭示了它们的作用机理和性能退化规律,最终建立了一般大气环境粉煤灰混凝土结构中性化深度预测模型。主要研究内容如下:从扩散传质角度分析了气态的CO₂和液态的酸雨与混凝土发生中性化反应的过程,揭示了混凝土碳化和混凝土遭受酸雨侵蚀中性化的机理。在对全国酸雨成分调查和分析的基础上,提出了试验室模拟酸雨溶液的配制方法以及采用浸烘循环制度加速酸雨侵蚀的试验方法。分析了国内外耐久性试验加载装置的优缺点,确定了适合于多因素耐久性试验的加载方式,为开展多因素作用下混凝土中性化试验研究,以及建立粉煤灰混凝土中性化深度预测模型奠定了基础。开展了粉煤灰混凝土快速碳化试验,研究了各种因素（水胶比、粉煤灰掺量、浇筑面）对粉煤灰混凝土碳化规律的影响以及CO₂二维扩散作用对构件角区碳化深度的影响;进行了粉煤灰混凝土酸雨侵蚀模拟试验,采用混凝土表层溶蚀、质量变化、力学性能降低和中性化深度等评价指标研究了粉煤灰混凝土的酸雨侵蚀规律,分析了不同酸雨侵蚀影响因素对评价指标的影响。结果表明,酸雨不仅使混凝土表面出现剥蚀、骨料外露,还使混凝土质量减小、强度降低、中性化深度加大。首次考虑酸雨和CO₂的共同作用,在分析混凝土酸雨侵蚀机理、碳化机理以及二者共同作用特点的基础上,设计了酸雨和碳化共同作用试验模式,通过一般大气环境中酸雨侵蚀和碳化共同作用粉煤灰混凝土的耐久性试验,研究了粉煤灰混凝土在酸雨侵蚀和碳化共同作用下的性能退化规律,分析了二者之间的耦合效应,得出了混凝土酸雨侵蚀和碳化共同作用的机理。考虑应力状态对混凝土耐久性的影响,研究了一般大气环境承载混凝土在不同侵蚀介质作用下的耐久性能,通过承载混凝土试件的快速碳化试验、酸雨侵蚀试验、酸雨和碳化共同作用循环试验,分析了弯曲荷载水平对粉煤灰混凝土侵蚀规律及中性化的影响,提出了混凝土中性化弯曲应力影响系数的计算公式。分析了影响粉煤灰混凝土碳化的主要因素,在粉煤灰混凝土碳化机理的基础上进行了粉煤灰混凝土碳化模型的推导,建立了粉煤灰混凝土的碳化深度预测模型。通过对混凝土水化过程、碳化机理的深入分析,提出了模型参数——完全碳化时单位体积混凝土吸收二氧化碳的量m₀的计算方法,并给出了工程中常用粉煤灰混凝土的简化实用公式;基于气体在混凝土中扩散机理的分析,给出了另一个重要的模型参数——二氧化碳在混凝土中有效扩散系数D_e的计算公式。从传质学理论入手,首次建立了酸雨侵蚀混凝土中性化理论模型,研究了模型中各参数的取值,从材料因素和环境因素两方面确立了酸雨侵蚀粉煤灰混凝土有效扩散系数D_A的计算公式。以混凝土碳化作用为主,首次建立了一般大气环境下考虑酸雨作用和荷载影响的粉煤灰混凝土中性化深度预测模型。通过模型计算值和试验结果的比较验证了中性化深度预测模型,计算值与试验结果吻合较好,该模型为一般大气环境下粉煤灰混凝土结构的寿命预测提供了科学依据。更多还原

【Abstract】 There are a great number of concrete structures existing in the atmospheric environment.The process of industrialization has led to the severe air pollution.The CO₂ concentration increases and acid rain areas expand so that the neutralization of concrete is increasingly concerned about.The neutralization of concrete and the steel corrosion are the main aspects in the durability of concrete structures,and the neutralization of concrete is the prerequisite for steel corrosion.Moreover,the durability of concrete is greatly influenced by the stress state as the actual structures are under external loads.Therefore,the neutralization of fly ash concrete under load subjected to the simultaneous attack of acid rain and carbonation should be investigated,which is significant for the durability design and assessment and for the further investigation of reinforcement corrosion and service life prediction of concrete structures.In this paper,the multi-factor durability program and how to carry out the tests were designed based on the combination of the mechanical（bending load） and environmental factors（CO₂ and acid rain）.Then the effects of single,double and multiple influencing factors on the neutralization of fly ash concrete were investigated, and the action mechanism and the rule of performance degradation were revealed. Finally,a predicting model of neutralization depth of fly ash concrete in the atmospheric environment was proposed.The main contents of this paper are as follows:Firstly,the neutralization process of CO₂ and acid rain was analyzed through the theory of diffusion and mass transfer and the mechanism of carbonation and acid rain attack together was revealed.The method to simulating acid rain solution in laboratory was proposed and the cyclic soaking-drying to accelerate the acid rain attack was introduced on the basis of the survey and analysis on the components of acid rain around China.The advantages and disadvantages of the load devices for durability test were analyzed,and the devices suitable for the multi-factor durability tests were adopted.The above works would be helpful to carry out the neutralization tests and establish the predicting model of neutralization depth for fly ash concrete.Secondly,laboratory accelerated carbonation tests were carried out.The two dimensional diffusion of CO₂ on the carbonation depth of the corner concrete was investigated,and the carbonation rule of fly ash concrete was obtained considering the influencing factors（water-binder ratio,the amount of fly ash,casting surface）.At the same time,the accelerated acid rain tests were carried out in the laboratory.Parameters such as surface condition,mass,cube compressive strength and neutralization depth of concrete were used to evaluate the acid rain resistance of fly ash concrete.Then,the degree of the different influencing factors on the evaluating index was analyzed.The acid rain attack not only made concrete surface desquamate,aggregates denudate,but also made concrete mass decrease,compressive strength reduce and neutralization depth increase.Thirdly,test modes of acid rain and carbonation working together were built up on the basis of the mechanism and the characteristics of acid rain and carbonation separately.Then,durability tests of acid rain and carbonation working together on fly ash concrete were carried out.It is the first time that acid rain and CO₂ in the atmospheric environment as two important corrosive media were considered.The coupling effects were further analyzed and the mechanism of acid rain and carbonation working together was obtained.Fourthly,accelerated carbonation test,acid rain attack test,and simultaneous attack test of acid rain and carbonation of concrete under load were carried out.The neutralization and corrosion mechanism of fly ash concrete under load was investigated in different corrosive media.The calculation formula of the bending stress coefficient of concrete neutralization was suggested.By virtue of the bending stress coefficient of concrete neutralization,the influence of stress levels on concrete neutralization was analyzed.Fifthly,a predicting model of carbonation depth of fly ash concrete was established on the basis of analysis of carbonation mechanism and main influencing factors of fly ash concrete.The calculation of parameter m₀,that is the amount of CO₂ absorbed by unit volume of concrete completely carbonated,was proposed by the analysis of concrete hydration process and carbonation mechanism,and the simplification formula of fly ash concrete applied in practice was suggested.The calculation of another important parameter D_e,that is the effective diffusion coefficient,was also proposed on the basis of the mechanism gas diffusion in concrete.Finally,a neutralization model for fly ash concrete subjected to acid rain attack was proposed for the first time on the basis of the theory of diffusion and mass transfer.The values of the model parameters were studied,and the calculation formula of effective diffusion coefficient DA was established considering both material and environmental aspects.A neutralization predicting model of fly ash concrete in the atmospheric environment emphasizing the role of carbonation was established for the first time on the basis of carbonation model.The effects of acid rain and bending loads were taken into account in this model.The model is reasonable as the results calculated by the model agree well with test results,and it can be used as a reference for the predicting of service life of fly ash concrete structures.更多还原