基于环境的海工混凝土

单一因素作用下砼耐久性标准试验没有基于使用环境,根据试验结果不能对实际环境砼工程使用寿命作出科学预测,也无法量化指导实际工程砼耐久性设计;针对目前海工砼耐久性试验与寿命预测研究中存在的问题,本文在以下几个方面做了探索性和创新性研究工作:1)探讨了不同环境条件下有害物质在混凝土中的传输机制及其与混凝土性能劣化关系的基本理论,为建立与使用环境相适应的混凝土寿命预测模型奠定基础;2)对海工砼耐久性与寿命预测中两个基本问题即砼孔溶液制取方法问题及砼中钢筋锈蚀临界值问题进行了讨论;建立了一种较为简便实用的混凝土人工孔溶液制备方法,初步建立了这种人工孔溶液与压滤孔溶液之间的相关关系;同时对钢筋锈蚀临界值的分析表明,钢筋锈蚀临界值不只受氯离子含量一个参数控制,它同时也是混凝土碱度的函数,理论分析和大量数据表明钢筋腐蚀电位是混凝土中氯离子浓度的对数和混凝土pH值的线性函数;3)针对目前砼氯离子扩散系数快速测试方法研究中存在的问题,对应用电化学快速测试氯离子扩散系数的基本理论、适用条件和修正方法进行了讨论,提出了基于饱海水电阻率的海工砼氯离子扩散系数测试方法;结果表明饱海水电阻率法不仅在理论上满足了稳态条件,而且在实践中与海水自然扩散法得到的结果具有良好的相关性;试验结果还表明在砼中复合掺加粉煤灰和矿渣粉可大幅度降低砼氯离子扩散系数;同时对不同水胶比普通混凝土与大掺量废渣混凝土在饱海水环境混凝土的使用寿命进行了Monte Carlo数值模拟;4)采用适度提高压力梯度的方法测试了长龄期与高性能混凝土气体扩散系数,所测结果较前人基于浓度梯度方法测试结果数量级大致相同;同时基于混凝土毛细吸水动力学特性的研究分析了混凝土孔结构、计算了其连通孔隙率,发现基于计算得到的连通孔隙率与气体有效扩散系数高度相关,而计算混凝土理论总孔隙率与气体扩散系数相关性较差,表明连通孔隙率控制砼气体扩散过程而不是总孔隙率;建立的基于砼连通孔隙率的气体有效扩散系数计算模型为大气环境混凝土工程质量控制和寿命预测提供了便利条件;5)在对混凝土碳化模型深入研究基础上,建立了与钢筋锈蚀临界pH值相联系的修正的碳化理论模型,从而为碳化与氯离子渗透共同作用下钢筋砼寿命预测奠定基础;初步建立了模拟海洋大气盐雾环境下砼在氯离子渗透和碳化共同作用下砼耐久性加速试验方法,并对不同水胶比普通混凝土与掺工业废渣砼损伤失效过程进行了试验研究,根据试验结果建立了基于氯离子和氢氧根浓度二参数的钢筋锈蚀临界状态方程,同时对不同水胶比普通混凝土与大掺量废渣混凝土损伤失效过程及使用寿命预测进行了数值计算和分析;6)建立了考虑毛细管吸入、冻融损伤以及氯离子结合的潮汐环境钢筋砼氯离子扩散模型;初步建立了模拟海洋潮汐环境砼在冻融循环、干湿交替共同作用下砼耐久性加速试验方法,并对不同水胶比普通混凝土与掺工业废渣砼损伤失效过程进行了试验研究,建立了基于氯离子和氢氧根浓度二参数组合的钢筋锈蚀临界状态方程,并且基于试验结果对海洋潮汐环境下不同水胶比普通混凝土与大掺量废渣混凝土使用寿命进行了Monte Carlo数值模拟。本文通过对不同区位环境下海工砼耐久性加速试验方法研究,探索基于区位环境的海工混凝土损伤失效过程及其规律,建立适用于海水浸渍环境、海洋大气环境、海洋潮汐环境的海工砼使用寿命预测模型,基本实现根据砼所处环境、水泥与胶凝材料品种、水胶比、砼构造(保护层厚度)等参数对砼使用寿命进行预测,也可以按照指定使用寿命对适用于不同环境的砼进行设计和控制,为最终实现钢筋砼结构的耐久性设计奠定基础。
逆变焊机

The durability accelerated testing methods based on single-factor action are invalid in service life prediction and durability design of marine concrete in engineering because of absence of multi- factor action of similar actual environment.Airming at these problems of research on durability testing methods and method of service life prediction,some innovative study work are explored in this paper.The main contents and achievements are as follows:1)The transfer mechanisms of harmful substance in concrete and relationship between transfer mechanism and deterioration mechanism of marine concrete in various environmental conditions are discussed.Foundation on service life prediction based on zone environment is established.2)The two basic issues of study on marine concrete durability and service life prediction,which are pore solution making method of concrete and depassivation critical value of steel bar embedded in concrete are investigated.A simple and practical artificial pore solution making method of concrete is presented,and relationship between the parameter such as [OH-] of this artificial pore solution and that of expression pore solution is established.Analyse on the depassivation critical value of steel bar embedded in concrete indicate that the depassivation critical value of steel bar is not only dominated by the parameter of [Cl-],but by the parameter of [OH-] or alkalinity of concrete,and a series of theoretic analyse and experimental data also indicate that half-cell potential of steel bar embedded in concrete is the bivar linear function of log[Cl-] and pH value of pore solution of concrete.3)Based on analysis and summarization of rapid testing methods for chloride diffusion coefficient of concrete, two issues concerned in this field have been put forwarded. Aiming at solving the problems, basic theory, application condition, as well as amendatory methods on rapid testing chloride diffusion coefficient of concrete based on electrochemistry method have been discussed, and a new method for chloride diffusion coefficient of marine concrete saturated with seawater ground on electrical resistivity measurement has been suggested. Experimental results show that this new method is not only correct in theory but dependable in practice. At the same time the experimental results also indicated that the chloride diffusion coefficient can be decresed greatly by adding 25% FA and 25% SG replacing 50% cement in concrete.Service life prediction on normal concrete and concrete with high conctent FA and SG of various W/B is completed by using Monte Carlo stochastic simulation method.4) On the basis of study of gas transfers mechanism into porous medium materials, a calculation formula of gas effective diffusion coefficient of concrete based on pressure grads and water saturation has been deduced according to the relevant theory. According to the testing method and calculation formula,the gas effective diffusion coefficient of HPC and old concrete with higher pressure grads has been tested and calculated. Making use of the relationship model between the gas effective diffusion coefficient of concrete and the gas diffusion coefficient in straight capillary pore, the pore tortuosity factor in concrete has been caculated. The experimental results is basically coincide with that of Switzerland scholar Houst F I and Wittmann Y F using concentration grads method. The analysis of pore structure indicates that the total pore ratio of concrete calculating from cement paste pore ratio by using MIP thchnique can bring prodigious