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A Basic Study on Microstructure and Chloride Diffusivity of Deteriorated Concrete due to Construction Defects

施工缺陷劣化混凝土微观结构和氯离子扩散率的基础研究

基本信息

批准号：
12650467
负责人：
SAKURADA Ryoji
金额：
$ 2.43万
依托单位：
Akita National College of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-12650467/
关键词：
construction joint chloride-ion rapid chloride permeability test pore volume microcrack 打継ぎ施工不良

项目摘要

This study reveals that the effect of pore structure on chloride-ion migration into the deteriorated concrete due to construction defects. Rapid drying of hardened concrete and construction joints, which may give problems in lowering of water-tightness, are picked up here as factors of construction defaults.For this purpose, the rapid chloride permeability test was employed in the evaluation of chloride-ion penetration into mortar, and the pore size distributions of mortar matrix were analyzed by a probability density function. The main findings from the results can be summarized as follows.(1) The pore size distribution of dried concrete can be statistically explained by Weibull distribution function. The shape parameter depends on drying temperature. The elevation of drying temperature induces a larger volume of capillary pores in the range of 50nm-2μm in diameter, ruling strongly the chloride-ion diffusivity based on the information of the capillary pore volume and the statistical parameters. A simplified prediction model of chloride-ion migration into concretes is established that could have an applicable to a broad range of drying conditions.(2) An increase in pore volume ranging from about 1nm-10μm in diameter of the construction joint is remarkable for the mixture of higher water-cement ratio. The construction joint produces difference of chloride diffusion coefficient between joint zone and non-joint zone at early ages. Although the difference decreases with time, the values of the chloride diffusion coefficient along the joint surfaces are slightly higher than that of non-joint zone even at later ages.(3) The chloride-ion diffusion coefficient of mortar using unhydrated cement, which is recovered from fresh cement paste by freeze-drying, is 20% higher than that of mortar using ordinary portland cement.

研究结果表明，混凝土孔结构对氯离子向混凝土中迁移的影响是由施工缺陷引起的。针对混凝土硬化后快速干燥和施工缝易导致水密性降低的问题，采用快速氯离子渗透试验对氯离子渗透砂浆进行评价，并采用概率密度函数分析砂浆基体的孔径分布。结果的主要发现可归纳如下。(1)干燥后混凝土的孔径分布可用威布尔分布函数进行统计解释。形状参数取决于干燥温度。干燥温度的升高导致了直径在50 nm-2μm范围内的毛细孔体积的增加，根据毛细孔体积和统计参数的信息，强有力地控制了氯离子的扩散系数。建立了适用于各种干燥条件的氯离子向混凝土中迁移的简化预测模型。(2)水灰比越大，施工缝的孔容增加越明显，孔容范围在1 nm ~ 10μm之间。施工缝在早期产生了缝区与非缝区氯离子扩散系数的差异。尽管这种差异随时间的推移而减小，但即使在较晚的龄期，节理面沿着的氯离子扩散系数仍略高于非节理面。(3)采用冷冻干燥法从新鲜水泥浆体中回收未水化水泥的砂浆的氯离子扩散系数比采用普通波特兰水泥的砂浆的氯离子扩散系数高20%。