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Mechanism of Developing Cold Joint in Concrete, Its Pore Structure and Repair Technique

混凝土冷缝产生机理、孔结构及修复技术

基本信息

批准号：
13650619
负责人：
TANAKA Kyoji
金额：
$ 2.11万
依托单位：
Tokyo Institute 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：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13650619/
关键词：
Concrete Mortar Placing Joint Cold joint Permeability Environmental Condition Pore structure Repair 水密性打ち足し時間

项目摘要

A time gap in placing between two concrete layers and environmental condition at concrete placing is found out to be the main cause for producing a cold joint in a concrete member. It is because that the first concrete layer started hydration at long interval time before placing of the second concrete layer and at higher temperature. To discuss quantitatively effect of the two parameters, liquid permeability of mortar specimens that were produced at several placing intervals and at various temperatures were measured. The equation for calculating permeability composed of interval time and temperature was proposed on the basis of the experimental results.As for the effect of outdoor environment on permeability, specimens with cold joints were made at several interval times of placing in summer and winter and the difference in influence of the seasons on formation of a cold joint was discussed. Furthermore permeability of each specimen was estimated by calculation using temperatures of the specimens. The usefulness of the above method to estimate to permeability of a cold joint is also confirmed in an actual field.A new technique, in which gallium is intruded m pores of a specimen at high pressure and then the distribution of it is mapped by an EPMA measurement, was developed for studying the structure of a cold joint. It was made clear that a discontinuous plane was formed along the cold joint in concrete and it became more noticeable at longer interval time and at higher temperature.To make a cold joint watertight three kinds of repair agents, mainly composed of magnesium silicofluoride and calcium silicate, were injected in cold joints at low pressure, and their permeability were measured. It was found out that they produced some crystals in cold joints and decreased their permeability. It was also confirmed by the observation of pore structures at the cold joints that the structures became dense.

混凝土两层间浇筑的时间差和混凝土浇筑时的环境条件是混凝土构件产生冷缝的主要原因。这是因为第一层混凝土在浇筑第二层混凝土之前的较长时间间隔内开始水化，且温度较高。为了定量地讨论这两个参数的影响，对不同放置间隔和不同温度下的砂浆试件进行了液体渗透率的测试。在试验结果的基础上，提出了由时间间隔和温度组成的渗透率计算公式。对于室外环境对渗透率的影响，在夏季和冬季的几个放置间隔时间制作了冷缝试件，并讨论了季节对冷缝形成的影响的差异。此外，通过计算试件的温度来估计每个试件的渗透率。提出了一种新的研究冷缝结构的方法，即在高压下将镓注入试件的孔洞中，然后用电子探针测量其分布。为了使混凝土冷缝不透水，在低压下向冷缝内注入了以氟化硅镁和硅酸钙为主的3种修补剂，并对其渗透性进行了测试。研究发现，它们在冷缝中产生了一些晶体，降低了其透气性。冷连接处气孔结构的观察也证实了组织变得致密。