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Control of cracking caused by autogenous shrinkage in mass concrete

大体积混凝土自收缩裂缝的控制

基本信息

批准号：
07650531
负责人：
MIYAZAWA Shingo
金额：
$ 1.34万
依托单位：
ASHIKAGA 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：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-07650531/
关键词：
Concrete High- strength concrete Mass concrete Autogenous shrinkage Crack Thermal stress 収縮

项目摘要

Influences of cement type, mix proportion, temperature and specimen size on autogenous shrinkage of concrete were investigated. Influence of autogenous shrinkage on cracking of mass concrete was also investigated with restraining tests where temperature and stress histories of specimens were controlled. Main results of this research are as follows.(1) Influence of cement type on autogenous shrinkage can be setimated with mineral compositon and degree of hydration. Autogenous shrinkage increases by using blast furnace slag with 6000-8000 cm^2/g Blaine Fineness.(2) Predicting model for autogenous shrinkage strain of concrete was proposed. It is function of cement and admixture type, water-binder ratio and effective age. The proposed model is effective for concretes with ordinary Portland cement and with water-binder ratio between 0.2 and 0.56.(3) The rate of autogenous shrinkage increases with temperature of concrete within the range from 20 to 60 ﾟC.It is proved that this effect can be estimated with maturity concept. Autogenous shrinkage during the first 24 hours is lager for a specimen with lager dimensions.(4) Contribution of autogenous shrinkage to restrained stress is increased with decrease in water-cement ratio. For silica fume concrete with water-cement ratio of 0.20, tensile stress generates even when temperature is still increasing. This is because autogenous shrinkage overcomes expansion due to temperature rise.

研究了水泥种类、配合比、温度和试件尺寸对混凝土自收缩的影响。通过控制试件温度和应力历史的约束试验，研究了自收缩对大体积混凝土开裂的影响。本研究的主要结果如下。(1)水泥种类对自收缩的影响可以通过矿物组成和水化程度来确定。使用Blaine细度为6000-8000 cm ^2/g的高炉渣，自收缩增大。(2)提出了混凝土自收缩应变的预测模型。它是水泥和外加剂类型、水胶比和有效龄期的函数。该模型适用于普通波特兰水泥和水胶比在0.2和0.56之间的混凝土。(3)在20 ~ 60 ° C范围内，混凝土的自收缩率随温度的升高而增大，证明这种影响可以用成熟度概念来估计。对于较大尺寸的试样，在最初24小时内的自收缩较大。(4)自收缩对约束应力的贡献随水灰比的减小而增大。对于水灰比为0.20的硅灰混凝土，即使温度仍在升高，也会产生拉应力。这是因为自生收缩克服了由于温度升高而产生的膨胀。