早期受冻损伤混凝土应力-应变试验研究

Experimental Study on Stress-Strain of Concrete Damaged by Early Freezing

北方地区混凝土冬季施工过程,新浇筑混凝土容易因突然降温而遭受早期损伤。为研究早期受冻对混凝土单轴受压状态下力学性能的影响,通过对不同冻结温度(-5℃、-10℃)、不同起冻时刻(1.0 h、3.5 h、8.0 h、24.0 h)养护条件下的混凝土进行单轴受压试验,获得了应力-应变全曲线,拟合得到了适用于早期受冻混凝土的单轴受压本构方程。结果表明:早期受冻后混凝土应力-应变曲线在下降段更为陡峭,延性和塑性变形能力降低;冻结温度对峰值应力和峰值应变影响不明显;随起冻时刻的延后,峰值应力先下降后上升,峰值应变先上升后下降,初凝后至终凝前受冻混凝土力学性能损伤最为严重;基于过镇海教授模型拟合得到的早期受冻后混凝土应力-应变曲线方程与试验曲线吻合较好;对早期受冻混凝土峰值应力、峰值应变及延性和塑性变形能力最不利的起冻时刻均在养护4 h前后。

During the winter construction of concrete in northern areas,the newly poured concrete often suffers damage due to sudden temperature drop.In order to study the effect of early freezing on the mechanical properties of concrete under uniaxial compression,the uniaxial compression tests of concrete under the curing conditions of different freezing temperatures(-5℃,-10℃)and different freezing moments(1.0 h,3.5 h,8.0 h,24.0 h)were carried out,the full stress-strain curve under uniaxial compression was obtained,and the constitutive equation suitable for uniaxial compression of early frozen concrete was obtained by fitting.The results show that the change trend of the stress-strain curve of concrete after early freezing is basically similar to that of normal cured concrete,but in the descending section,the early frozen concrete is steeper,and the ductility and plastic deformation ability are reduced.The freezing temperature has no obvious effect on the peak stress and peak strain.With the delay of the freezing time,the peak stress first drops and then rises,and the peak strain first rises and then drops.The mechanical properties of frozen concrete after the initial setting and before the final setting are the most severely damaged.The stress-strain curve equation of early frozen concrete based on the fitting of Professor Guo Zhenhai’s model is in good agreement with the experimental curve.The most unfavorable freezing point for the peak stress,peak strain,ductility and plastic deformation ability of the early frozen concrete is around 4 h after curing.