不同冻融循环次数混凝土单轴压缩试验

为研究冻融循环作用对混凝土力学性能的不利影响，分别对混凝土进行0，10，25，35和50次快速冻融循环，并利用10 MN大型多功能动静力三轴仪对混凝土历经40%f_c的荷载历史作用后(f_c=40 MPa为普通混凝土单轴抗压强度)，以10-4/s的应变速率进行单轴压缩试验，得到冻融循环后混凝土的单轴抗压强度，并分析其损伤演化规律与破坏机理。结果表明:随着冻融循环次数的增加，历经相同加载历史作用后的混凝土的单轴抗压强度逐渐降低，且峰值应力随冻融循环次数的变化呈二次曲线关系；选用修正后的Weibull-Lognormal分段式损伤本构模型，经验证能够较好拟合冻融劣化混凝土历经荷载历史作用后单轴应力应变曲线；此外，冻融循环次数越多，对混凝土造成的损伤程度越大，在损伤发展的后期阶段，冻融程度较大的混凝土损伤路径大幅度延长且趋于扁平化，直至进入破坏阶段。

Experimental studies on dynamic properties of concrete under different freeze-thaw cycles

In order to make studies of unfavorable effects of the freezing and thawing cycles upon the dynamic properties of the concrete, the laboratory tests, which suffered 40% of fc loading history of the concrete specimens after 0, 10, 25, 35 and 50 cycles of the freezing and thawing (fc defined as the uniaxial compressive strength of the ordinary concrete) were carried out by a 10 MN large multi-purpose static and dynamic triaxial apparatus at a strain rate of 104/s. The uniaxial compressive strength of the concrete under the action of the cyclic freezing and thawing was obtained, and the damage evolution law and failure mechanism were analyzed. The testing results show that the uniaxial compressive strength of the concrete decreased with the increase in the number of the freeze-thaw cycles, and the peak stress along with the change of the freeze-thaw cycles was characterized by a quadratic curve relationship. And from the testing results it is found that the validated Weibull-Lognormal segment type damage constitutive model can be well used for fitting the uniaxial stress-strain curves of the concrete deteriorated by the freeze-thaw cycle damages after the loading histories. In addition, the number of the freeze-thaw cycles of the concrete is more, the degree of damage to the concrete is greater, and in the later stages of damage development, the damage path of the concrete with a large degree of freezing and thawing is greatly prolonged and tends to flattening until it is in the damage stage.