冻融损伤混凝土力学性能衰减规律

Degradation Law of Mechanical Properties of Concrete Subjected to Freeze-Thaw Cycles

为研究冻融作用对混凝土力学性能的影响,采用快冻法将混凝土盐冻或水冻至不同损伤程度后,测其动弹性模量、抗折强度、抗压强度和劈裂抗拉强度.以动弹性模量为损伤变量,分析了冻融损伤与抗折、抗压强度之间的关系,采用回归分析的方法建立了抗折强度衰减方程.结果表明,混凝土抗压、抗折、劈裂抗拉强度以及动弹性模量均随冻融循环作用次数的增加而逐步降低;抗折、劈裂抗拉强度以及动弹性模量的衰减速率随冻融循环作用次数的增加而不断增大,但抗压强度的衰减速率则是先增大后减小;在冻融循环次数相同的情况下,含气量越高、水灰比越低,混凝土的强度损失越小,其力学性能损失的大小顺序依次为:抗折强度和劈裂抗拉强度、动弹性模量、抗压强度;冻融损伤与抗折强度的相关性较好,但与抗压强度的相关性较差,当冻融损伤小于40%时,混凝土的抗压强度一般不低于其初始强度的70%.

In order to study the influence of freeze-thaw damage on the mechanical properties of concrete, rapid frost experiments were conducted on specimens with varied water to cement ratio and air content, then the tests of the flexural, compressive, tensile splitting strength and dynamical elastic modulus of frozen concrete were carried out. The dynamical elastic modulus was chosen as damage variables, the relationship between freeze-thaw damage and flexural or compressive strength were analyzed, and an attenuation equation on flexural strength of damaged concrete was proposed through regression analysis. The experimental results show that flexural, compressive, tensile splitting strength and dynamical elastic modulus decrease with the increasing freeze-thaw cycles; and the decay rate of flexural, tensile splitting strength and dynamical elastic modulus increases. On the other hand, the decay rate of compressive strength increases at first with the increasing of freeze-thaw cycles, and then decreases. For the same freeze-thaw cycles, the higher is air content or the lower is the ratio of water to cement, the less is strength loss. The descending order of loss of mechanical properties was as follows：flexural and tensile splitting strength, dynamical elastic modulus, compressive strength. The damage degree and the flexural strength were well correlated while its correlation to the compressive strength was weak. When damage degree is less than 40%, the compressive strength of freeze-thaw damaged concrete is not lower than 70% of its original strength.