Study On Freezing-thawing Damage Model Of Polypropylene Fiber Concrete

In northern cold region in China, the main damage of the concrete structure is the freeze-thaw. The reason why the material internal structure degradation is alternating positive and negative temperature difference. As the poor of freezing-thaw resistance, ordinary concrete doesn’t meet the requirements of the durability in the cold. Polypropylene fiber has many characteristics, such as inhibition of micro cracks in concrete, so freeze-thaw resistance of polypropylene fiber concrete is the key point of this study.In general, the material and structure has initial damage. In fact, freeze-thaw lead to the materials destruction of the whole process eventually. And damage mechanics is a discipline to study material micro defects and eventually lead to the occurrence and development process. So the theory of damage mechanics is adopted to study the characteristics of freeze-thaw resistance of polypropylene fiber concrete.The different content of polypropylene fiber is carried on in the test, the fiber content is 0%, 0.75% and 1.5%, the number of freeze-thaw is 25,50, 75,100,125,150,175 and 200 respectively, measuring the quality, the relative dynamic modules of elasticity compressive strength, flexure strength, and the three-point bending flexural strength. According to the different damage phenomenon, the rule of Mechanical properties in the freeze-thaw resistance of polypropylene fiber concrete is concluded. Base on the research actuality of damage mechanics,this article summarize the research of damage mechanics and introduce a variety of representative damage model of concrete.The mechanism of concrete in freeze-thaw and reinforced mechanism of fiber are analysed.By staying the character of freeze-thaw damage,we can found that freeze-thaw damage can be regarded as material fatigue damage and freeze-thaw damage has a certain randomness.Random variables of damage need to meet certain distribution. The damage model that is based on two-parameter Weibull distribution is given.With fitting to experiment data and estimating to the parameter,the damage model of polypropylene fiber concrete in different fiber content is established.Finally,we build the relational expression of damage and compressive strength. The research results in this paper show that the freezing-thawing resistance, 1.5% dosage of fiber in concrete is most powerful, plain concrete is weakest. 0.75% admixture of concrete is the worst of the compressive strength, flexural performance are compared with plain concrete has obvious improvement; 1.5% admixture of concrete flexural strength does not change significantly compared with dosage of 0.75%. Overall analysis of polypropylene fiber added to significantly improve the frost resistance of concrete performance, especially the ability of resistance to freezing and thawing damage.