The Study On Anti-crack Function And Damage Of Concrete By Unixial Tension

Aiming at the cracking-resistance property of concrete in uniaxial tension, this paper analyzed the cracking resistance of concrete at uncontinuous points by means of discontinuous point method, ultrasonic method and proportion limits method , The research subjects were plain concrete, concrete adding fly ash, concrete adding superplasticizer, and steel fiber concrete. According to the uncontinuous points measured by ultrasonic wave method, it was concluded that under the same high stress, the amplitude variation of cracking resistance of steel fiber concrete was greatest , while that of concrete adding fly ash and that of concrete adding superplasticizer were close.The main difference among the three was the relative stress increasing at discontinuous points of the three appeared different while the ultimate tension strength increased, in which the increasing of the concrete adding superplasticizer was the lowest. The discontinuous points and the stress of the discontinuous points got from proportion limits method indicated the same conclusion.Cracking is a common question, and is one of main causes that affect the durability of concrete structure. Due to the complicated reasons of crack producing, it is difficult to analyze and calculate the relation. In this paper, the analytic method afforded by damage mechanics was used, and percentage which cracks occupied to the volume was used as a damage variable,the uncontinuous points were analyzed and compared, at last differences of the cracking resistance of concrete in different states were studied. The results showed that: as to concrete adding fly ash and steel fiber concrete, not only damage variable of discontinuous points were increased; but also the tension strain was improved, delayed the appearance of first crack, so cracking resistance of concrete was decreased ,too; while as to concrete adding superplasticizer, the tension strain of first discontinuous point was decreased, so cracking resistance of concrete was decreased as well.The experimental results indicated that: the cracking-resistance property of concrete adding fly ash and superplasticizer and steel fiber concrete was increased preferably, while that of concrete adding superplasticizer was improved weakly in the relative degree of the three.