Experimental Study On The Concrete Crack Fracture And Damage Scale

As a quasi-brittle material,due to the influence factors such as pouring vibration,maintenance environment and properties of material itself,there will have different degrees of damage inside and outside of the concrete before it reaches fracture failure under external force.So it will be of great value for scientific research and practical engineering to understand the fracture mechanism of concrete material and evaluate the working stability of concrete structure by using the reliable method of test to perform some experimental works about the concrete fracture according to the fracture damage characteristics of concrete material.The following content shows the main work of this paper and research conclusion is as follows:(1)According to the three-point bending beam of fracture test,the whole crack propagation curves(P-CMOD)was obtained.Combined with the digital image correlation(DIC)method,the whole field displacement and strain information were also obtained,and then investigated the fracture and damage process of concrete specimen.The results indicate that the P-CMOD curves which was obtained from the DIC method and experimental data agrees well.During the whole crack propagation process,the crack mouth opening displacement(CMOD)and crack-tip opening displacement(CTOD)basically show a linear relationship.(2)The double-K parameters which include the initial toughness and unstable toughness was calculated based on the simplified extreme theory,and compared the results with double-K method.Meanwhile,the variation rule of fracture toughness with specimen geometry and maximum coarse aggregate size was also obtained.(3)The experimental calibration method of concrete damage scale was studied and by using the DIC method,the properties of damage scale of concrete with different specimen geometry and maximum coarse aggregate size was also investigated.The results indicate that the concrete damage scale shows an increasing tendency with the experimental load.The permissible damage scale(damage scale at the peak load)shows obviously size effect,it increases with the specimen geometry,and shows an opposite tendency with the increasing maximum coarse aggregate size.(4)The permissible damage scale of every concrete specimen was obtained through the theoretical method,and by comparing the permissible damage scale values which were obtained from the DIC method,the nationality of the experimental calibration method of permissible damage scale was verified.