Title: Fracture of Concrete Subjected to Cyclic and Sustained Loading

Author(s): Surendra P. Shah and Sushil Chandra

Publication: Journal Proceedings

Volume: 67

Issue: 10

Appears on pages(s): 816-827

Keywords: cement pastes; compressive stress;concretes; crack propagation; creep properties;cyclic loads; deformation; failure mechanisms;microcracking; research; strains; ultrasonic tests;volume change.

DOI: 10.14359/7312

Date: 10/1/1970

Abstract:
To study the mechanics of failure of concrete subjected to slowly applied cyclic or sustained stresses, sealed specimens of paste and concrete were tested under the maximum cyclic or sustained compressive stresses of 60 to 90 percent of the ultimate stress. Volumetric strains, ultrasonic velocity and attenuation, and internal microcrack propagation were examined. Sustained or cyclic loading resulted in progressive crack propagation. For stresses lower than 70 percent of the ultimate, when failure did not occur within the test duration, cracks propagated at a relatively slow rate. This crack growth was called Stage I. Stage II crack growth was associated only with failure and was characterized by a faster growth rate of microcracks, a sharp increase in volume dilation, and rapid changes in ultrasonic measurements. Crack growth under sustained stresses appeared to result from the phenomenon of stress corrosion while under cyclic loading the process of load repetition seemed to play an important role. Sustained loading also had a strengthening effect on concrete, probably because of the consolidation of the hardened cement paste.