Research of the process of formation of main cracks in samples of concrete during mechanical tests

More strict safety requirements for buildings and structures of critical infrastructures imply that the physical and mechanical properties of construction materials should be correctly assessed and criteria should be established for their durability limit conditions under which main cracks may appear. The paper describes mechanical tests of cores from cement elements obtained from different depths, determining the average values of uniaxial compressive strength, tensile strength, and deformation moduli. The internal structure of C28/35 concrete specimens (disks 5—10 mm thick) was examined with a UDL 2M automated laser ultrasonic flaw detector; longitudinal wave velocities were measured, the values of which ranged from 3820 m/s to 4330 m/s. Cracks no more than 3 mm long were detected in the specimens. The remaining specimens were subjected to uniaxial compression and their acoustic emission was simultaneously measured. A sharp increase in the activity of acoustic emission was observed when the stress reached 0.7Rc and 0.7Rp, where Rc and Rp are the ultimate uniaxial compressive and tensile strengths, respectively. Subsequent examination of the specimens with X-ray showed that main cracks appear at 0.7Rc and 0.7Rp. It is shown that cohesion decreases from 7.5 MPa to 5 MPa and the angle of internal friction decreases by 3 % if stress-state simulation using the Coulomb-Mohr model takes into account the limit state of concrete durability and replaces Rc and Rp by 0.7Rc and 0.7Rp, respectively.

 

Keywords: concrete samples, axial compression strength, laser ultrasound, longitudinal wave velocities, acoustic emission, activity, x-ray tomography.
For citation:

Borisov N. G., Belov O. D., Gapeev A. A. Research of the process of formation of main cracks in samples of concrete during mechanical tests. MIAB. Mining Inf. Anal. Bull. 2021;(4-1):52— 61. [In Russ]. DOI: 10.25018/0236_1493_2021_41_0_52.

Acknowledgements:
Issue number: 4
Year: 2021
Page number: 52-61
ISBN: 0236-1493
UDK: 620.179.17+539.421
DOI: 10.25018/0236_1493_2021_41_0_52
Article receipt date: 20.01.2021
Date of review receipt: 23.02.2021
Date of the editorial board′s decision on the article′s publishing: 10.03.2021
About authors:

Borisov N. G.1, PhD-student, bng@sste.ru;
Belov O. D.1, engineer;
Gapeev A. A.1, engineer;
1 National University Science of Technology MISIS, Mining Institute, Moscow, Russia.

 

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