Effect of the sample size on the mechanical and acoustic characteristics of concrete

One of the important features of the fracture of heterogeneous materials with a stress concentrator is the scale effect associated with the dependence of the nominal stress on the specimen size. This effect must be considered when studying the fracture process of concrete to improve the operation safety of concrete structures. The purpose of this work is to study the size effect of the specimens with a notch made of a concrete (class B25, R = 28 MPa) on the strength characteristics and parameters of the acoustic emission(AE) recorded in the process of fracture. Three-point bend tests with registration of AE signals were carried out using specimens of three sizes (1075, 465, and 215 mm long), their geometry corresponded to two-dimensional similarity, since the thickness of the specimens remained unchanged, and both length to width ratio for the specimen and notch remained constant. The size of the zone of fracture localization at different stages of crack development were estimated on the larger specimens using planar AE location and the time dependence of the zone size was plotted. The size of the localization zone of small specimens was determined by measuring the ultrasound attenuation coefficient. Analysis of the loading diagrams combined with the time dependences of the AE parameters revealed that the specimen size affects the fracture staging. The dependences of the rated strength, fracture energy, b_AE-parameter, and the total number of AE signals on the specimen size are plotted. It is shown that the size effect is associated with a decrease in the rated stress for the large-sized specimens and number of accumulated acoustic emission signals, as well as with an increase in the fracture energy and b_AE-parameter. It is assumed that change in the AE characteristics with increasing size of the specimen is attributed to a decrease in the relative fraction of structural heterogeneity (the ratio of the average size of granite aggregate to the specimen size) in large specimens. New data were obtained regarding the effect of the size of concrete specimens on the acoustic characteristics.

1. Walsh P. F. Crack initiation in plain concrete / Magazine of Concrete Research. 1976. Vol. 28. N 94. P. 37 – 41.

2. Bažant Z. P. Size effect in blunt fracture: concrete, rock, metal / Journal of Engineering Mechanics. 1984. Vol. 110. N 4. P. 518 – 535.

3. Bažant Z. P. Scaling of quasibrittle fracture: asymptotic analysis / International Journal of Fracture. 1997. Vol. 83. N 1. P. 19.

4. Bažant Z. P., Ožbolt J., Eligehausen R. Fracture size effect: review of evidence for concrete structures / Journal of structural engineering. 1994. Vol. 120. N 8. P. 2377 – 2398.

5. Hu X., Wittmann F. Size effect on toughness induced by crack close to free surface / Engineering fracture mechanics. 2000. Vol. 65. N 2 – 3. P. 209 – 221.

6. Carpinteri A., Chiaia B., Ferro G. Size effects on nominal tensile strength of concrete structures: multifractality of material ligaments and dimensional transition from order to disorder / Materials and Structures. 1995. Vol. 28. N 6. P. 311.

7. Carpinteri A., Chiaia B. Power scaling laws and dimensional transitions in solid mechanics / Chaos, Solitons & Fractals. 1996. Vol. 7. N 9. P. 1343 – 1364.

8. Shiotani T. Application of the AE Improved b-Value to Quantiative Evaluation of Fracture Process in Concrete-Materials / Journal of acoustic emission. 2001. Vol. 19. P. 118 – 133.

9. Shiotani T., Bisschop J., Van Mier J. G. M. Temporal and spatial development of drying shrinkage cracking in cement-based materials / Engineering Fracture Mechanics. 2003. Vol. 70. N12. P. 1509 – 1525.

10. Carpinteri A., Lacidogna G., Niccolini G. Damage analysis of reinforced concrete buildings by the acoustic emission technique / Structural Control and Health Monitoring. 2011. Vol. 18. N 6. P. 660 – 673.

11. Carpinteri A., Grazzini A., Lacidogna G., and Manuello A. Durability evaluation of reinforced masonry by fatigue tests and acoustic emission technique / Structural Control and Health Monitoring. 2014. Vol. 21. N 6. P. 950 – 961.

12. Brigante M., Sumbatyan M. A. Acoustic methods for the nondestructive testing of concrete: A review of foreign publications in the experimental field / Russian Journal of Nondestructive Testing. 2013. Vol. 49. N 2. P. 100 – 111.

13. Kirane K., Bažant Z. P. Size effect in Paris law and fatigue lifetimes for quasibrittle materials: Modified theory, experiments and micro-modeling / International Journal of Fatigue. 2016. Vol. 83. P. 209 – 220.

14. Botvina L. R., Petersen T. B., Tiutin M. R. Assessment and Analysis of b-Parameter of Acoustic Emission / Zavod. Lab. Diagn. Mater. 2011. Vol. 77. N 3. P. 43 – 50 [in Russian].

15. Ermolov I. N., Lange Iu. V. Non-Destructive Testing: A Handbook in 7 Volumes. Volume 3. Ultrasonic testing. — Moscow: Mashinostroenie. 2004. — 864 p. [in Russian].

16. Bažant Z. P. Scaling laws in mechanics of failure / Journal of Engineering Mechanics. 1993. Vol. 119. N 9. P. 1828 – 1844.

17. RILEM TC.FMC 1. Determination of the fracture energy of mortar and concrete by means of three-point bend tests on notched beams / RILEM Recommendations for the Testing and Use of Constructions Materials. — E & FN SPON, 1994. P. 99 – 101.

18. Hoover C. G., Bažant Z. P. Comprehensive concrete fracture tests: size effects of types 1 & 2, crack length effect and postpeak / Engineering Fracture Mechanics. 2013. Vol. 110. P. 281 – 289.

19. Nimbolkar P. V., Shete M. Effect of aggregate size on fracture parameters of high strength concrete / 14th International Conference on Fracture (ICF 14) June 18 – 23, 2017, Rhodes, Greece.

20. Xu J., Fu Z., Han Q., Lacidogna G., and Carpinteri A. Micro-cracking monitoring and fracture evaluation for crumb rubber concrete based on acoustic emission techniques / Structural Health Monitoring. 2018. Vol. 17. N 4. P. 946 – 958.

21. Botvina L. R., Petersen T. B., Tyutin M. R. The Acoustic Gap as a Diagnostic Sign of Prefailure / Dokl. RAN. Ser. Fiz. 2018. Vol. 63. N 4. P. 174 – 177 [in Russian].

22. Kachanov V. K., Sokolov I. V., Avramenko S. L. The problems of acoustic inspection of large-size concrete building structures / Defektoskopiya. 2008. N 12. P. 12 – 22 [in Russian].

23. Brigante M., Sumbatyan M. A. Acoustic methods in nondestructive testing of concrete: Review of foreign publications in the field of theoretical studies / Russian Journal of Nondestructive Testing. 2013. Vol. 49. N 4. P. 185 – 195.

24. Avramenko S. L. A correlation method for determining the propagation velocity of an acoustic wave in large-size compact concrete articles / Russian Journal of Nondestructive Testing. 2009. Vol. 45. N 1. P. 40 – 49.