Yes, there are alternative methods to evaluate fracture toughness of concrete without using a COD (crack opening displacement) measuring device. Some of these methods include:

Flexural strength test: The fracture toughness can be indirectly determined from the flexural strength of concrete beams by using empirical relationships.

Energy methods: The fracture toughness can be estimated from the area under the load-displacement curve obtained from a fracture test using energy methods, such as the Linear Elastic Fracture Mechanics (LEFM) or the Elastic-Plastic Fracture Mechanics (EPFM) methods.

Micro-mechanical testing: Fracture toughness can be evaluated using micro-mechanical tests, such as the indentation technique or the pull-out test, which can provide information on the energy required to initiate and propagate cracks in concrete.

It's important to note that these alternative methods have limitations and their results may not be as accurate as those obtained from COD measurements

Dear Luboš Bocian,

There are many methods to determine the fracture toughness of various types of concrete in Fracture mechanics science, especially in the field of energy criteria. There is a research paper that I recommend to you and I hope it will be useful for you.

Article Review on different testing methods and factors affecting fr...

fracture toughness can be correlated with the compressive strength, tensile strength, and flexural strength of concrete. These relationships are typically established through empirical models based on experimental data.

Two approaches come to mind: the size effect model and the effective crack model. the SEM developed by Bazant was written into the RILEM recommendation, and the size effect of strength tested by geometrically similar specimens can be related to the fracture energy and the length of the fracture process zone. The ECM approach is to calculate the equivalent elastic crack length from the secant compliance of the load- displacement curve and then further calculate the fracture toughness. Both models are classical equivalent linear elastic fracture models, and you can refer to Bazant and Karihaloo's paper for details.

Many Approaches; Size effect law, Bondry effect model, Equivalent approach from Shah method. I recommended reading these papers:

• DOI:
• 10.1016/j.engfracmech.2021.108098
• DOI:
• 10.1007/s43452-022-00424-6
• DOI:
• 10.3221/IGF-ESIS.60.06