Dear Dr. Waldemar Łasica ,

I suggest you to have a look at the following reports/papers:

-AN INVESTIGATION INTO THE USE OF FIBRES IN CONCRETE INDUSTRIAL GROUND-FLOOR SLABS

By Wafa Labib and Nick Eden

Available at: https://www.irbnet.de/daten/iconda/CIB9056.pdf

-Effect of Synthetic Fibers on Structural Behavior of Concrete Slabs-on-Ground

Jeffery R. Roesler, Salah A. Altoubat, David A. Lange, Klaus-Alexander Rieder, and Gregory R. Ulreich

Aci Materials Journal 103(1):3 (2006)

Available on RG at: https://www.researchgate.net/publication/249968013_Effect_of_synthetic_fibers_on_structural_behavior_of_concrete_slabs_on_ground

-Design methods for fibre-reinforced concrete: a state-of-the-art review

Anette Jansson, Kent Gylltoft, Ingemar Löfgren

Project: Fiber reinforced concrete

Available on RG at: https://www.researchgate.net/publication/228778780_Design_methods_for_fibre-reinforced_concrete_a_state-of-the-art_review

-Mechanical properties of steel and polymer fiber reinforced concrete

Reza Babaie, Milad Abolfazli and Ahmad Fahimifar

Journal of the Mechanical Behavior of Materials, Volume 28: Issue 1 (2019)

Available at: https://www.degruyter.com/view/journals/jmbm/28/1/article-p119.xml?language=en

-Amazing Types, Properties, and Applications of Fibres in Construction Materials

Abbas Mohajerani, Siu-Qun Hui, Mehdi Mirzababaei, Arul Arulrajah, Suksun Horpibulsuk, Aeslina Abdul Kadir, Md Tareq Rahman, and Farshid Maghool

Materials (Basel), 12(16): 2513 (2019)

Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6721013/

-ITAtech Guidance For Precast FIbre Reinforced Concrete Segments - Vol. 1 : Design Aspects

By ITAtech Activity Group Support – Report n.7 (2016)

Available at: https://www.google.it/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwj-u8SLy5rrAhUHzKQKHfzDCEEQFjAFegQIBxAB&url=https%3A%2F%2Fabout.ita-aites.org%2Fwg-committees%2Fitatech%2Fpublications%2Fdownload%2F1495_1ae2aacb16ee523cb37fabac09609fc6&usg=AOvVaw2vFvx_CPR4KOkEsuCUFaSN

Best regards, Pierluigi Traverso.

Thank you Pierluigi Traverso for detailed references.

There are numerous factors (variables, both from polymer and matrix) responsible which affect shrinkage stress in the concrete or other composite materials.

Article Design methods for fibre-reinforced concrete: a state-of-the...

The best percentage or quantity of the polymer can be determined by using different proportions of the polymer.

Then, by making different measurements, the best ratio is known, which can be used for different purposes.

That is, the only way to find out the optimal ratio is by continuous experimentation