Urgent, why does steel fiber reinforced concrete crack? Thank you.

Steel fiber will not cause cracking. You should know that concrete is a brittle material with poor tensile strength. The reason for cracking is that the tensile limit of concrete has been reached. Adding steel slag will greatly improve the tensile capacity of concrete. If you don't know, you can check the specific reasons. How does steel fiber aggravate the development of microcracks? It will make people laugh. The causes of cracks are: early autogenous shrinkage of concrete, dry shrinkage of concrete, temperature difference between inside and outside of concrete and load. From what you said, there should be the influence of temperature difference, and then did you let the construction load be used too early before the strength was reached?