How can I acheive this look...

that its moss, do you have a piece of concrete that looks like that

This video is the closest I could find on your question. You need a mold to pour your concrete in. Toward the top of the mold only pour concrete on the sides (instead of solid).

https://www.youtube.com/watch?v=-0bPeURO88A

It appears that the concrete has tiny pebbles added to it which weakens the strength of the concrete with any formal reinforcement. They probably just carefully busted out the areas they wanted exposed with a tool maybe like an ice pick or flat head screwdriver to break only the areas they wanted exposed.

I work in the construction industry,and just from the appearance, that's what bad concrete would be like on a job.

Let styrofoam be your sculptor. Find a tube that has the inner circumference for your sculpture. Now use a smaller cylinder for the carved out part. Carve into the smaller cylinder for the ragged sides and gaps. Be sure the leave the bottom 1/3 solid. If you can’t carve the smaller details you want, do these enhancements later with paint and glue. Cover the cylinder with Saran-type wrap to make removal later much easier. Place the smaller cylinder inside the larger tube. Hold the cylinder to stabilize it. Pour mixed instant cement in the space around the cylinder. Let the cement cure completely, 2-3 days. It will be dry to the touch before then, but curing allows all the elements to form it’s own integrity so the cement won’t crumble. Cut away the foam from the outside, and slide the inner cylinder out. Then add any enhancements you wish, gluing pebbles, scraping and gouging details, or rubbing in paint or oil to creat “leaks” or other pretend defects. Best wishes for your cement vessel. ☺️

Thank you all for some great ideas I'm excited about getting started