Created concrete material by following a 2.79 tutorial in 2.8 and messed up true displacement Here's the tutorial I followed:

https://youtu.be/wmtAVNDtc_w

The only change I made was i skipped a portion with the image texture around 5:30 because i didn't find any major change without it and he youtuber didn't provide any link for the image. So now I'm left with a mesh that ignores true displacement in eevee and takes it too far in cycles

here are some screens links as the page isnt allowing me to upload them directly:
https://photos.app.goo.gl/FPrTejKkSQqiCWVdA

And here is the blender file:
Due to adding vector displacement not so long ago to Blender you have to use dedicated displacement node to convert scalar to vector displacement.



I would say that your shader structure is outdated. It is better to mix RGBs instead of shaders, and use Principled BSDF instead of mixing Diffuse and Glossy. Take a look at the blend file. Although this is not the best example to demonstrate the superiority of the approach, I changed it so it would reflect the idea without altering the artistic component. The shader became heavier but more realistic and PBR.