These pieces of broken concrete are 3D scans from actual rubble. There are no materials that kind of match what broken concrete looks like. Just the real photographed material on the actual scanned shapes, making them ideal to add to your photo-realistic ruins or for adding that little bit of extra filler for an outdoor environment.
About the models
This set includes three variants of five different chunks of concrete rubble. Raw scans, a high poly set, and a low poly sets. The low poly variants are all quad topology, while the high poly and raw scans are triangulated. The low and high poly sets utilize a 2K PBR texture set per object, while the raw scans are 4K. The largest and most dense model ranges from 1.7M vertexes in raw form, 35K as high poly, down to 518 in it's low poly version.
A little more detail.
The files you will be downloading are OBJ files, as well as a .blend file including all diffuse, normal, and roughness maps.